Employment 3. Topographical Anatomy of Neck Region. Denudation and Ligation of External and Common Carotid Arteries. Topographical Anatomy of Neck Organs (Larynx, Trachea, Pharynx, Esophagus, Thyroid Gland). Tracheostomy. Operations on Thyroid Gland.
Neck in General The numerous vessels, nerves and visceral structures found in the neck make this region both interesting and important to the surgeon. The upper limits of the neck are the lower border of the jaw, a line extending from the angle of the jaw to the mastoid process, and the superior curved line of the occipital bone. The lower limits are the sternal notch, the clavicles and a transverse line from the acromioclavicular joint to the spinous process of the 7th cervical vertebra. The contour of the neck varies with age and sex, being well rounded in women and children but more angular in men; hence, the landmarks are more conspicuous in the male. In extension, the anterior part of the neck is lengthened, and in flexion it is shortened, so that the distance between its movable parts from the sternum to the lower jaw varies as does the relationship of these parts to the vertebrae. Therefore, it is necessary in giving relative positions of landmarks to suppose that the neck is midway between flexion and extension, this being the natural upright position unless otherwise stated. The anterior portion of the neck contains the respiratory tube (larynx and trachea) and the alimentary tube (pharynx and esophagus); the great vessels and nerves are located on the sides, and the posterior portion contains the cervical segment of the spine and surrounding musculature. The infrahyoid region extends from the hyoid bone above to the suprasternal notch below and is limited laterally by the anterior border of the sternocleidomastoid muscles.
EMBRYOLOGY VISCERAL ARCHES The branchial (visceral) arches are best developed in the human embryo about the last half of the 3rd week of intra-uterine life, at which time they appear as parallel bars. Six such arches are present, and they occupy a region which later becomes the neck. They represent the gill apparatus mechanism of water breathing vertebrates in which the respiratory function is performed by means of a rich vascular tissue that lines the clefts. Water passes through these fringes, permitting the exchange of the oxygen of the water and the carbon dioxide of the blood. In higher vertebrates with the acquisition of aerial respiration, a loss of function in these gill arches takes place, and the number is reduced from 7 as seen in fish to
First, or Mandibular, Arch. This is supplied by the mandibular branch of the 5th nerve and the external maxillary artery. Its muscle mass develops into the muscles of mastication, which are supplied chiefly by the mandibular nerve. This arch becomes differentiated into a shorter upper maxillary process and a longer lower mandibular one,both of which play a large part in the formation of the face. The cartilage of the first arch, referred to as Meckel’s cartilage, is almost entirely replaced by the mandible, but its end persists and forms two of the ear bones, the malleus and the incus.
Second, or Hyoid, Arch. This is suppliedby the facial nerve, and its artery is the external carotid. Its muscle mass becomes the muscles of facial expression and the platysma.The cartilage of the 2nd arch is known as the cartilage of Reichert. From it are developed the Stapes, the Styloid process, the Stylohyoid ligament and the Smaller cornu of the hyoid bone; hence, it can be called the “S” arch. Third, or Thyrohyoid, Arch. This is supplied by the glossopharyngeal nerve and the internal carotid artery. The muscle mass of this arch becomes the stylopharyngeus muscle, and the cartilage develops into the body and the greater cornu of the hyoid bone.Fourth, Fifth and Sixth Arches. These arches are unnamed and somewhat indefinite. However, the 4th arch gives rise to the cricothyroid muscle which is supplied by the external branch of the superior laryngeal nerve. The muscle mass of the 5th arch forms some of the intrinsic muscles of the larynx which are supplied by the recurrent laryngeal nerve. The cartilages of the 4th and the 5th arches become the framework of the larynx. The thyroid cartilage originates from arches 4 and 5; the cricoid, the arytenoids, the rings of the trachea and the bronchi are formed from the 6th arch. The arches enclose the primitive pharynx within which develop the important “T” structures: Tongue, Tonsils, Tube (eustachian), Thyroid, Thymus and paraThyroids. CERVICAL SINUS The 2nd visceral arch, growing faster than the arches below it, soon overhangs them and forms a deep groove known as the cervical sinus. The downgrowing 2nd arch eventually meets and fuses with the 5th, resulting in a space lined by squamous epithelium which normally disappears. However, if this space persists, a branchial cyst results. If the 2nd arch fails to meet the 5th, an opening called a branchial fistula is found along the anterior border of the sternocleidomastoid muscle which is most commonly placed above the sternoclavicular joint. The cleft membrane always forms a septum between such a cyst or fistula and the pharynx. Since a branchial fistula is situated below the 2nd arch and above the 3rd, its course can be readily understood, passing between the internal and the external carotid
FIG. Arrangement and structure of the visceral arches in the fetus. Each arch has a nerve, an artery, a plate of cartilage and a muscle mass. The structures to which each of these gives rise have beeamed in the drawing.
FIG. Formation of a branchial cyst and a branchial fistula in the embryo.
arteries. The facial and the hypoglossal nerves lie superficial to the fistulous tract, and the glossopharyngeal nerve lies deep to it. If the fistula extends upward to the pharyngeal recess it will pass between the stylohyoid and the stylopharyngeus muscles.
SURGICAL CONSIDERATIONS
Branchial cysts should be completely excised and, since there is little adherence to the surrounding structures, these procedures are usually quite simple. A transverse incision is made in a skin crease of the neck so that there is minimal scarring, the proper cleavage plane is found, and the cyst is removed.
Branchial Fistulae. Excision of branchial fistulae (lateral cervical fistulae) tends to be more difficult, since there is adherence to surrounding tissues. It is wise to inject such a fistula with methylene blue and determine whether or not the dye appears inside the pharynx; this also marks the fistulous tract. These operations may be long and difficult. Since complete exposure is necessary, a longitudinal incision along the anterior border of the sternocleidomastoid muscle is advised which extends from the external fistulous opening below to the angle of the jaw. The fistulous tract is dissected from below upward, and the great vessels and the surrounding nerves are protected.
FIG. The course of a branchia fistula (diagrammatic).
An assistant’s finger may be inserted through the mouth to press the region of the internal opening of the fistula toward the surgeon. The incision is deepened through the skin,the superficial fascia and the platysma. Then the superficial layer of deep cervical fascia is incised along the anterior border of the sternocleidomastoid which is freed and retracted posteriorly. The fistulous tract is dissected from below upward to the lower border of the posterior belly of the digastric which is retracted upward. The fistula may pass lateral to both carotids or may dip between them. The pharyngeal part of the dissection requires exact anatomic exposure. Some surgeons have suggested a stepladder type of operation, making multiple transverse incisions.
BONY CARTILAGINOUS FRAMEWORK
The bony cartilaginous framework of the neck consists of the hyoid bone, the thyrohyoid membrane, the thyroid cartilage, the cricothyroid membrane, the cricoid cartilage and the trachea.
Hyoid Bone. This has no immediate relation with the skeleton; it lies in the soft part of the neck at the root of the tongue and possesses great mobility. Mosher has noted the importance of the greater cornu and has stated that 16 major structures of the neck (the glossopharyngeal, the recurrent laryngeal and the phrenic nerves excepted) are in close relation to it. The hyoid bone is on
FIG. Excision of a branchial fistula. The incision extends along the anterior border of the sternocleidomastoid muscle from the fistulous opening below, to the angle of the jaw above. The posterior belly of the digastric muscle and the anterior border of the sternocleidomastoid muscle are retracted in opposite directions, giving adequate exposure. In this case the fistula passes between the external and the internal carotid arteries. The tract is dissected from below upward.
FIG. The bony and cartilaginous framework of the neck.
a level with the 3rd cervical vertebra, and its body is approximately on a level with the angles of the jaw. The upper borders of the cornu are excellent guides to the lingualarteries. Therefore, the hyoid bone is of great surgical importance as a landmark. The external laryngeal muscles and several muscles of the tongue and the floor of the mouth attach to it.
Thyrohyoid Membrane. This membrane is situated between the hyoid bone and the thyroid cartilage. It acts as a ligament which suspends the larynx from the hyoid and attaches to the posterior border of the bone and its greater cornu. The interval between the bone and the cartilage varies from 1 to 1 and1/2 inches.
Thyroid Cartilage. This consists of 2 laminae which are separated behind but united in front to form a projection called the laryngeal prominence or Adam’s apple. The anterior borders of the laminae are joined at their lower halves, but the upper halves are separated and form the V-shaped thyroid notch which can be felt through the skin. This is an important landmark, since the common carotid arteries usually bifurcate t this level. An oblique line is usually visibleon the posterior part of the lateral aspect of the lamina, and it is to this line that the sternothyroid muscle inserts and the thyrohyoid muscle takes its origin.
Cricothyroid Membrane. This membrane closes the space separating the cricoid and the thyroid cartilages. It is lozenge shaped, is widest in the midline and tapers toward the side. Through this space the simplest and most rapid tracheotomy may be performed for the immediate relief of suffocation.
Cricoid Cartilage. This cartilage forms a complete ring encircling the larynx, below the thyroid cartilage. Its narrow anterior part, or arch, is easily felt through the skin and lies on a level with the 6th cervical vertebra. The posterior part, or lamina, is much deeper, projects upward and occupies the lower part of the gap between the two laminae of the thyroid. At this level is the junction of the pharynx and the esophagus, the larynx and the trachea, and here also the common carotid is crossed by the omohyoid muscle. It is also a useful guide in controlling serious hemorrhage from either carotid artery, since at this level pressure may be maintained against the tubercle of the 6th cervical vertebra.
STERNOCLEIDOMASTOID MUSCLE The sternocleidomastoid muscle is the most important surgical landmark in the neck. It arises by two heads: the sternal head originates in front of the manubrium sterni by means of a rounded tendon, and the clavicular head takes origin from the upper border and front of the medial third of the clavicle by muscle fibers. The muscle inserts on the outer surface of the mastoid process and the lateral third of the superior nuchal line. Its nerve supply is derived from the spinal part of the spinal accessory and the 2nd and the 3rd cervical nerves. When both muscles contract, the head becomes flexed on the vertebral column, but contraction of one muscle rotates the head to the opposite side and draws it down toward the chest. The sternocleidomastoid separates the anterior from the posterior triangle of the neck, and many structures which are considered as contents of these triangles actually lie under the muscle. These structures are the common and the internal carotid arteries, the internal jugular vein, the vagus nerve, the scalenus anterior muscle and the cervical plexus. The triangular interval existing between the sternal and the clavicular heads is very evident in thin individuals and appears as a slight depression. Beneath the lower end of this depression and just above the sternoclavicular joint lies the common carotid on the left side and the bifurcation of the innominate artery on the right. The carotid sheath is under cover of its lower part and along its anterior border above. Along its posterior border, the nerves of the cervical and the brachial plexuses are found. The spinal part of the spinal accessory nerve extends backward and downward through its deep fibers.
DEEP CERVICAL FASCIA (FASCIA COLLI)
The important deep cervical fascia consists of 3 layers: superficial (general investing or enveloping fascia), middle (pretracheal fascia) and deep (prevertebral fascia).
SUPERFICIAL LAYER (GENERAL INVESTING OR ENVELOPING FASCIA) The superficial layer of deep cervical fascia is characterized by its tendency to divide, hence its synonyms: investing or enveloping layer. This fascia splits to envelop two muscles (trapezius and sternocleidomastoid), two salivary glands (submaxillary and parotid) and two spaces (space of Burns and a space above the clavicle in the posterior triangle). It extends from the ligamentum nuchae posteriorly to the midline anteriorly where it becomes continuous with its fellow of the opposite side. As it leaves the ligamentum nuchae, it splits to envelop the trapezius muscle, reuniting at the muscle’s anterior border to form the roof of the posterior triangle.
FIG.The deep cervical fascia in cross section. The first or superficial investing layer has been colored red; the second or pretracheal layer is yellow; the third or prevertebral layer is blue.
It divides again at the posterior border of the sternocleidomastoid muscle, the two layers joining at its anterior border to form the roof of the anterior triangle. This layer of fascia is attached above to the external occipital protuberance, the superior nuchal line, the mastoid process (base), the zygomatic arch and the lower border of the mandible. Below it is attached to the acromion process and spine of the scapula, the clavicle and the manubrium sterni. Its enveloping of the submaxillary gland is accomplished by a splitting of the fascia at the lower border of the gland, the superficial layer attaching to the lower border of the mandible and the deep layer to the mylohyoid line. The submaxillary lymph glands are inside of this sheath and in immediate contact with the submaxillary salivary gland; therefore, in the removal of the lymph glands for tuberculosis or carcinoma, the salivary gland also should be sacrificed. The parotid investment is brought about by a splitting which takes place at the lower border of the parotid gland, the deeper layer passing deep to the gland and attaching to the base of the skull. The superficial layer passes superficial to the gland and attaches to the zygomatic arch; this layer is
Fig. The deep cervical fascia in longitudinal section. The same color identification of the 3 layers as was used in previous figure is utilized here.
very dense, and any swelling of the underlying parotid gland causes tension and pain (mumps). The superficial fascia splits below to form 2 spaces: the first is over the lower part of the posterior triangle where it is attached to the clavicle; between its layers are found the descending supraclavicular veins and part of the external jugular vein. The second space is over the lower part of the anterior triangle where it splits and attaches to the front and the back of the manubrium sterni, forming the suprasternal space of Burns. This contains the sternal head of the sternocleidomastoid muscle, the communication of the anterior jugular veins (jugular arch), lymph glands and fat.
MIDDLE LAYER (PRETRACHEAL FASCIA)
This layer is part of the general investing fascia and arises from the deep surface of the sternocleidomastoid muscle. It passes in front of the carotid system (internal jugular vein, common carotid artery and vagus nerve) and divides into the prethyroid and the pretracheal layers or laminae.
Prethyroid Layer. This is a thin lamina which passes in front of the thyroid gland and attaches to it along an irregular line at the junction of the middle and the posterior thirds of the superficial surfaces of each lateral lobe. Therefore, it passes in front of the superior thyroid vessels above and the inferior thyroid veins below. Laterally, it is
FIG. The superficial or enveloping layer of deep cervical fascia. The illustration demonstrates the “fascial envelopes” formed for the submaxillary salivary gland and sternocleidomastoid muscle.
separated from the surface of the gland and from the pretracheal fascia proper by an interval filled with loose areolar tissue which has been aptly referred to by Sloan as the posterior thyroid space. This triangular space is limited anteriorly by the prethyroid lamina, posteriorly by the pretracheal layer proper and medially by the thyroid gland. It is necessary to enter this space before attempting to mobilize the lobe and dislodge it medially.
Pretracheal Layer Proper. This layer passes in front of the trachea and extends behind the posterolateral border of the thyroid, thus forming the posterior boundary of the posterior thyroid space. Its fibers converge on the thyrotracheo-esophageal area where they become dense and thick and fix the thyroid gland to this area. There is no cleavage plane at this point. This has been called the pedicle of the thyroid, and from here the fascia continues medially over the trachea and the larynx to join the pretracheal layer of the opposite side.
FIG. The pretracheal fascia. This fascia is a part of the general investing fascia; it arises from the deep surface of the sternocleidomastoid muscle. After passing in front of the carotid system, it attaches to the thyroid gland and then splits into 2 layers: an anterior prethyroid layer and a posterior pretracheal layer. The thyroid has been removed to show the distribution of the fascia. The inset shows the division of the fascia into 2 layers.
The vertical extent of the pretracheal fascia is from the hyoid bone above to the superior mediastinum below where it blends with the fibrous pericardium.
The suspensory ligaments of the thyroid gland are thickened portions of the pretracheal fascia that run from the upper and inner parts of the gland to the cricoid cartilage. The ligaments form a sling that anchors the gland to the larynx which must be severed before the thyroid can be mobilized properly.
DEEP LAYER (PREVERTEBRAL FASCIA)
The prevertebral fascia also arises from the general investing fascia and is much thicker than the pretracheal. It passes behind the carotid system and covers the muscles that are applied to the cervical vertebrae (longus colli, longus capitis, scalenus anterior, medial and posterior, etc.). It is attached to the base of the skull above and continues into the thorax where it blends with the anterior longitudinal ligament of the spine. The great vessels of the neck lie on this fascia, and the phrenic nerve and the anterior rami of the cervical nerves are behind it. As the roots of the brachial plexus and the subclavian artery pass under the scalenus anterior muscle they carry the prevertebral fascia with them into the axilla as the axillary sheath. BUCCOPHARYNGEAL FASCIA
The buccopharyngeal fascia is a layer of connective tissue that passes around the sides and the back of the pharynx
FIG. The buccopharyngeal fascia. (A) This fascia binds the upper part of the pharynx to the prevertebral fascia directly in the midline. (B) Acute retropharyngeal abscess involves the lymph glands in front of the prevertebral fascia and because of the attachment of the buccopharyngeal fascia presents to either side of the midline. (C) The chronic abscess, usually from tuberculosis of a cervical vertebra, is behind the prevertebral fascia and appears in the midline.
and binds the middle of the back of the pharynx to the prevertebral fascia. This anatomic fact aids in the diagnosis and the treatment of retropharyngeal abscesses. In the unilateral variety or acute retropharyngeal abscess, a group of inflamed lymph glands break down which lie in the interval between the prevertebral and the buccopharyngeal fasciae. They drain the nasopharynx and bulge on one side of the midline because of the midline attachment of the two fascia. The midline variety or chronic retropharyngeal abscess usually results from tuberculosis of a cervical vertebra and starts behind the prevertebral fascia. Should it bulge into the pharynx it would be centrally located; it may then travel laterally behind the prevertebral fascia and point at the posterior border of the sternocleidomastoid.
SUBMENTAL TRIANGLE The submental triangle has as its base the body of the hyoid bone and as its apex the symphysis of the mandible. It is bounded laterally by the anterior bellies of the digastric muscles. The roof of the triangle is made up of the investing layer of deep cervical fascia, and its floor is formed by the mylohyoid muscles with their median raphe. The triangle contains the submental lymph glands, which drain the superficial tissue below the chin, the central part of the lower lip, the adjoining gums, the anterior part of the floor of the mouth, and the tip of the tongue. The efferent vessels from these glands pass to join the submandibular (submaxillary) lymph glands. When they enlarge or become abscessed they are usually prevented from rising into the mouth by the mylohyoid muscles. Wide incisions may be made into this area because there are no important structures that can be injured. After incising the investing layer of deep cervical fascia, location of the digastric and the mylohyoid muscles will immediately orient the surgeon.
Anterolateral Region of the Neck
ANTERIOR TRIANGLE The anterior triangle of the neck is bounded in front by the midline of the neck, which extends from the symphysis of the mandible above to the sternal notch below; behind, by the anterior border of the sternocleidomastoid; above, by the lower border of the mandible and a line drawn backward from its angle to the posterior boundary. This triangle is subdivided into 3 subsidiary triangles by the anterior and the posterior bellies of the digastric and the superior belly of the omohyoid.
The digastric triangle is bounded by the anterior belly of the digastric in front, the posterior belly of the same muscle behind, and the border of the mandible above.
The carotid triangle is bounded by the superior belly of the omohyoid below, the sternocleidomastoid behind and the posterior belly of the digastric above.
The muscular triangle is bounded by the superior belly of the omohyoid above, the sternocleidomastoid below, and the midline of the neck in front.
Submental Triangle. That region of the neck which is bounded by the body of the hyoid bone below and the anterior bellies of the digastric on each side forms the submental triangle.
SUPERFICIAL STRUCTURES (SKIN, SUPERFICIAL FASCIA, PLATYSMA AND LYMPH NODES)
Skin. The skin of the neck is loosely attached, especially anteriorly. Since it is well supplied with blood vessels, it favors plastic surgery. The skin that covers the posterior region is very thick, adherent and contains numerous sebaceous glands, which explains the frequency of furuncles and carbuncles in this area.
Superficial Fascia. This fascia of the neck consists of fat and connective tissue. It is not clearly defined and is difficult to demonstrate.
Platysma Myoides. This rhomboidal muscle lies in the superficial fascia of the neck . It originates from the fascia of the pectoralis major and the deltoid and inserts into the lower border of the mandible; its fibers converge as they pass upward and medially. Some of the fibers reach the face and mingle with the risorius and other depressor muscles. Its posterior border is free, covers the lower anterior part of the posterior triangle and continues across the base of the jaw to the angle of the mouth. Its anterior border decussates behind the chin. Since it is a muscle of expression, it is supplied by the cervical branch of the facial nerve which reaches its deep surface. Branches of the anterior cutaneous nerve of the neck pierce it. In some individuals it is well developed and in others it is difficult to find. It is lacking in the midline of the neck; therefore, it cannot be sutured in this location. Between the muscle and the underlying superficial layer of deep cervical fascia lie the anterior and the external jugular veins and the cutaneous nerves of the neck. Incisions in the neck bleed freely before the deep fascia is cut, because the retraction of the divided platysma holds the cut veins open and prevents them from retracting. However, when the deep fascia is divided, the veins are able to retract, and most of the oozing stops.
Lymph Nodes. The external jugular lymph nodes are usually found as a cluster lying upon and near the external jugular vein as it approaches the region of the parotid gland. They are superficial to the superficial layer of the deep cervical fascia and, wheot diseased, are small or even absent. They receive lymph from the external ear in the parotid region and drain into the deep nodes which lie upon the carotid sheath beneath
FIG. The triangles of the neck.
FIG. The platysma muscle. A wedge of muscle has been cut out on the left to show the underlying nerves. The inset shows the true position of the platysma, in the superficial fascia.
the sternocleidomastoid muscle. Since they are on and not under the deep fascia, it is a safe and simple procedure to eradicate or incise them, but the position of the external jugular vein should be kept in mind.
NERVES
Four superficial nerves associated with the posterior border of the sternocleidomastoid muscle; they supply the skin of this region. They are derived from the anterior primary rami of the 2nd, the 3rd and the 4th cervical nerves through the branches of the cervical plexus, which lies under cover of the muscle.
Lesser Occipital. The lesser occipital nerve (2nd cervical) appears at the junction of the middle and the upper thirds of the posterior border of the sternocleidomastoid where it hooks around the accessory nerve; it passes upward and backward along the posterior border of that muscle to supply the skin over the lateral part of the occipital region.
Great Auricular. The great auricular nerve (2nd and 3rd cervicals) appears at a slightly lower level, runs parallel with the external jugular vein and enters the nuchal region posterior to the ear; it supplies the skin over the angle of the jaw, the parotid gland, the postero-inferior half of the lateral and the medial aspects of the auricle, and the skin over the mastoid region.
Anterior Cutaneous. The anterior cutaneous nerve (cutaneous colli, 2nd and 3rd cervicals) appears close to the great auricular nerve but runs transversely forward across the sternocleidomastoid and beneath the external jugular vein; it supplies the region about the hyoid bone and the thyroid cartilage.
Supraclavicular. The supraclavicular nerve (3rd and 4th cervicals) appears at a slightly lower level than the preceding ones. The anterior (medial) supraclavicular travels downward and medially across the lower part of the sternocleidomastoid; the middle (intermediate) runs across the clavicle, and the posterior (lateral) extends downward and laterally across the trapezius and the acromial end of the clavicle.
The last four cranial nerves, in their extracranial courses, are located in the region of the digastric muscle.
Vagus. The vagus (10th cranial) nerve leaves the skull through the jugular foramen and at its exit is closely related to the 9th, the 11th and the 12th nerves; the internal jugular vein lies posterior to it, and the internal carotid artery is anterior. In the neck the vagus supplies the alimentary and the respiratory tubes by means of its branches— the pharyngeal, the superior and the recurrent laryngeal.
Glossopharyngeal. The glossopharyngeal nerve (9th cranial) leaves the skull through the jugular foramen with the vagus and the accessory, but in its own sheath of dura mater. It descends between the internal jugular and the internal carotid vessels to the lower border of the stylopharyngeus around which it winds and then passes forward between the internal and the external carotid arteries. Its one motor branch supplies the stylopharyngeus muscle.
Spinal Accessory. The spinal accessory nerve (11th cranial) has a double origin: spinal and cranial. The spinal part arises from the upper 5 or 6 segments of the spinal cord, and the cranial is accessory through the vagus. It makes an abbreviated appearance in the carotid triangle between the digastric and the sternocleidomastoid muscles. As it enters the deep surface of the sternocleidomastoid about 2 inches below the tip of the mastoid process, it is surrounded by lymph glands and is accompanied by the sternocleidomastoid branch of the occipital artery. It appears about the middle of the posterior border of the sternocleidomastoid muscle and here again is surrounded by lymph glands. The accessory nerve supplies the sternocleidomastoid and the trapezius; its cervical branches are entirely sensory.
Hypoglossal. The hypoglossal nerve (12th cranial) is the motor nerve of the tongue. It emerges from the skull through the anterior condylar (hypoglossal) canal in the occipital bone and is in close contact with the 9th, the 10th and the 11th cranial nerves. It lies between the internal jugular vein and the internal carotid artery and, as it descends, is closely related to the vagus until it appears at the lower border of the posterior belly of the digastric. Here it turns forward and medially and crosses, in turn, the internal
FIG. The 4 superficial nerves of the neck. These are cutaneous nerves and all ot them are related to the posterior border of the sternocleidomastoid muscle. The inset shows the plan of the veins in this region.
carotid, the occipital and the external carotid arteries and the loop of the lingual artery. As it crosses the lingual artery, the hypoglossal nerve is crossed superficially by the common facial vein, passes deep to the posterior belly of the digastric and the submaxillary gland and enters the submandibular region where it is distributed to the muscles of the tongue. As the nerve continues forward, it comes to lie superficial to the hyoglossus muscle which separates it from the lingual artery, then continues in an intermuscular cleft between the hyoglossus and the mylohyoid to the muscles of the tongue. The ascending branch of the hypoglossal nerve leave its parent trunk where it bends forward to cross the carotid vessels. The descending branch continues downward on the surface of the internal and the common carotid arteries and is imbedded in the anterior wall of the carotid sheath. From its lateral side it is joined by the descending cervical nerve (2nd and 3rd cervicals) which arises from the cervical plexus, and the nerve loop so formed constitutes the ansa hypoglossi. Branches from this ansa are distributed to the sternohyoid, the sternothyroid and both bellies of the omohyoid. The thyrohyoid receives its own nerve from the first cervical via the hypoglossal.
Cervical Plexus. This plexus should not be confused with the cervical sympathetic groups. The plexus lies on the scalenus medius and the levator anguli scapulae under cover of the sternocleidomastoid muscle. It is formed by the upper 4 cervical nerves, all but the first of which divides into 2 parts. A branch from each nerve joins the superior cervical ganglion. These nerves are combined in irregular series of loops under cover of the sternocleidomastoid. The roots of the plexus lie deep to the prevertebral fascia and are frequently injured in radical neck surgery. The terminal branches pierce the fascia and continue to
FIG. The last 4 cranial nerves in their extracranial courses. These nerves are closely related to the posterior belly of the digastric muscle. The formation of the ansa hypoglossi is also shown.
the muscles which they supply and the nerves with which they connect. The superficial cutaneous branches radiate from the plexus and appear in the supraclavicular region as they wind around the posterior margin of the sternocleidomastoid muscle.
Phrenic Nerve. Of the muscular or deep branches, the phrenic is the most important. It is derived from the 4th cervical, but receives additional fibers from the 3rd and the 5th. It passes downward in the neck and lies deep to the prevertebral fascia, traveling on
FIG. The cervical sympathetics. This group consists of 3 ganglia with their connecting branches. The ganglia are known as superior, middle and inferior and have been called carotid, thyroid and vertebral, respectively, from their almost constant association with these arteries. The inset shows these relationships. The cervical plexus should not be confused with the cervical sympathetic group. The plexus is formed by the upper 4 cervical nerves and lies on the scalenus medius muscle.
the anterior scalene muscle; it enters the thorax at the root of the neck on its way to the diaphragm.
Superficial Branches of the Cervical Plexus. These branches, all cutaneous, are the cutaneous colli, the lesser occipital, the great auricular and the descending supraclavicular nerves. The deep branches are muscular and divide into anterior and posterior branches. The anterior branch supplies the thyrohyoid, the geniohyoid, the rectus capitus lateralis, the rectus capitis anterior, the longus capitis, the longus colli, the scalenus anterior and the intertrans-
FIG. Phrenic avulsion. (A) the incision starts at the posterior border of the sternomastoid muscle, one fingerbreadth above the clavicle. (B) The deep cervical fascia is incised, and the subfascial fat, which is an important guide, is identified. The transverse cervical and suprascapular arteries clamp the phrenic nerve onto the scalenus anterior muscle. (C) The phrenic nerve is avulsed.
versalis. The posterior branch supplies the sternocleidomastoid, the levator scapulae, the trapezius and the scalenus medius muscles. Communicating branches also are found which travel to the sympathetics and the hyoglossal muscle.
Cervical Sympathetic. This group consists of 3 ganglia with connecting branches which form a chain lying behind the carotid sheath and upon the prevertebral fascia. It extends from beneath the mastoid process to the 1st rib. The ganglia are known as the superior, the middle and the inferior and have been called, respectively, carotid, thyroid and vertebral from their almost constant association with these arteries. The superior or carotid is the largest ganglion in the neck. It lies in front of the transverse processes of the 2nd and the 3rd cervical vertebrae on the longus capitis and behind the carotid sheath. It is fusiform in shape and sends a branch downward to connect with the middle ganglion. The middle or thyroid ganglion is the smallest of the 3, and some authors state that it is inconstant or absent. This error may be due to the fact that the ganglion sometimes occupies a lower position, nearer the inferior ganglion of which it has been considered a part. It lies on a level with the 6th cervical vertebra in front of or behind the inferior thyroid artery. The inferior or vertebral ganglion is next
in size to the superior. It is found behind the vertebral artery, between the neck of the 1st rib and the transverse process of the 7th cervical vertebra. At times it unites with the first thoracic sympathetic ganglion to form the stellate ganglion. Since it is beneath the vertebral artery, just as the latter is given off from the subclavian, it makes surgical approach to the ganglion difficult. Some of the fibers that connect the middle with the inferior cervical ganglion descend in front of the subclavian artery and then upward behind it to form the so-called ansa subclavia.
SURGICAL CONSIDERATIONS
Phrenic Avulsion. The phrenic nerve is usually described as originating from the 4th
cervical; however, it has been found orig nating from the 1st, the 2nd, the 3rd, the 5th and the 6th cervicals and the 1st dorsal nerves. Accessory phrenics are present at times, and for this reason the operation of vulsion is to be preferred. Fibers of the 5th cervical traveling with the nerve to the subclavius muscle are the most common varieties of accessory phrenics found. During avulsion the phrenicopericardial vessels may be torn, producing an internal hemorrhage. An incision about 2 inches long is made, starting at the posterior border of the sternocleidomastoid muscle and is placed about a fingerbreadth above the clavicle. If greater exposure is desired, a longitudinal incision about 3 to 4 inches long is placed along the posterior border of the sternocleidomastoid muscle. The incision is deepened through the platysma where the superficial cervical nerve and the external jugular vein come into view; these may be divided or retracted. The posterior border of the sternocleidomastoid is identified and cleansed, as is the belly of the omohyoid. The deep cervical fascia which forms a cover for the scalenus anterior is identified and incised, and the underlying adipose tissue is noted. This fat is an important guide, since the muscle is not immediately visualized when the cervical fascia has been severed. The subfascial fat is dissected free, and the scalenus anticus is exposed. As the muscle is cleared, the phrenic nerve appears toward its medial aspect as a thin, white cord running downward and slightly toward the midline. The transverse cervical and suprascapular arteries clamp the phrenic nerve down onto the scalenus anterior in this fatty tissue. These vessels should be looked for and retracted, since they might cause annoying hemorrhage and make exposure difficult. Pinching the phrenic produces pain in the neck, the shoulder or the arm and dilation of the corresponding pupil. After proper identification, the nerve can be divided, resected, injected or avulsed by slowly winding the distal end on a hemostat. The thoracic duct should be protected while operating on the left phrenic nerve.
Stellate Ganglionectomy. This is particularly useful in dealing with amputation stump neuralgia, painful traumatic arthritis and causalgia when these are associated with vasospasm which responds to diagnostic procaine injections. It has also been utilized in angina pectoris, bronchial asthma and hyperhidrosis. Many technics have been used in cervical sympathectomies and ganglionectomies, but the following is one of the most common methods employed. A transverse incision is made about a fingerbreadth above the clavicle and is carried laterally
FIG. The 4 infrahyoid muscles: (A) the 2 superficial muscles are seen on the right side and the 2 deeper ones on the left; (B) the nerve supply.
side. Sibson’s fascia, which attaches the apex of the pleura to the posterior part of the 1st rib, is cut. The entire apical pole can then be freed by blunt dissection to about the level of the 3rd rib. This should permit visualization of the inferior cervical and the first thoracic ganglia. It should be remembered that this may appear as a double ganglion, which is shaped like a dumb-bell with an isthmus, or may appear as a single mass. Its lower part lies in front of and against the head of the 1st rib; its upper pole is connected with the lower trunk of the brachial plexus by fine rami which give it a star-shaped appearance, hence the name “stellate.” It is dissected free, and the nerve chain is followed down as far as the 3rd thoracic ganglion. The incision is closed in layers.
MUSCLES
Infrahyoid. The infrahyoid muscles have been referred to as the depressors of the larynx and also as the “strap” or “ribbon” muscles. The 4 muscles making up this group are the sternohyoid, the omohyoid, the sternothyroid and the thyrohyoid. The first two lie side by side and cover the other two. All are supplied by branches of the anterior rami of the 1st, the 2nd and the 3rd cervical nerves by means of the hypoglossal nerve and the ansa hypoglossi which approach the muscles from the lateral side. The nerves pass between the superficial and the deep muscles and enter their opposed surfaces.
Sternohyoid. This muscle arises from the posterior surface of the manubrium sterni and the adjoining part of the clavicle, continues upward and medially and inserts into the medial part of the lower border of the body of the hyoid bone. At its origin it is separated from its fellow of the opposite side by an interval of cm., but as they ascend they gradually converge so that at the point of insertion both muscles lie in contact with each other. The interval between the two muscles is filled by the pretracheal fascia. Contraction of this muscle depresses the hyoid bone.
Omohyoid. The omohyoid muscle consists of an inferior belly, an intermediate tendon and a superior belly. It lies in the same plane as the sternohyoid. The inferior belly arises from the upper border of the scapula and the suprascapular ligament, crosses the posterior triangle of the neck and passes deep to the sternocleidomastoid and ends as the intermediate tendon. It lies on the surface of the carotid sheath and is bound to the clavicle by the deep cervical fascia which forms a fascial sling. Its tendon gives origin to the superior belly which passes upward and medially superficial to the common carotid artery and along the lateral border of the sternohyoid. It becomes inserted into the lower border of the body of the hyoid bone. The omohyoid abruptly bends away from the sternohyoid below the level of the cricoid cartilage. Unlike the digastric, the two bellies of the omohyoid are supplied by the same nerve, since the inferior belly is a backward extension of the superior. Its action depresses the hyoid bone and draws it backward and laterally. The two deeper muscles, thyrohyoid and sternothyroid, are divided into a muscle above and one below the oblique line of the thyroid cartilage where both attach.
The sternothyroid is of considerable surgical importance. It is perhaps the most important surgical landmark in thyroid surgery and, if identified properly, can aid in finding the correct cleavage plane. It must be emphasized that a distinct cleavage plane exists between the sternohyoid and the sternothyroid muscles, and very often the surgeon believes that he has cut both muscles when in reality only the more superficial sternohyoid has been severed. If the thyroid gland is enlarged, the sternothyroid becomes so thin that it is noUclearly visualized. If this should occur, then the true capsular structures and the cleavage planes are lost, and the operation proceeds with great difficulty and much hemorrhage. The muscle arises from the posterior aspect of the manubrium sterni, extends upward deep to the sternohyoid and covers the lobe of the thyroid gland. It is inserted into the oblique line on the lamina of the thyroid cartilage. The lower border converges on its fellow as it descends until their medial borders just meet at the center of the manubrium. Its contraction depresses the larynx.
The thyrohyoid muscle is a short, quadrilateral structure which appears to be a con-
tinuation of the sternothyroid. It arises from the oblique line on the thyroid cartilage, passes upward and is inserted into the lower margin of the hyoid bone. The muscle is fairly thick, covers the thyrohyoid membrane and projects laterally to the omohyoid. It depresses the hyoid bone, but when the bone is fixed by the suprahyoid muscles, it acts as an elevator of the larynx. The digastric muscle constitutes another important surgical landmark and guide in the upper part of the neck. Its name suggests that it has 2 bellies that are connected by a common tendon. The anterior belly runs forward, medially and upward from the common tendon to attach to the lower border of the mandible near the midline. It is placed on the surface of the mylohyoid muscle and is partly overlapped by the submaxillary gland. The posterior belly arises from the mastoid part of the temporal bone and is covered by the mastoid process and the sternocleidomastoid muscle, but as it passes downward, forward and medially it becomes visible. It crosses superficially to the internal jugular vein, the accessory, the vagus and the hypoglossal nerves, the occipital, the internal and the external carotids and the facial (external maxillary) arteries. The common or so-called intermediate tendon is attached to the body of the hyoid by a pulleylike band of fascia. This tendon perforates the stylohyoid muscle, lies on the hyoglossus muscle and is overlapped by the submaxillary gland. The latter is a good guide to the intermediate tendon, and the intermediate tendon in turn is a good guide to the hyoglossus muscle. The nerve supply of the muscle is derived from two sources. The posterior belly is supplied by the facial nerve as it leaves the stylomastoid foramen, and the anterior belly by the nerve to the mylohyoid from the trigeminal nerve. Therefore, the posterior belly receives its nerve supply from the 7th cranial; and the anterior belly, from the 5th cranial nerve.
VESSELS AND CAROTID SHEATH
The general investing layer of the deep cervical fascia gives rise to 2 sheaths which originate from the deep surface of the sterno-
FIG. The carotid arteries. The internal carotid is more posterolateral than internal, and as it ascends it lies medial to the external carotid. The external carotid has 8 branches, 5 of which are below and 3 above the digastric muscle.
cleidomastoid. These 2 offshoots are the pretracheal and the prevertebral layers. Between them and near their origin are found the common carotid artery, the internal jugular vein and the vagus nerve. The fascia immediately surrounding these structures, the pretracheal in front and the prevertebral behind, forms the carotid sheath, which extends from the base of the skull to the root of the neck. The sympathetic trunk is imbedded in its posterior wall, the descendens hypoglossi in the anterior wall, and the descendens cervicalis, the cervical branches of the vagus and the internal jugular vein pierce it. Although the structures are surrounded by this tubelike fascia, they also are imbedded in fibrous tissue that is derived from it so that each structure has its own coat. The vein is external to the artery and almost entirely covers it. The sheath is applied to the side of the cervical viscera, namely, the esophagus, the pharynx and the thyroid gland.
Carotid Arteries. The common carotid artery arises differently on the two sides: the right arises as a terminal branch of the innominate behind the sternoclavicular joint; the left originates in the thorax from the arch of the aorta, passes upward and to the left and enters the neck behind the left sternoclavicular joint. This is the largest artery in the neck; and as it passes from behind the sternoclavicular joint, it runs upward and backward under cover of the anterior border of the sternocleidomastoid muscle in the direction of the mandible. When it reaches the level of the upper border of the thyroid cartilage it forms a dilation known as the carotid bulb and then divides into its 2 terminal branches: the internal and the external carotid arteries. The carotid body and the carotid sinus are 2 sensory structures which are frequently confused; they are associated with the region of the carotid bifurcation. The carotid body is a small flattened structure measuring about 2.5 by 6 mm. It is usually found on the posteromedial side of the common carotid artery where it is held firmly in place by connective tissue. It contains numerous nerves and nerve endings and at one time was regarded as part of the chromaffin system. It does not secrete epinephrine, and its cells do not have a chromaffin reaction. Its nerve supply is not via the sympathetic system. The carotid body represents a specialized sensory organ (vascular chemoreceptor) which responds to chemical changes in the blood and thereby affects cardiovascular output and respiration. Hypoxia and anoxia stimulate this body, resulting in an increase in blood pressure, cardiac rate and respiratory movements. On occasion, tumors arise in the carotid body, which have been referred to as “glomus” tumors. This is a misnomer, since it is not a tumor of arteriovenous origin. The removal of carotid body tumors may be extremely difficult and associated with morbidity and/or mortality. The carotid sinus is usually located at the base of the internal carotid artery and is nerve.
FIG. The carotid sinus, the carotid body, and their relationships to the glossopharyngeal
composed of numerous and complicated sensory nerve endings. In contrast with the carotid body (chemoreceptor), the carotid sinus is a pressoreceptor. Its nerve endings are stimulated by pressure as by the pressure of blood itself. Stimulation of this sinus causes a reduction of blood pressure and a slowing of the heart rate. At times this sinus becomes unduly sensitive to pressure so that a mere turning of the head may drop the blood pressure, slow the heart and produce loss of consciousness. Denervation of the sinus may abolish this so-called carotid sinus syndrome. The nerve to both the carotid body and the carotid sinus is the intercarotid nerve (Hering); it arises from the glossopharyngeal nerve. Some authorities are of the opinion that this nerve supply may be connected with the vagus, the hypoglossal or the superior cervical ganglion. Throughout the course of the common carotid artery it is imbedded with the internal jugular vein and the vagus nerve, in the connective tissue that constitutes the carotid sheath. The vein lies on the lateral side of the artery and when full of blood overlaps it anteriorly. The vagus nerve lies posteriorly between the artery and the vein. Usually the only branches of the common carotid are its terminal ones, but occasionally, when its bifurcation is at a higher level, the ascending pharyngeal or the superior thyroid may arise from it. Anteriorly, in addition to the superficial structures, this artery is covered by the anterior border of the sternocleidomastoid muscle. Between the muscle and the artery in the lower part of the neck the following structures intervene: the superior belly of the omohyoid, the sternohyoid and the sternothyroid muscles. In the upper part of its course the descending ramus of the hypoglossus and the ansa hypoglossi are imbedded in the anterior wall of the sheath, and the common facial vein usually crosses the artery at its termination. Posteriorly, the artery is related to the anterior tubercles of the transverse processes of the lower 4 cervical vertebrae and the muscles that attach here, namely, the scalenus anterior and the longus capitis. It is separated from these structures by the prevertebral fascia and the sympathetic trunk. In the lower part of the neck it lies in front of the vertebral artery as it ascends to the foramen and the transverse process of the 6th cervical vertebra and in front of the inferior thyroid artery, which arches medially to the thyroid gland. On the left side the thoracic duct crosses behind the vessel and below the inferior thyroid artery. Medially, it is related to the inferior constrictor muscle of the pharynx and the thyroid gland. The lobe of the thyroid either lies medial to the artery separating it from the esophagus, the pharynx, the trachea and the larynx or forms a direct anterior relation. Laterally, it is related to the internal jugular vein and the vagus nerve.
The internal carotid artery is the larger of the 2 terminal branches of the common carotid. It is distributed to the brain and to the eye and its appendages. From its origin at the upper border of the thyroid cartilage it passes to the carotid canal of the temporal bone. It turns forward in the cavernous sinus, perforates the dura mater on the inner side of the anterior clinoid process and divides into the anterior and the middle cerebral arteries. Below the posterior belly of the digastric the artery is overlapped by the anterior border of the sternocleidomastoid and the more superficial structures; the hypoglossal nerve, the occipital artery and the common facial vein are interposed between it and the muscle. Above, the artery ascends under cover of the posterior border of the digastric and the stylohyoid and is crossed by the posterior auricular artery. It passes beneath the styloid process and the stylopharyngeus muscle. These 2 structures are placed between the artery and the parotid gland in which the external carotid artery and the posterior facial vein are imbedded. The internal carotid has no branches in the neck. It may be difficult to distinguish between the internal and the external carotid arteries. Even in a well-planned operation for ligation, one has been mistaken for the other; hence, the following points should be noted: the internal carotid furnishes no branches in the neck, but the external has 3 anterior branches; the vessel is not really internal but at its origin is posterolateral to the external vessel; as it ascends it passes to the medial side of the external carotid toward the lateral wall of the pharynx.
The external carotid artery is the smaller of the 2 terminal branches of the common carotid and extends from the upper part of the thyroid cartilage to the neck of the mandible where it divides into its 2 terminal branches—the superficial temporal and the maxillary (internal) arteries. This carotid has been called “external,” not because of its location, which is really internal and superficial to the internal carotid, but because of the fact that it is distributed to parts outside of the skull. Near the angle of the jaw it is crossed by the posterior belly of the digastric and the stylohyoid muscles. Above this it is at first deep to and then enclosed by the substance of the parotid gland where it terminates opposite the neck of the mandible by dividing into its 2 terminal branches. In its short course before entering the substance of the parotid, it is applied to the inferior and the middle constrictor muscles. The vessel has 8 branches: 5 below the digastric muscle and 3 above it.The 5 branches below the digastric muscle are:
1. The superior thyroid artery, which arises from the anterior aspect of the external carotid near its origin. It passes downward and forward under cover of the omohyoid, the sternohyoid and the sternothyroid muscles, parallel with but superficial to the external laryngeal nerve. It reaches the upper pole of the thyroid gland to which it is distributed. Its branches are the infrahyoid, the superior laryngeal, the sternocleidomastoid, the cricothyroid, the isthmic, the glandular and the muscular.
2. The lingual artery arises opposite the greater cornu of the hyoid bone, makes an upward loop, disappears under cover of the hyoglossus muscle and enters the submandibular (submaxillary) region. The loop of this artery is crossed superficially by the hypoglossal nerve.
3. The facial (external maxillary) artery arises near the angle of the mandible, is directed upward and forward on the superior constrictor muscle, beneath the digastric; it continues in a groove on the deep surface of the submandibular gland to the body of the mandible and ascends to the face, anterior to the masseter muscle.
4. The ascending pharyngeal artery arises from the deep aspect of the external carotid close to its origin and continues upward, medial to the internal carotid on the side wall of the pharynx. It is usually small and supplies the pharynx, the soft palate and the meninges.
5. The occipital artery arises from the posterior aspect of the external carotid opposite the facial and continues upward and backward deep to the posterior belly of the digastric. It is crossed by the transverse part of the hypoglossal nerve at its origin, follows the posterior belly of the digastric and is in contact with the skull medial to the mastoid notch, lying deep to the process in the muscles that attach to it. It anastomoses with the deep cervical branch from the costocervical trunk and thus forms a link between the subclavian and the carotid systems. The branches of the external carotid artery above the digastric muscle are 3 iumber. The posterior auricular artery generally arises at or above the upper border of the muscle and in the parotid region. It becomes superficial as it crosses the base of the mastoid process and ascends behind the auricle. It supplies the area of the auricle on the back of the scalp. The 2 terminal branches of the carotid, the superficial temporal and the “internal” maxillary, have been discussed elsewhere. The superficial relations of the external carotid artery are: in the carotid triangle the vessel is covered by skin, superficial fascia, platysma, branches of the anterior cutaneous nerve of the neck, the cervical branch of the facial nerve and the deep fascia. Beneath the deep fascia, the artery is crossed by the common facial and lingual veins and the hypoglossal nerve. At the upper part of the triangle the anterior branch of the posterior facial vein crosses the artery. After leaving the carotid triangle, the vessel is partially covered by the angle of the mandible and is crossed by the posterior belly of the diagastric and the stylohyoid muscles. Within the substance of the parotid gland the posterior facial vein is superficial to the artery, and both of these vessels are crossed in turn by branches of the facial nerve. In its entire course the vessel is accompanied by numerous sympathetic ganglia which constitute the external carotid plexus.
Collateral anastomoses between the internal and the external carotids are usually adequate to maintain circulation after ligation of either of the vessels. Many anastomotic connections exist between the arteries of the ophthalmic region of the internal carotid and the facial region of the external. Communications exist between the external carotid artery and the thyrocervical trunk through the superior thyroid branch of the former and the inferior thyroid branch of the latter. A communication between the vertebral and the internal carotid arteries via the posterior communicating artery of the circle of Willis is also present. Other communications between the lingual, the facial, the occipital, the posterior auricular and the ascending pharyngeal arteries connect the external carotids of the 2 sides. The internal carotid arteries communicate across the base of the brain by the anterior communication artery and with the basilar trunk. When the common carotid is ligated, circulation is not interfered with anatomically or clinically unless the anastomotic paths are disturbed
by vascular degenerative changes due to age or other pathologic processes.
External and Internal Jugular Veins. The external jugular vein varies in size. It is formed below the lobule of the ear by the union of the posterior auricular vein with a branch of the posterior facial. It begins at the lower part of the parotid gland, runs almost vertically downward, crosses the sternocleidomastoid muscle obliquely, and in the angle between the
FIG. Lateral view of the veins of the neck: (A) the platysma has been reflected to show the external jugular vein, and the sternocleidomastoid has been cut to show the internal jugular; (B) tributaries of the internal jugular vein.
clavicle and the posterior border of that muscle pierces the deep cervical fascia to which it is firmly bound; it then joins the subclavian vein. It lies upon the superficial layer of deep cervical fascia, beneath the platysma muscle, and at times may be absent or very small. It is so closely associated with the platysma that when the latter is reflected, the vein remains attached to it. If one external jugular is large the other is small; and if both are large, then the internal jugulars are correspondingly small. The external communicates with the internal jugular via a branch which turns around the anterior border of the sternocleidomastoid. At times, it receives a posterior jugular vein from the back of the neck. At its termination the external jugular is joined by the transverse cervical, the suprascapular and the anterior jugular veins. The internal jugular vein begins at the jugular foramen about 1/2 inch below the base of the skull, as a continuation of the sigmoid (transverse) sinus. It passes downward and forward through the neck and ends behind the upper border of the sternal end of the clavicle where it meets the subclavian and forms the innominate vein. It is dilated markedly at its origin, forming the superior bulb that lies in the jugular foramen and the fossa. This bulb is larger on the right side because the superior sagittal sinus usually turns to the right. The inferior bulb is a dilation of the vein below a bicuspid valve which is situated about 1/2 inch above the clavicle. The junction of the internal jugular and the subclavian veins is separated from the lower part of the sternoclavicular joint by the 2 infrahyoid muscles. The tributaries of the veins in this region are:
1 The inferior petrosal sinus, which helps to drain the cavernous sinus and leaves the skull through the anterior part of the jugular foramen to join the upper end of the internal jugular.
2. The pharyngeal veins from the plexus on the side of the pharynx pass either superficially or deeply to the internal carotid artery and join the internal jugular vein in the upper part of the neck.
3. The common facial vein is the largest and most important tributary of the internal jugular. It is formed by the union of the anterior and the posterior facial veins and continues downward and backward just above the level of the upper border of the thyroid
FIG. The anterior, the external and the internal jugular veins. The sternocleidomastoid
muscle has been cut and reflected on the left side.
FIG. Ligation of the common carotid artery: (A) ligation above the omohyoid muscle; this is the site of choice; (B) ligation below the omohyoid muscle.
cartilage. It passes superficially to the hypoglossal nerve as that structure crosses the loop of the lingual artery. At times it receives the thyroid and the lingual veins and then is referred to as the “thyrolingual facial trunk.”
4. The lingual vein, when it does not form a tributary of the common facial, enters the internal jugular opposite the greater cornu of the hyoid bone.
5. The superior thyroid vein ascends from the upper pole of the thyroid gland in company with the corresponding artery. At the pole there are numerous small tributaries of this vein which form a trunk at a higher level. It crosses superficially to the common carotid artery and joins either the common facial or the internal jugular vein. 6. The middle thyroid vein passes laterally and deeply to the infrahyoid muscles. It crosses superficially to the common carotid artery and ends in the internal jugular at the level of the cricoid cartilage. The internal jugular vein is enclosed in the carotid sheath. Its uppermost part lies behind the internal carotid artery and posterolateral to the last 4 cranial nerves. As the vein descends, it lies laterally to the common carotid and overlaps it; hence, in exposing the artery its sheath should be opened toward the inner side to avoid injuring the vein. Superficial Relations of the Internal Jugular Vein. These relations are the most complicated and the most important surgically. Throughout the greater part of its course the internal jugular lies under the sternocleidomastoid muscle, but in its extreme upper portion it is deep to the parotid gland. lnjeriorly, the infrahyoid muscles are situated between the vessel and the sternocleidomastoid. In its upper part it is separated from the parotid gland by the styloid process, the stylopharyngeus and the stylohyoid muscles and the posterior belly of the digastric. In this region it is crossed superficially by 2 arteries and a nerve (posterior auricular and occipital arteries and accessory nerve). At a lower level it is crossed by the sternocleidomastoid branch of the occipital artery. After leaving the parotid and the digastric at the upper angle of the carotid triangle, it disappears under the sternocleidomastoid but is separated from the muscle by many structures, namely, numerous lymph glands along its entire course, the descendens cervicalis nerve at the level of the thyroid cartilage, the sternocleidomastoid branch of the superior thyroid artery, the intermediate tendon of the omohyoid at about the level of the cricoid cartilage and, lastly, the sternohyoid and the sternothyroid muscles. Medially, the vein is related to the vagus nerve and the common carotid artery below, and to the 9th, the 10th the 11th and the 12th cranial nerves and the internal carotid artery above. Posteriorly, as the vein descends, it crosses the transverse process of the atlas and lies lateral to the tips of the lower transverse processes. In succession, it rests on the levator scapulae, the scalenus medius and the scalenus anterior muscles and is separated from them by the carotid sheath and the prevertebral fascia. The latter-named fascia is situated between the vein and the loops of the cervical plexus above and the phrenic nerve below.
SURGICAL CONSIDERATIONS
Ligations of Carotid Arteries and Internal Jugular Vein. The indications for ligation of the common carotid artery are wounds of the carotid artery or its branches, aneurysms, angiomas, inoperable tumors of the face, the neck and the skull, hemorrhage from distal branches and at times hydrocephalus and epilepsy. Ligation of the common carotid artery can be dangerous, especially in elderly people, since it may be followed by diplopia, blindness, convulsions, coma, hemiplegia or death. The point of election is above the omohyoid muscle; however, ligation below may be necessary in injuries of the artery. Collateral circulation takes place by means of the communications between the carotids of the 2 sides, both inside and outside the skull, and by the enlargement of branches of the subclavian artery. The chief communications outside the skull are the superior thyroid above with the inferior thyroid below, and the descending branch of the occiptal above with the
FIG. Ligation of the external carotid artery; the usual site is between the superior thyroid and the lingual arteries.
deep cervical and the ascending branch of the transverse cervical below. Within the skull the vertebral artery compensates for the carotid. In ligation above the omohyoid, the head is rotated toward the opposite side, and at the anterior border of the sternocleidomastoid muscle a 3-inch incision is made, the center of which is placed at the level of the cricoid cartilage. Superficial vessels are ligated; if necessary, the anterior and the external jugular veins are tied and divided. The deep fascia is severed; the sternocleidomastoid is retracted in an outward direction. The omohyoid muscle is exposed, and the carotid tubercle is felt where it lies in the angle between the sternocleidomastoid and the omohyoid. Pulsations of the artery can be felt in this angle. The jugular vein lies to the lateral side of the artery and overlaps it; the superior thyroid, the lingual and the facial veins may cross the artery at its upper end, and it may be necessary to ligate them. Some authorities believe that the internal jugular vein should also be ligated. The descending branch of the hypoglossal nerve may be identified on the anterior aspect of the carotid sheath and it is exposed and displaced medially. If the omohyoid muscle interferes with exposure or ligation, it may be severed or retracted in a downward direction. The sheath is opened to the inner side, and the artery is exposed. A ligature should e passed from without inward, keeping close to the artery, especially in back, so that the vagus nerve is not included in the ligature. Ligation below the omohyoid is much more difficult and is done only in case of necessity. The skin incision is longer and is usually extended to the jugular notch. If the sternocleidomastoid protrudes, it may be detached in the region of its sternal or clavicular head after severing the superficial layer of deep cervical fascia. The ribbon muscles that cover the thyroid gland are exposed, and the lateral margin of the sternothyroid is retracted medially with the thyroid and the trachea which lie behind it. The middle layer of deep cervical fascia, forming a sheath for the omohyoid muscle, is incised along the inferior margin of the muscle; this space reveals a few thyroid veins which usually require ligation. The inferior thyroid artery, passing beneath the carotid sheath, can usually be spared. The internal jugular vein is retracted laterally, the artery is freed, and a ligature is passed around it. If one hugs the artery, the recurrent laryngeal nerve can be avoided.
Ligation of the external carotid artery ) is indicated for wounds, aneurysms, as a palliative measure for malignant growths, and as a preliminary step to operations in the field supplied by its branches. After ligation below the digastric muscle, the collateral circulation is brought about by the inferior with the superior thyroid arteries, the deep cervical from the costocervical with the occipital, the transverse cervical with the occipital, branches of the 2 vertebrals, and branches of the 2 internal carotids through the circle of Willis. The usual site of ligation is between the superior thyroid and the lingual trunks, but it may be performed proximally to the superior thyroid. Since the latter vessel may arise from the common carotid, it is wise to expose the origin of both carotids. A skin incision is made, extending for about 3 inches from the angle of the jaw to the upper border of the thyroid cartilage, in front of the anterior border of the sternocleidomastoid muscle. Skin, platysma and superficial fascia are divided, exposing the anterior border of the sternocleidomastoid. Since the common facia] and lingual veins often cross the operative field, they are sought, ligated and divided. The superficial layer of deep cervical fascia is incised to mobilize the sternocleidomastoid muscle which is drawn backward. The carotid sheath is exposed and opened. In the connective tissue of the sheath the descending branch of the hypoglossal nerve is seen and is displaced medially, and the internal jugular vein is retracted laterally. Between them the bifurcation of the common carotid artery can usually be seen. Since the first part of the external carotid lies medial to the internal, the 2 vessels may be mistaken unless it is remembered that the external carotid is the only vessel that gives off branches. After the latter is exposed, it is ligated on a level with the greater cornu of the hyoid bone. It is best to pass the ligatures from the internal carotid side and to guard against including the descending hypoglossal nerve as well as the superior laryngeal nerve. The wound is closed in layers.
Ligation of the internal carotid artery has been done for wounds, aneurysms or pulsating exophthalmus due to an arteriovenous aneurysm between the artery and the cavernous sinus. Collateral circulation takes place through the circle of Willis. The internal carotid, running to the base of the occiput without giving off any lateral branches, can be exposed in its lower part in the same manner described for the external carotid artery. However, if it must be ligated near the base of the skull, the operation is a most extensive one, since exposure must take place above the posterior belly of the digastric, and here the vessel lies very deep. The internal carotid artery is identified near the bifurcation of the common carotid and then traced upward. The digastric muscle is retracted upward, and the external carotid inward. The ligature is passed from without inward, avoiding the internal jugular vein, the vagus nerve and the sympathetic trunk. Some authorities advise primary placement of a ligature around the common carotid to be used only in case of absolute necessity.
Ligation of the internal jugular vein has been resorted to in such conditions as transverse sinus thrombosis to prevent extension of infection into the general circulation. In its lower portion the vein is found quite easily, but identification becomes more difficult as it travels cephalad, since its tributaries become more numerous. The ligation of one or both jugular veins has been carried out without any appreciable difficulty. The vein may be found readily by incising along the anterior border of the sternocleidomastoid muscle; it is the most superficial structure in the carotid sheath.
Obstructing lesions in vessels supplying the brain may be associated with episodes of syncope and/or transient neurologic symptoms. Corrective or palliative procedures are now available to correct such difficulties associated with major or with “little” strokes. When obstruction of the internal carotid artery has been demonstrated, a bypass graft may be indicated. Another method of correcting these problems is removal of the obstructing agent (thromboendarterectomy) and widening of the vessel lumen by inserting an elliptical patch.
THYROID GLAND
Embryology. At the junction of the posterior third with the anterior two thirds of the tongue, the foramen caecum is noted as a small depression. From this site at an early stage of fetal life, a solid column of cells grows downward, becomes canalized and forms the thyroglossal duct, from which the thyroid gland is formed. The duct passes down exactly in the midline between the genioglossi muscles as far as the upper border of the thyroid cartilage, where it turns to one or the other side of the midline. From this point on its course is represented by the pyramidal lobe. The question whether the thyroglossal duct passes in front of, through, or behind the body of the hyoid bone seems to have been answered by Frazer who has shown that it is placed in front of the bone and then takes a recurrent course up behind the hyoid before continuing downward. For this reason many advocate removal of the midportion of the hyoid to make certain that the entire tract is eliminated. If the duct remains open after birth, thyroglossal cysts develop either above the thyroid cartilage where they are usually centrally placed, or below the cartilage where they are usually found to the left of the midline. Since the thyroglossal duct never opens onto the surface of the neck at any stage of its development, congenital thyroglossal fistula is impossible. However, fistulae do occur as a result of bursting or opening of a thyroglossal cyst onto the surface. Accessory thyroid glands may occur anywhere along the line of the duct and are sometimes found at the back of the tongue (lingual thyroids).
Thyroid Gland Proper. The adult thyroid is a ductless gland. It is a highly vascular, solid organ related to the pretracheal fascia, that binds it to the larynx and causes it to rise and fall during the act of swallowing. It possesses its own true fibrous capsule, which is continuous with the stroma of the gland. The thyroid consists of a pair of lateral lobes which are joined across the median line by the isthmus. Each lateral lobe extends from the middle of the thyroid cartilage to the 6th tracheal ring, is pyramidal in shape with its apex upward and measures 2 inches in length, 1 1/4 in width and 3/4inch in thickness. These measurements are greatly altered by pathologic conditions. The lobe is related medially to the thyroid and the cricoid cartilages, the cricothyroid and the inferior constrictor muscles, the trachea, the esophagus and the external and the recurrent laryngeal nerves. Some describe the medial surface as being related to 2 tubes (esophagus and trachea), 2 nerves (recurrent and external laryngeal) and 2 muscles (inferior constrictor and cricothyroid).The lobe is related posteriorly to the common carotid and the inferior thyroid arteries and the longus cervicis muscle. Superficially, it is covered by the sternohyoid, the omo-
FIG. Embryology of the thyroid gland: (A) course of the thyroglossal duct, (B) lateral view of the thyroglossal duct and possible locations of accessory thyroid glands.
FIG. The thyroid gland. (A) The gland has been presented as a transparent structure to show the relations of the vessels and nerves. The path of the interior thyroid artery can be followed. (B) Cross section through the isthmus of the thyroid gland. (C) The thyroid gland viewed from the left side. The gland is in relation to 2 nerves (recurrent and external laryngeal), 2 tubes (esophagus and trachea) and 2 muscles (inferior constrictor and cricothyroid).
hyoid and the sternothyroid and is overlapped by the sternocleidomastoid muscle. The isthmus, which occasionally is absent, is a bar of thyroid tissue, varying in width and lying under cover of the skin and the fascia in the median line of the neck. It is situated on the 2nd, the 3rd and the 4th tracheal rings and is nearer the lower than the upper pole. A triangular projection, or pyramidal {middle) lobe, extends upward usually from the left side of the upper border of the isthmus and is connected to the hyoid bone by a fibromuscular slip called the levator glandulae thyroidae.
Arteries. The arteries of the thyroid gland are 2 pairs, the superior and the inferior thyroids, and sometimes a single artery, the thyroidea ima. The superior thyroid artery is the first branch of the external carotid; it supplies infrahyoid, laryngeal and sternocleidomastoid branches in the carotid triangle. It passes down under cover of the “strap” muscles and at the superior pole of the thyroid gland trifurcates into an anterior branch that supplies the front of the gland, a posterior that goes behind and an isthmic (arcuate) branch that joins its fellow of the opposite side along the upper border of the isthmus. The superior laryngeal nerve is situated only a little higher than the superior thyroid artery and, if the vessel is grasped too high, the nerve may be included in the ligature. The inferior thyroid artery is a branch of the thyrocervical trunk which arises from the first part of the subclavian. Although the superior vessel enters the superior pole, the inferior thyroid does not enter at the inferior pole of the gland. It travels upward along the medial border of the scalenus anterior muscle as far as the level of the 6th cervical vertebra and turns medially behind the vagus nerve and the common carotid artery. It passes in front of the vertebral vessels and, continuing downward, reaches the posterior border of the gland to which it is finally distributed. To do this it makes a hairpin turn, the summit of which varies considerably as to its level. It also supplies the larynx, the pharynx, the trachea, the esophagus and the surrounding muscles. As the artery reaches the thyroid it is crossed either in front or behind by the recurrent laryngeal nerve. A large branch of the vessel ascends along the posterior border of the gland to anastomose with a descending branch from the superior thyroid artery. The thyroidea ima is a branch from the innominate or the aortic arch. It varies in size from a tiny arteriole to a vessel as large as the inferior thyroid, which it may replace. It passes upward over the anterior surface of the trachea, under cover of the thymus, and reaches the inferior border of the isthmus. Its presence should be kept in mind when performing a low tracheostomy and during thyroid surgery. The accessory thyroid arteries are small vessels supplying the esophagus, the trachea and the thyroid gland. The 4 major thyroid arteries may be ligated, but the blood supply to the gland remains surprisingly good because of these accessory vessels.
Veins. The veins of the thyroid form a rich plexus situated in front of the gland. As they leave the gland, they form 3 main trunks in the form of superior, middle and nferior thyroid veins. The superior thyroid vein is the only venous trunk that accompanies the artery of the same name. It leaves the upper part of the gland, taking as its guide the outer border of the omohyoid muscle, crosses the common carotid artery and ends in the internal jugular vein. The middle thyroid vein has no accompanying artery. It leaves the gland about its midportion, follows the inner border of the omohyoid, crosses the common carotid artery and ends in the internal jugular vein. The inferior thyroid veins commence at the lower pole of the gland and at the lower border of the isthmus; they pass downward in front of the trachea and may be connected by several transverse branches and end in the left innominate vein. Nerves. Two nerves are related to the thyroid gland: the superior and the recurrent (inferior) laryngeal. Both are branches of the vagus nerve. The superior laryngeal nerve arises from the inferior ganglion (nodosum), passes downward and medially and crosses behind the internal carotid artery. It divides into the internal and the external laryngeal nerves. The internal laryngeal nerve, the larger of the two branches, is accompanied by the superior laryngeal branch of the superior thyroid artery and with it pierces the thyrohyoid membrane at the posterior border of the thyrohyoid muscle. It is purely sensory and supplies fibers to the floor of the piriform fossa and the mucous membrane of the larynx above the vocal cord. The external laryngeal nerve accompanies the superior thyroid artery but is placed on a deeper plane. It passes deeply to the upper pole of the thyroid gland and is distributed to the cricothyroid and the inferior constrictor muscles. During ligation of the superior thyroid vessels, the external laryngeal nerve (nerve to the cricothyroid) is in danger. It may be included in the ligature, and such inclusion would cause a weakness or huskiness of the voice. However, this condition is temporary and becomes normal within a few months. The recurrent {inferior) laryngeal nerve is a structure of vital importance in thyroid surgery. Considerable variations in its position may take place so that the nerve may penetrate and traverse the gland proper, may be behind the gland, or may remain in the tracheo-esophageal groove. During thyroid surgery, when the gland is dislocated forward and medially, the nerve usually hugs the side of the trachea. Then it is located not in the tracheo-esophageal groove but on the posterolateral aspect of the trachea. It always passes posterior to the joint that exists between the inferior cornu
FIG. The nerve supply of the thyroid gland: (A) the thyroid isthmus has been cut to show the course of the recurrent laryngeal nerve; (B) the nerves are shown on the left, and the arteries on the right.
FIG. 144. Possible locations of the recurrent laryngeal nerve: (A) behind the inferior thyroid artery; (B) in front of the inferior thyroid artery; (C) high origin, this accounts for the inability to find the nerve during thyroidectomy; (D) origin around the inferior thyroid artery; (E) extralaryngeal division. In some instances the nerve may pass between the branches of the artery.
of the thyroid and the cricoid. This cartilaginous prominence formed by the joint is a valuable guide to the nerve. On the right side the recurrent leaves the vagus nerve as it crosses the first part of the subclavian artery, turns upward and medially behind that artery and the common carotid and travels in the groove between the trachea and the esophagus. It ascends in this groove to the lobe of the thyroid gland and crosses or is crossed by the inferior thyroid artery. Upon reaching the lower border of the inferior constrictor muscle it passes deeply to it so as to gain access to the muscles of the larynx. It supplies the muscles that act on the vocal folds but also supplies sensory branches to the mucous membrane of the larynx below these folds. Therefore, it is both sensory and motor. On the left side, the nerve arises within the thorax after turning around the arch of the aorta and then ascends in the neck in the tracheo-esophageal groove. To aid in the exposure of the recurrent laryngeal nerve, M. M. Simon has constructed an anatomic triangle which can be identified readily. It is bounded by the recurrent laryngeal nerve anteriorly, the common carotid artery posteriorly, and the inferior thyroid artery forms its base. The triangle is dependent on the variations and the anomalies that may take place. The recurrent laryngeal nerve supplies all the intrinsic muscles of the larynx with the exception of the cricothyroid. There is a voluminous and confusing literature concerning the innervation of the larynx. Some of this confusion resulted from the difficulty of interpreting the various positions of a paralyzed vocal cord. To add to the confusion, a completely paralyzed or cadaveric cord may resume normal function, and a presumably incompletely paralyzed vocal cord would remain unchanged in a position of adduction with good tension for decades. The variety of responses and positions has been clarified and explained by the works of King and Gregg, who directed attention to the anatomic reasons for these various positions. They state that some recurrent laryngeal nerves divide into two trunks extralaryngeally, thus supplying fibers to the abductor and the adductor muscles, respectively. On the basis of these findings one can assume that if a paralyzed vocal cord is observed in the midline with good tension, the recurrent nerve is divided extralaryngeally, and the posterior division, which supplied the abductor muscle, has been injured. The abductor group of muscles, thus being unopposed, have pulled the vocal cord to the midline. In such a patient there would be no dyspnea, and the speaking voice would be normal. If a vocal cord is completely paralyzed (cadaveric) and is in an inter-
FIG. Simon’s triangle. This aids in the identification of the recurrent laryngeal nerve. It is bounded anteriorly by the recurrent nerve, posteriorly by the common carotid artery, and the inferior thyroid artery forms its base. The inferior horn of the thyroid cartilage also makes an excellent guide to the nerve.
FIG. Transverse sections through the larynx (vocal cord level): (A) normal glottic space; (B) early bilateral abductor paralysis, the patient can breathe but the voice is impaired; (C) late bilateral abductor paralysis, voice improves but dyspnea and inspiratory laryngeal stridor appear; (D) anatomic relations.
FIG.(Facing page). Subtotal thyroidectomy.
(A) The incision is placed in a transverse skin crease. (B) The investing layer of deep cervical fascia is opened along the anterior border of the sternocleidomastoid muscle. (C) Division of the sternohyoid and the omohyoid muscles on the right. The same is done on the left side. These muscles should be severed high so that their nerve supply (ansa hypoglossi) is not injured. (D) The sternohyoid and the omohyoid muscles have been dissected upward and downward. The sternothyroidon the right side has been severed. (E) Isolation and division of the middle thyroid vein; this permits entrance into the posterior thyroid space. (F) Ligation of the superior thyroid vessels.
FIGURE (Caption on facing page.)
FIGURE (Caption on facing page.) . Subtotal thyroidectomy (Continued). (G) Identification of the recurrent laryngeal nerve and ligation of the inferior thyroid artery. (H) Ring of forceps placed into the right lobe. Each hemostat bites into thyroid tissue proper and in this way protects the recurrent laryngeal nerve and the parathyroid glands. (1) Removal of the right lobe, the isthmus and the pyramidal lobe. (J) Protective ring of forceps in place; each hemostat is replaced by a ligature. (K) Approximation of the thyroid remnant. (L) Closure.
mediate position between abduction and adduction, then it must be assumed that theentire Jaryngeal nerve has been injured. In such a patient there would be marked hoarseness and an absence of dyspnea. The effects of such an injury could be compensated if the opposite normal cord is capable of crossing the midline. Therefore, it is important to notice on examination of the larynx whether or not a vocal cord fails to move and also to determine its position and tension. If both recurrent nerves are cut (bilateral abductor paralysis) the vocal cords become lax and cannot be tensed. This results in immediate impairment of voice but rarely causes difficulty in breathing. It is interesting to note that within 3 to 5 months the voice begins to return. This is due to a fibrosis and shrinking of the vocal cords which were previously lax. A few weeks later, the fibrotic process results in fixation of the vocal cords as they approach each other. The fibrotic contraction causes the cords to approach the midline, narrowing the glottic space to a thin slit. As a result of this, dyspnea begins to make its appearance, especially on exertion, resulting in a marked limitation of physical effort. The sympathetic nerve supply to the thyroid gland is derived from the sympathetic ganglia. The fibers from the middle and the inferior cervical ganglia reach the gland as nervous networks along the superior and the inferior thyroid arteries.
Lymph Drainage. The thyroid gland is drained by 2 sets of lymph vessels, the ascending and the descending, each consisting of medial and lateral groups. The medial group of the ascending vessels leaves the upper border of the isthmus and passes to the lymph glands situated on the cricothyroid membrane; they are known as the prelaryngeal glands. The lateral ascending vessels leave the upper part of the gland and accompany the superior thyroid artery to the deep cervical chain that is situated at the bifurcation of the common carotid. The medial descending vessels pass to the glands on the trachea, the pretracheal glands. The lateral descending vessels pass from the deep surface of the thyroid to small glands placed about the recurrent laryngeal nerve.
SURGICAL CONSIDERATIONS
LIGATIONS OF THYROID VESSELS
Ligation of the
Ligation of the Inferior Thyroid Artery. The most common approach is along the medial border of the sternocleidomastoid, but it has been approached along the lateral border. For the mesial approach, an incision is made along the anterior border of the sternocleidomastoid muscle. Transverse incisions produce less scarring. The incision is made through the superficial layer of deep cervical fascia, and the sternocleidomastoid muscle is retracted laterally. Dissection is continued in the interval between the carotid sheath and the thyroid gland. The middle thyroid vein is severed before the proper cleavage plane is found, and the recurrent laryngeal nerve must be avoided. Isolation and ligation of this vessel as it is done in routine thyroidectomies is described in detail elsewhere.
THYROIDECTOMY
Subtotal Thyroidectomy. This operation is performed frequently, and since technical errors might result in disaster, any anatomic points that make for a safer operation should be stressed. The incision should be so placed that the average string of beads will cover the scar. No fixed point can be mentioned, since necks vary in their length, but generally these incisions should be 1 or 2 fingerbreadths above the sternal notch and extending from one sternocleidomastoid to the other. This is deepened until the subplatysmal cleavage plane is reached. Having found this avascular plan, the upper flap, consisting of skin, subcutaneous fat and platysma, is grasped and dissected upward, well above the level of the notch of the thyroid cartilage. This exposes the superficial layer of deep cervical fascia and the anterior jugular veins. The anterior borders of the sternocleidomastoid muscles are now identified; the investing layer of deep cervical fascia is incised here. In this way the prethyroid muscles are separated from the sternocleidomastoid which is mobilized. The latter is retracted outward, and adequate exposure of the prethyroid muscles is obtained. A vertical incision is made in the midline between the two prethyroid muscle bundles and is extended from the thyroid notch to the level of the sternal notch. The sternohyoid and the omohyoid are clamped and divided high, thus protecting their nerve supply. It is an error to state that the prethyroid muscles have been severed, since the underlying sternothyroid usually remains intact after this step. A distinct cleavage plane exists between the sternohyoid and the sternothyroid. The sternohyoid and the omohyoid, having been incised, are dissected both upward and downward. The sternothyroid muscle is severed transversely, exposing the thyroid gland. The last maneuver opens the so-called “surgical capsule”. The gland is grasped by forceps, rotated medially, and the internal jugular vein in the carotid sheath is retracted laterally. This maneuver places the thin pretracheal fascia, on the stretch, where it attaches to the thyroid gland, and in this tissue the middle thyroid vein is sought. It is severed and ligated, and the posterior thyroid space is entered (Fig. 148 E). This permits medial dislocation of the gland. With medial traction on the thyroid, and lateral traction on the carotid sheath, dissection takes place in the proper cleavage plane. The upper pole is identified, as is the entrance of the superior thyroid vessels. These are doubly ligated, off the pole, and severed. Careful separation of the pretracheal layer of pretracheal fascia will reveal the recurrent laryngeal nerve and the inferior thyroid artery. If deemed necessary, the artery is ligated. A ring of forceps is placed around the right thyroid lobe which includes the isthmus; each forceps grasps thyroid tissue proper. The lobe, the isthmus, and the pyramidal lobe are removed above this protective ring. The clamped thyroid tissue is ligated, and the thyroid that remains is approximated to itself or sutured to the pretracheal fascia. The left lobe is removed in similar fashion. The severed muscles are resutured; and the skin, the superficial fascia and the platysma are approximated as one layer.
Total thyroidectomy is usually done for carcinoma of the thyroid. On the involved side the sternocleidomastoid muscle, the internal jugular vein, the thyroid vessels and all demonstrable lymphatics are included in the dissection and are removed en bloc. Included in this dissection are the prethyroid muscles.
Thyroglossal Duct. This duct originates at
FIG. Removal of a thyroglossal duct: (A) course of a patent thyroglossal duct and cyst; (B) incision; (C) dissection to the hyoid bone; (D) cutting the hyoid bone; (E) an assistant’s finger placed in the mouth and pressing on the tongue makes the deeper part of the duct more accessible; (F) dissection completed.
an early stage in fetal life as a depression in the midline of the posterior third of the tongue which is known as the foramen caecum. From it a solid cord of cells grows downward which becomes canalized to form the duct that passes downward in the midline of the neck between the genioglossi muscles. It extends as far as the upper border of the thyroid cartilage and then turns to either side of the midline. This part of its course is represented after birth by the pyramidal lobe of the thyroid gland and a musculofibrous band connecting that lobe to the hyoid bone. Frazer seems to have settled the question as to whether the duct runs in front of, behind or through the hyoid bone. His works demonstrate that the duct passes in front of the body of the hyoid and then curves up behind the bone before again continuing downward. Therefore, it is important to remove this section of the hyoid bone when removing a patent duct. After passing the thyroid cartilage, the thyroglossal duct expands to form the thyroid gland. If the duct remains patent, a thyroglossal cyst develops. Such a cyst is found usually above the thyroid cartilage and in the midline. Hamilton Bailey has stated that if these cysts develop below the thyroid cartilage, they naturally follow the course of the duct and appear to one or the other side of the midline, usually to the left. Normally, the
thyroglossal duct does not open onto the surface of the skin of the neck. Therefore, a congenital thyroglossal fistula is not possible, and if a fistula does develop it must be secondary and brought about by a bursting of or an opening into a thyroglossal cyst. Since the thyroid gland develops from the thyroglossal duct, an accessory or misplaced thyroid may develop anywhere along the line of the duct. The lingual thyroids are sometimes found at the back of the tongue in the region of the foramen caecum. The term “ectopic thyroid” means thyroid tissue found in an incorrect position, thus differing from the accessory thyroid. If a thyroglossal duct swelling appears above the hyoid bone, it is necessary only to split the mylohyoid muscle along its raphe, separate the geniohyoid muscle and remove the tumors. However, if these cysts or tumors appear subhyoid, the dissection must be more radical and include removal of a portion of the hyoid bone. Thyroglossal cysts, fistulae and sinuses must be removed radically to accomplish a cure. The cyst is exposed by a transverse incision that is carried down to the sternohyoid muscles. These are divided vertically in the midline, and the cyst is dissected free to the level of the hyoid bone. To expose the sinus completely, a small portion of hyoid bone must be removed in the midline. An assistant’s finger placed in the patient’s mouth and passed over the back of the tongue enables him to push the foramen caecum and any remaining portion of the sinus tract within reach of the operator. Since the duct is small and cannot be seen clearly, it is best to dissect some of the surrounding tissue with it. Therefore, in the removal it is necessary to include some small portion of the mylohyoid, the geniohyoid and the genioglossus muscles. Deep structures are sutured; divided edges of the hyoid bone are approximated; the wound is closed with or without drainage. PARATHYROID GLANDS
The parathyroid glands are yellowish-brown bodies, the number and the position of which are variable. A superior and an inferior parathyroid are usually present on each side, occupying any position from the back of the pharynx to the superior mediastinum. They are about the size of a small pea and usually lie between the posterior aspect of the lateral lobe of the thyroid and the pretracheal lamina of pretracheal fascia. The parathyroids lie entirely or partially within the substance of the thyroid gland, this being particularly true of the superior, which are then easily removed in thyroidectomy. The anatomy of the inferior parathyroids is more complex than that of the superior, and the inferior lie in intimate relationship to the inferior thyroid arteries and veins. Their position is variable. Walton has described three rather typical positions of the parathyroids in relation to their surrounding fascial plane: (1) the gland lies below the inferior thyroid artery and is then anterior to the pretracheal fascia; (2) the gland lies above the artery and is then frequently situated deep to the pretracheal fascia and visible only upon incising the fascia; (3) the parathyroids may be in the substance of the thyroid gland proper. If a tumor develops in a parathyroid in the first-described position, it may pass between the two capsules of the thyroid, along the inferior thyroid veins, in front of the common carotid artery and finally come to lie behind the sternum. If such a tumor is situated behind the pretracheal fascia, it cannot be seen until the fascia is incised and an inspection made even around the circumference of the esophagus. It may even pass into the thorax behind the esophagus. The superior and the inferior parathyroid glands receive their blood supply from the corresponding thyroid vessels.
THYMUS GLAND
Embryologically, the thymus appears as 2 entodermal diverticula which arise one on either side of the 3rd branchial pouch. A ventral diverticulum of the 4th pouch may take part in the formation of the gland or entirely disappear. As the 2 diverticula grow they meet and become joined by connective tissue, but there is never any real fusion of thymus tissue proper. Actually, therefore, there are 2 asymmetric thymus glands a right and a left which are easily separated by blunt dissection.
The adult thymus gland is a temporary organ that is “sandwiched” between the sternum and the great vessels in the region of the superior mediastinum. It is essentially an organ of the growing period of life which undergoes gradual atrophy after puberty. From birth to puberty it grows relatively slowly; there are tremendous individual variations at any given age. At birth it ranges in weight from 2 to 17 Gm., the average being 13 Gm.; at puberty its average weight is about 37 Gm., but cases have been reported in which it has scarcely been recognizable at this age. In the young adult the average weight is usually reduced to about 25 Gm. The thymus gland is located partly in the neck and partly in the mediastinum, and it is roughly pyramidal in shape with its apex directed upward; in the infant this apex may be in actual contact with the thy-
FIG. The thymus gland: (A) enlarged thymus gland extending in front of the pericardium; (B) development of the thymus.
roid gland. It is soft in consistency, and its shape varies with its size and the age of the individual. In infants with short thoraces it is broad and squat, but in adults with long thoraces it is drawn out into 2 irregular flattened bands. It is of pinkish-gray color and has a lobulated surface.Anteriorly, the thymus gland is related to the sternum and the lower end of the sternothyroid muscles. In the young child, its lateral margins may be insinuated between the pleura and the upper costal cartilages. Posteriorly, it is related from below upward to the pericardium, the ascending aorta,
FIG. The cervical part of the esophagus begins opposite the inferior margin of the cricoid cartilage at the level of the body of the 6th cervic al vertebra. (Inset) Cross section at the level of the first thoracic vertebra. The trachea does not cover the esophagus completely but leaves a part of its left anterior margin exposed; this makes surgical access easier from this side.
the left innominate vein, the trachea and the inferior thyroid veins. It is surrounded by a fibrous capsule that separates it from these structures. It is connected to the thyroid by a strand of tissue called the thyrothymic ligament. The arterial supply of the thymus is received through inconstant branches derived chiefly from the internal mammary artery or its branches. Veins. These vessels are irregular and drain mainly into the internal mammary or the left innominate. Lymphatics. The gland has a profuse lymphatic drainage, and certain of the lymphatics open directly into veins without first traversing lymph glands. Occasionally, the thymus retains its infantile size in the adult and for some unknown reason does not atrophy. In such cases there is a large quantity of lymphoid tissue throughout the body, and the condition is then known as status lymphaticus.
CERVICAL PORTION OF THE ESOPHAGUS
The entire esophagus is about 10 inches long and extends from the end of the pharynx through the lower part of the neck and through the superior and the posterior mediastinum. It pierces the diaphragm and enters the stomach opposite the 9th thoracic spine about 1 inch to the left of the midline. The cervical esophagus is a direct continuation of the pharynx. It commences opposite the inferior margin of thg cricoid cartilage at the level of the body of the 6th cervical vertebra. An excellent landmark which locates this point is the carotid tubercle. The trachea does not cover the esophagus completely but leaves a portion of its left anterior margin exposed, making surgical access easier on this side. As the esophagus descends from the level of the 6th cervical vertebra, it lies in front of the vertebral column and overlaps both longus cervicis (colli) muscles. At the inlet of the thorax the left common carotid is anterior to its left border; the thoracic duct, the left subclavian artery and the pleura are situated on its left side. Higher up the common carotid is also on its left side, and both are overlapped by the thyroid gland. At times the posterior part of the lateral thyroid lobe may enlarge and insinuate itself upon the anterior surface of the esophagus causing difficulty in swallowing. The esophagus and the pharynx are loosely attached to the prevertebral fascia and in this way form the retropharyngeal and the retro-esophageal spaces. Abscesses in these spaces are hindered from extending laterally and thus take the path of least resistance, which is downward the mediastinum. Because of its loose connection with the prevertebral fascia and because of its elasticity, this portion of the esophagus can be displaced upward and laterally for a considerable distance. When the esophagus is empty, it is flattened anteroposteriorly, and its lumen appears only as a slit, but when distended it becomes irregularly cylindrical and presents its typical constriction points, the first and narrowest of which is at its commencement.
SURGICAL CONSIDERATIONS
ESOPHAGEAL DlVERTICULUM Shallow and Lahey have done extensive work in this field, and the former has reported a series of cases in which 1-stage diverticulectomy has been accomplished with excellent results. A longitudinal incision is made along the anterior border of the sternocleidomastoid muscle and is carried through the skin, the superficial fascia and the superficial layer of deep cervical fascia. The sternocleidomastoid is retracted backward until the omohyoid muscle is demonstrated; this is severed at the point where it disappears beneath the sternocleidomastoid. With the omohyoid retracted, the thyroid gland is separated from the internal jugular vein and the common carotid artery. Then the thyroid gland is pulled toward the midline, and the inferior thyroid artery is exposed. This often crosses over the diverticulum or gets in the way of its dissection; hence, it is best to ligate and sever it. Since a diverticulum is a herniation of mucous membrane through muscle fibers, it should be remembered that there are two weak points in the musculature of the posterior aspect of the pharynx and the esoph-
FIG. Esophageal diverticulectomy (one stage). (A) A longitudinal incision is made along the anterior border of the sternocleidomastoid muscle. (B) The omohyoid muscle is severed, and the thyroid gland is retracted medially: the sternocleidomastoid muscle and the carotid sheath are retracted laterally. The inferior thyroid artery is exposed, ligated and severed as it crosses the diverticulum. (C) Fibers of the inferior constrictor muscle are severed, and the sac is mobilized. (D) The sac is ligated close to the pharynx. (E) Closure is effected m layers.
agus; these two points are at the level of the lower fibers of the inferior constrictor, and where the cricopharyngeal muscle diverges from the lowest fibers of the inferior constrictor. These are the two locations where diverticula are most commonly found; however, the approach is usually through the left side of the neck because the esophagus passes to the left of the vertebral bodies. Shallow has made successful use of the esophagoscope to isolate and aid in the dissection of the diverticulum which is closely bound to the longitudinally running esophagus by the enveloping fibers of the cricopharyngeal muscles. These are separated at the lowest angle of the sac, the fundus is grasped with blunt forceps, and traction is made. The remaining fibers of the cricopharyngei enveloping the diverticulum are cut. When the neck of the sac is reached, the fibers of the inferior constrictor are seen along the lower border of the neck; these must be severed to mobilize it completely. The neck of the sac is transfixed and ligated, and the sac is removed. This ligation should take
FIG. The submaxillary (digastric) triangle. (A) The superficial layer of deep cervical fascia has been removed, exposing the floor and the contents of the triangle. The submaxillary gland, which overflows the triangle, also has been removed. (B) Coronal section, showing the superficial layer of deep cervical fascia investing the submaxillary gland.
place close to the pharynx. The cricopharyngeus and the inferior constrictor should be closed over the ligated and invaginated sac to prevent a recurrence of the hernia. SUBMAXILLARY (DIGASTRIC) TRIANGLE
The submaxillary, or digastric, triangle is bounded by the anterior and the posterior bellies of the digastric and the inferior border of the mandible. The roof is fascial, being formed by the investing (superficial) layer of deep cervical fascia as it passes between the mandible and the hyoid bone. Three muscles make up the floor: the mylohyoid, the hyoglossus and the middle constrictor muscle of the pharynx. These
FIG. The floor of the submaxillary triangle: (A) the floor is trimuscular and is formed by the mylohyoid, the hyoglossus and the middle constrictor muscles; (B) the middleconstrictor muscle, seen from within; (C) the hyoglossus muscle.
muscles constitute important surgical landmarks and can be identified by the direction of their fibers and the fact that they lie on successively deeper planes. The fibers of the mylohyoid muscle arise from the mylohyoid line of the mandible, run downward and medially and insert into a median raphe which extends from the chin to the hyoid bone. With its fellow of the opposite side it forms a diaphragm oris. The free oblique posterior fibers reach the hyoid bone and overlap the hyoglossus muscle, whose fibers arise from the hyoid, pass directly upward to the lateral surface of the tongue where they attach and interdigitate with the styloglossus. The posterior fibers form a free margin which overlaps the middle constrictor muscle of the pharynx. The fibers of the latter originate from the cornu of the hyoid bone and are directed horizontally and backward to the median raphe.During dissection of this triangle, the following structures are encountered: the skin, the superficial fascia, the platysma and the cervical branch of the facial nerve, which passes down behind the angle of the mandible and lies between the platysma and the deep cervical fascia. Incisions made behind the angle of the jaw may injure this nerve and, since it supplies the quadratus labii inferioris, a drop in the angle of the mouth may result. This usually disappears within 3 months.
FIG.The pharynx, viewed from behind; with 3 constrictor muscles intact.
The anterior facial vein crosses the triangle superficially and at the lower margin of the mandible accompanies the external maxillary artery. The deep cervical fascia (investing layer) envelops or invests the submaxillary salivary gland which overflows the triangle and conceals the trimuscular floor and the digastric muscle. The gland is separated posteriorly from theparotid by the stylomandibular ligament, which is the thickened part of the parotid fascia between the styloid and the angle of the mandible. The submaxillary gland is indented by the posterior free edge of the mylohyoid muscle and in this way is divided into a superficial and a deep (oral) part. Its duct (Wharton’s) leaves its deep surface, passes forward deeply to the sublingual gland and opens into the floor of the mouth on the sublingual papilla at the side of the frenulum linguae. When the submaxillary gland is freed and retracted upward the mylohyoid nerve is visible; it is accompanied by the submental branch of the facial artery. If the free posterior border of the mylohyoid muscle is identified, the lingual and the hypoglossal nerves are seen passing behind this border. These nerves are separated by the oral part of the submaxillary gland and its forwardrunning Wharton’s duct. The lingual nerve, Wharton’s duct and the hypoglossal nerve run behind the mylohyoid muscle and on the hyoglossus muscle. The hypoglossal nerve is
FIG. The pharynx viewed from behind, with the 3 constrictor muscles removed.
usually accompanied by 1 or 2 veins. These relationships may be seen when the superficial part of the submaxiUary gland is cut away and the mylohyoid muscle is detached at the hyoid bone and median raphe. If the hyoglossus muscle is cut parallel with and above the hyoid bone the lingual artery is exposed, lying deep to the hyoglossus muscle while the vein accompanying the hypoglossal nerve lies on this muscle. The vein should not be confused with the artery. An additional vein usually accompanies the lingual artery.
PHARYNX
The pharynx is a large vestibule that is common to the respiratory and the digestive tracts. It is a vertically placed musculomembranous tube that extends from the base of the skull to the cricoid cartilage where it becomes continuous with the esophagus. The 6th cervical vertebra marks its lower border posteriorly. It is about 5 inches long and has a transverse diameter greater than the anteroposterior. The widest part ( 1and 3/4 inches) is opposite the hyoid bone, and the narrowest (3/4 inch) is at the esophageal orifice. Since it communicates with the nose, the mouth and the larynx, it has been divided into 3 parts: nasopharynx, oropharynx and laryngopharynx.
Nasopharynx (Epipharynx). This is somewhat cube-shaped and is placed behind the cavity of the nose, above and behind the soft palate. It is part of the respiratory and not of the digestive tract. Its walls, with the exception of the soft palate, are incapable of movement; therefore, the cavity remains patent, and its form never changes. Its anterior wall is formed by the posterior apertures of the nose (choanae) through which it opens into the nasal cavities. These apertures are a pair of oblong openings that slope from the base of the skull downward and forward to the posterior border of the hard palate and are separated by the vomer. By looking through them with a postnasal mirror a view is obtained of the posterior end of the inferior and the middle conchae and the 2 lower meatuses. Each opening is about 1 inch long and 1/2 inch wide. The roof and the posterior wall are considered together as an obliquely sloped surface formed by the body of the sphenoid, the basilar process of the occipital bone and a thick layer of ligamentous fibrous tissue which fills in the angle between the latter and the vertebrae. The roof and the posterior wall are supported by the inferior surface of the body of the sphenoid, the basilar part of the occipital bone and the anterior arch of the atlas below. The posterior wall, especially in childhood, presents a mass of lymphoid tissue known as pharyngeal tonsils (adenoids) which may fill the nasopharynx and hinder or completely block nasal breathing. The floor is made up of the soft palate and the uvula and is the only movable boundary of the nasopharynx. It prevents food from being regurgitated into the nose. Behind the soft palate the nasopharynx is continuous with the oral pharynx through the isthmus. The lateral wall presents the opening of the pharyngotympanic tube (eustachian) which is on a level with and about Yi inch behind the inferior nasal concha. The entire side wall measures a little over 1 inch in diameter. The posterior boundary of the eustachian opening presents a prominent elevation (eustachian cushion) which is derived from the cartilaginous portion of the tube, behind which lies the pharyngeal recess (Rosenmuller’s fossa). A fold of mucous membrane, the salpingopharyngeal fold, descends from the posterior lip of the orifice and contains the salpingopharyngeus muscle, which gradually disappears as it passes downward. When adenoids occlude the orifice of the tube, the air in the tympanic cavity gradually becomes absorbed, and deafness may result. The tympanum can be inflated through the pharyngeal orifice of the tube by means of a eustachian catheter. The instrument is passed backward along the floor of the inferior meatus until it reaches the posterior wall of the nasopharynx. If the catheter is rotated laterally through a right angle, its point rises in the pharyngeal recess. Then it may be withdrawn from the nose until the point catches the tubal projection. When a mirror is introduced through the mouth so that the nasopharynx is illuminated by reflected light,
FIG. 159. Sagittal view of the pharynx. The 3 parts of the pharynx have been subdivided.
a view is obtained of the 4 orifices that open into the nasal part of the pharynx; the middle and the superior meatuses of the nose, and the middle and the superior conchae can be brought into view and their pathology determined. The side walls and the orifices of the pharyngotympanic tubes also can be fully inspected.
Oropharynx (Mesopharynx). This is partly respiratory and partly alimentary. It is the posterior continuation of the mouth cavity that lies behind the mouth and the tongue.
The anterior wall presents the opening into the mouth, the lower portion being the pharyngeal part of the dorsum of the tongue that faces directly backward. The epiglottis, which belongs to the laryngeal part of the pharynx and is situated immediately behind the tongue, appears as a leaflike plate of cartilage enveloped in mucous membrane with its upper part standing prominently up and behind the tongue. The posterior wall is smooth and is supported y the body of the axis, which is separated from the pharynx by the prevertebral fascia.The lateral wall is formed by the interval between the palatoglossal and the palatopharyngeal arches that is occupied by the tonsils. A retropharyngeal abscess produces a swelling of the posterior pharyngeal wall that may bulge forward and obstruct the air passages during respiration.
Laryngopharynx (Hypopharynx). This is the longest of the 3 subdivisions; it lies behind the larynx and diminishes in width
FIG. The muscular coat of the pharynx (side view). The origin of the 3 constrictor muscles is along a continuous line from above downward.
from above downward. Its upper part is common to the digestive and the respiratory tracts, but its lower part, opposite thecricoid, is entirely digestive. Its anterior and posterior walls are in contact except when food is swallowed. The anterior wall is formed by the inlet of the larynx and the posterior aspect of the arytenoid and the cricoid cartilages. The posterior wall is in contact with the anterior and is supported by the bodies of the 3rd, the 4th, the 5th and the 6th cervical vertebrae. The lateral walls are supported by the posterior part of the lamina of the thyroid cartilage and present a small fossa, the piriform recess, which is bounded on its medial side by the aryepiglottic fold. The mucous membrane of this area is supplied by the internal laryngeal nerve; hence, if a crumb or a small particle of food lodges in the fossa, uncontrollable coughing results. Pharyngeal Wall. This wall presents 4 rather distinct layers: buccopharyngeal fascia, muscular, fibrous and mucous coats.
1. The buccopharyngeal fascia is a layer of fibrous tissue covering both the buccinator and the pharyngeal muscles. It also invests the constrictor muscles of the pharynx, and between it and the prevertebral fascia a loose areolar tissue is found which forms an easily distensible space in which pus may spread. This layer contains the venous plexus, which drains the pharynx and communicates with the pterygoid plexus. It enters the jugular veiear the angle of the jaw.
2. The muscle coat of the pharyngeal wall is made up of 5 paired voluntary muscles: the 3 constrictors (superior, middle and inferior) which constitute an outer circular layer, and the stylopharyngeus and the palatopharyngeus which constitute an inner longitudinal layer. The 3 constrictor muscles are incomplete
in front, but each widens posteriorly and joins its fellow in the median plane at the median raphe. Each muscle is somewhat fanshaped and is attached by its front end or handle to the side wall of the nasal, the oral or the laryngeal cavity. Each partly overlaps externally the muscle above it, so that the inferior overlaps the middle, and the middle overlaps the superior. The origin of these muscles is continuous from above down. The superior constrictor originates from the lower third of the posterior border of the medial pterygoid plate, the pterygomandibular ligament, the side of the tongue, the mucous
FIG. The larynx; 4 views and a disarticulated larynx are shown.
membrane of the mouth and the mylohyoid line. The middle constrictor originates from the stylohyoid ligament and the hyoid bone. The inferior constrictor arises from the oblique line of the thyroid cartilage and the fascia covering the cricothyroid muscle. They are inserted into a median raphe situated posteriorly, and all are supplied by the pharyngeal plexus through the accessory part of the spinal accessory nerve. The inferior constrictor receives 2 additional nerves: the external and the recurrent laryngeal branches of the vagus. The stylopharyngeus muscle enters the wall of the pharynx between the superior and the middle constrictors. Itmeets the palatopharyngeus muscle and is inserted with it into the posterior border of the thyroid cartilage. This is visible only after cutting the inferior constrictor muscle. The stylopharyngeus is supplied by the glossopharyngeal nerve, and the palatopharyngeus by the accessory nerve.
3. The fibrous coat has been called the pharyngobasilar fascia, the pharyngeal aponeurosis and also the submucous coat. It is strong in its upper part and takes the place of muscle tissue where the superior constrictor is absent. As it passes downward it gradually becomes weaker until it is finally lost as a distinct layer. It forms the principal attachment between the pharynx and the base of the skull.
4. The mucous coat consists of a columnar, ciliated epithelium in the nasopharynxand stratified squamous in the lower part. The various structures pass in a definite arrangement between the constrictor muscles. Between the base of the skull and thesuperior constrictor are the tensor palati, the pharyngotympanic tube and the levator palati. Between the superior and the middleconstrictors are the stylopharyngeus muscle and the glossopharyngeal nerve. Between the middle and the inferior constrictors are the internal laryngeal nerve and the superior laryngeal artery. Between the inferior constrictor and the esophagus are the recurrent laryngeal nerve and the inferior laryngeal artery.
LARYNX
This upper and specialized portion of the windpipe extends from the epiglottis to the cricoid; it forms the organof the voice. At birth it lies opposite the 3rd and the 4th cervical vertebrae but gradually descends until in the adult, it lies opposite the 3rd, the 4th, the 5th and the 6th cervical vertebrae. It is situated in thefront and upper part of the neck, below the tongue and the hyoid bone, and between the great vessels of the neck. Above, it opens into the pharynx and below into the trachea. In the midline, it is covered by skin and cervical fascia but laterally is overlaid by the sternohyoid, the sternothyroid, the thyrohyoid and the origin of the inferior constrictor muscles. It consists of cartilages, ligaments and muscles and is lined by mucous membrane. Laterally, it is embraced by the lateral lobes of the thyroid gland, above which it is related to the carotid sheaths. Behind, it rests upon the pharynx which separates it from the body of the 3rd to the 6th cervical vertebrae. After puberty, the larynx is smaller in the female than in the male, the vocal cords in the former being about two thirds the length of the latter.
Cartilages of the Larynx. These are 9 iumber: the epiglottis, the thyroid, the cricoid, 2 arytenoids, 2 corniculates and 2 cuneiforms. The epiglottis is a leaf-shaped lamina of yellow fibrocartilage covering the superior aperture of the larynx. It guards the entrance to the larynx and is situated behind the median thyrohyoid ligament, the hyoid bone and the back of the tongue. Its pointed lower end is attached firmly by the thyroepiglottic ligament to the posterior surface of the fused alae of the thyroid cartilage just below the thyroid notch. Its expanded upper end projects upward beyond the hyoid bone and presents a free border covered by mucous membrane both anteriorly and posteriorly. The anterior surface is connected to the dorsum of the tongue by a median glossoepiglottic and by right and left pharyngoepiglottic folds. The corresponding depression on each side of the median plane forms the vallecula. The floor of the vallecula lies immediately above and behind the hyoid bone. The posterior surface of the epiglottis lies in the anterior wall of the vestibule of the larynx. The thyroid cartilage is the largest of the laryngeal cartilages, and its name is derived from the Greek which means “like a shield.” It is formed by a pair of broad quadrilateral laminae that are fused together in front but are widely separated behind. The fusion of these 2 laminae anteriorly in the midline of the neck has a more marked angulation in males and is known as the “pomum Adami” (laryngeal prominence or Adam’s apple). The anterior borders of these laminae are united only in their lower halves, the upper halves being separated by a V-shaped thyroid notch. The laryngeal prominence and the thyroid notch can be felt easily subcutaneously and thus serve as valuable landmarks. The free and rounded posterior border projects upward as a superior horn and downward as an inferior horn. The superior horn is attached to the tip of the greater cornu of the hyoid bone by a lateral thickened border of the thyrohyoid membrane called the lateral thyrohyoid ligament. The inferior horn articulates at its extremity with the side of the cricoid cartilage. An important oblique line begins on the lateral surface of the cartilage in front of the root of the superior horn, extends downward and forward and ends behind the middle of the inferior border. This line gives insertion to the sternothyroid muscle and origin to the thyrohyoid muscle.The area in front of it is covered by the thyrohyoid, and the narrower posterior area gives origin to a part of the inferior constrictor muscle of the pharynx. The inferior border of this cartilage is in relation to the circumference of the cricoid cartilage to which it is attached by the cricothyroid membrane. As life progresses this cartilage begins to ossify and may become fractured. The cncoid cartilage is shaped like a signet ring with the wide part posterior. It is a palpable landmark that indicates the beginning of the trachea and the level of the superior border of the esophagus. Its narrow anterior part, which is palpable through the skin, is called the arch and lies on a level with the 6th cervical vertebra. The posterior part, the lamina, is much deeper, projects upward and occupies the lower part of the gap between the 2 laminae of the thyroid cartilage. The arch is attached to the thyroid cartilage by the cricothyroid membrane and below is fixed to the first tracheal ring by an elastic membrane known as the cricotracheal ligament. The two arytenoid cartilages appear as triangular pyramids, whose apices are directed upward and whose bases articulate with the upper aspect of the posterior portion of the cricoid. They help fill the gap between the 2 laminae of the thyroid cartilage. The posterolateral angle of the base is called the muscular process because it provides attachment to the cricoarytenoid muscles. The anterior angle of the base is prolonged forward as a spinelike process called the vocal process because the true vocal cords attach here. The 2 corniculate cartilages have been referred to as the cartilages of Santorini. They are small and conical and are attached to the apex of each arytenoid cartilage. They give attachment to the aryepiglottic folds. The 2 cuneiform cartilages have been referred to as the cartilages of Wrisberg. They are a pair of little rod-shaped cartilages that are placed in the aryepiglottic folds in front of the corniculate cartilages. Membranes of the Larynx. The membranes that make up the chief connecting bands of the larynx are the thyrohyoid and the cricothyroid. The thyrohyoid membrane connects the upper border of the thyroid cartilage to the upper part of the posterior surface of the hyoid bone, in this way suspending the larynx from the hyoid. The median portion of thismembrane is thickened and is called the median thyrohyoid ligament; its cordlike right and left margins are referred to as the lateral thyrohyoid ligaments. The median thyrohyoid membrane is pierced by the internal laryngeal nerve and the superior laryngeal vessels on each side. The lateral thyrohyoid ligament passes from the superior horn of the thyroid to the tip of the greater cornu of the hyoid bone, where a small cartilaginous nodule, the cartilago triticea, is found. The cricothyroid membrane occupies the interval between the cricoid and the thyroid cartilages and consists of a central and 2 lateral portions. The central portion connects the cricoid and the thyroid cartilages and presents a hole in the midline through which the cricothyroid artery sends a branch. This vessel is used as a landmark in laryngeal surgery. The lateral part of the membrane (conus elasticus) is attached below to the upper border of the cricoid cartilage but is free above except at its extremities. It is fixed in front in the angle between the thyroid laminae and behind to the vocal processes of the arytenoids. The free border of the cricothyroid membrane which results is covered by mucous membrane and forms the true vocal cord. The ventricular band that is covered by mucous membrane and forms the false vocal cord extends from the angle between the thyroid laminae to the anterolateral surface of the arytenoids. These lie above the true vocal cords.
Muscles. The muscles of the larynx are extrinsic and intrinsic. The extrinsic muscles have been described elsewhere; they act upon the voice box as a whole. They are the omohyoid, the sternohyoid, the sternothyroid, the thyrohyoid and certain suprahyoid muscles (stylopharyngeus, palatopharyngeus, inferior and middle constrictors of the pharynx). The intrinsic muscles, on the other hand, confine themselves entirely to the larynx and act on its parts to modify the size of the laryngeal aperture (rima glottidis) and also control the degree of tension of the vocal ligaments. The principal intrinsic laryngeal muscles are the cricothyroid, the arytenoids (transverse and oblique), the posterior cricoarytenoids, the lateral cricoarytenoid and the thyroarytenoid. All of these, with the exception of the transverse arytenoid, are in pairs.
The cricothyroid muscle is the only intrinsic muscle that lies on the exterior of the larynx. It arises from the lateral surface of
FIG. The intrinsic muscles of the larynx; 4 views are shown
the cricoid, runs upward and backward and is inserted into the inferior horn of the thyroid cartilage. It bridges the lateral portion of the cricothyroid interval. The cricothyroid muscles are the chief tensors of the vocal ligaments; this action is accomplished by pulling the arch of the cricoid upward around its articulation with the inferior horn of the thyroid cartilage, thus forcing the arytenoids backward and stretching the vocal cords. The posterior cricoarytenoid is probably the most important of the laryngeal muscles,since its action separates (abducts) the vocal cords, thus widening the rima glottidis. All the other muscles close the larynx by a more or less sphincteric (adduction) action. The cricoarytenoid arises from the back of the cricoid, runs upward and outward to the muscular process of the arytenoid where it inserts. By pulling backward on this process the vocal cords are separated. Bilateral abductor paralysis of these muscles results in suffocation. When both recurrent laryngeal nerves are injured, bilateral abductor paralysis results, and the vocal cords become lax and cannot be abducted. At first this rarely results in dyspnea, but the loss of
FIG. The action of the intrinsic muscles of the larynx. (A) The action of the posterior cricoarytenoid muscles, separating the vocal cords. (B) By the contraction of the cricothyroid muscle, the vocal ligaments are tensed. (C) Adduction of the vocal cords is brought about by the contraction of the oblique and transverse arytenoids muscles.
voice is immediate. Within 3 to 5 months the voice begins to improve but, unfortunately, dyspnea also makes its appearance. This is the result of atrophy and fibrosis. Within a few weeks the voice becomes more improved, but as the vocal cords continue to fibrose and gradually approach each other the dyspnea becomes severe, especially on exertion. The laryngoscope will reveal the presence of a mere slit. The transverse arytenoid is the only unpaired muscle of the larynx. It is a thin, flat, muscular band passing from the back of one arytenoid cartilage to the other. When it contracts, it draws the posterior parts of the arytenoids together, helping to close the laryngeal inlet during swallowing. The oblique arytenoid muscles are a pair of weak muscular slips that lie on the back of the transverse muscle and cross each other, forming a letter X. This muscle continues on as the aryepiglotticus in the aryepiglottic fold in which it reaches the epiglottis. Its action draws the arytenoids together and shortens the aryepiglottic fold. This approximates the arytenoids and the epiglottis. The muscle acts as a sphincter for the laryngeal inlet during swallowing. The lateral cricoarytenoid muscle arises from the upper aspect of the lateral part of the cricoid, runs upward and backward and is inserted into the muscular process of the arytenoid. These muscles are adductors of the vocal cords and reduce the width of the rima glottidis. The thyroarytenoid is an upward continuation of the lateral cricoarytenoid. It arises from the deep surface of the thyroid lamina, passes backward and inserts into the anterolateral surface of the arytenoid cartilage. It pulls the arytenoid cartilage forward and slackens the vocal folds. The uppermost fibers of this muscle curve upward into the aryepiglottic fold, are called the thyroepiglottic muscles and join with the aryepiglottic muscles to insert in the edge of the epiglottis. Some of the deepest fibers of the thyroarytenoid form a muscle bundle, the vocal muscle; this cannot be separated from the rest of the muscle and actually is the inner constant part that lies in the vocal lip lateral to the vocal ligament. It draws the vocal process forward, relaxing the vocal ligaments. The action of the laryngeal muscles is threefold: (1) they open the glottis and permit breathing; (2) they close the glottis and the vestibule during swallowing; (3) they regulate the tension of the vocal cords. The first two actions are automatic and are controlled by the medulla, but the third is voluntary and is controlled by the cerebral cortex. The posterior cricoarytenoids are the only abductors. The lateral cricoarytenoids adduct the cords. The muscles that close the vestibule are the thyroarytenoid, the aryepiglottic and the thyroepiglottic. The muscles that effect the tension of the cords are the cricothyroid, the vocalis and the thyroarytenoid.
Nerves of the Larynx. The nerve supply is derived from the vagus nerve by way of its 2 branches, the superior and the inferior (recurrent) laryngeal, both of which are mixed nerves. After a short course, the superior laryngealnerve divides into a thin external and a stouter internal branch. The external laryngeal nerve is applied to the inferior constrictor muscle and passes deeply to the insertion of the sternothyroid. In its course it passes to and is accompanied by the superior thyroid artery; it sends a few twigs to the inferior constrictor, pierces it and ends by supplying the cricothyroid muscle. The internal laryngeal nerve is sensory and pierces the thyrohyoid membrane as several diverging branches. It crosses the anterior wall of the piriform recess and supplies sensory fibers to the larynx above the vocal cords. Nordland and other investigators believe that this nerve innervates the interarytenoid muscle in most cases. Division of the superior laryngeal nerves results in a loss of sensation to the laryngeal mucous membrane, making it difficult or impossible for the patient to perceive a foreign body in the larynx. There is also a weakening or paralysis of the cricothyroid, which produces a huskiness of the voice. The inferior (recurrent) laryngeal nerve arises at different levels on the 2 sides. On the right it arises in the root of the neck and winds around the subclavian artery, but on the left it arises in the superior mediastinum and winds around the arch of the aorta. It ascends anterior to the tracheo-esophageal groove and can be felt on the lateral aspect of the trachea. It continues upward and becomes intralaryngeal by passing deep to the lower border of the inferior constrictor muscle. The point at which this nerve becomes intralaryngeal is on a level with the inferior horn of the thyroid cartilage.
Vascular Supply of the Larynx. This is derived from the superior laryngeal branch of the superior thyroid artery and the inferior laryngeal branch of the inferior thyroid artery.
Lymphatics. The lymphatics from the upper part end in glands in the carotid triangle, and from the lower part in the glands in front of and besides the larynx and the trachea.
Cavity of the Larynx. This may be divided into 3 compartments: vestibule (supraglottic), middle compartment (glottic area) and an infraglottic area. Some authors have likened the superior aperture of the larynx to a triangle, the base of which is at the
FIG. The inlet of the larynx as seen through a laryngeal mirror. The inset shows the structures magnified and identified.
epiglottis, the sides formed by the arytenoepiglottic folds, and the apex located at the arytenoid commissure posteriorly.
Inlet of the Larynx. The inlet, or upper aperture, faces almost directly backward so that it is set at right angles to the long axis of the laryngeal tube. It is bounded above by the free margin of the epiglottis, on either side by the aryepiglottic folds of mucous membrane which stretch from the epiglottis to the arytenoid cartilage, and below by the short interarytenoid fold of mucous membrane. Two small elevations are notedat the posterior extremity of the aryepiglottic fold. The most anterior protrudes to a higher plane and is the cuneiform cartilage (Wrisberg). The posterior, which is set on a slightly lower plane, is produced by the corniculate cartilage (Santorini), which is situated on the apex of the arytenoid cartilage. These 2 small elevations are easily visible on laryngoscopic examination. The anterior wall of the vestibule is longer than the posterior and is formed throughout by mucous membrane
FIG. Thyrotomy, laryngotomy and tracheotomy incisions.
which covers the posterior aspect of the epiglottis. Its central point is marked by a rounded elevation, the tubercle of the epiglottis, which is important because it is the most noticeable feature on laryngoscopic examination and is frequently the only structurethat is visible in the hands of a novice. The aryepiglottic folds contain the aryepiglottic muscles between its two layers of mucous membrane. Posteriorly, the vestibule is bounded by the arytenoid cartilages and the interarytenoid fold containing the transverse arytenoid muscle. The aryepiglottic and transverse arytenoid muscles are of great importancebecause they close the inlet of the larynx during the act of swallowing. The vestibular fold of mucous membrane passes backward and laterally from the thyroid angle. It contains a small fibrous band, the vestibular ligament (false vocal cord), which stretches from the thyroid angle to the arytenoids cartilage. This fold narrows the lower end of the vestibule.
Glottis. The glottis, or middle compartment, is the narrowest part of the interior of the larynx; it measures nearly 1 inch anteroposteriorly in the adult male and about 3/4 inch in the female. It consists of a small sinus, the ventricle or recess, and is situated between the vestibular and the vocal folds. The arytenoid cartilages are posterior and are separated by the interarytenoid notch. Approximately two thirds of the anterior part of the glottis consists of the true vocal cords, the posterior third consisting of the interval between the arytenoid cartilages. The mucosa uniting the 2 arytenoid cartilages forms the posterior or arytenoid commissure and is the usual site of tuberculosis of the larynx.
Vocal Cords. The true vocal cords diverge as they pass posteriorly and extend from the vocal process of the arytenoid to the thyroid angle. They appear as short straight folds that are characterized by the pallor of the covering mucous membrane. This pallor is produced by the absence of loose submucous tissue as well as the absence of blood vessels. The rima glottidis {glottic slit) is that fissure which separates the true vocal cords and the arytenoid cartilages; it is triangular when at rest, linear during phonation and lozenge-shaped in respiration. The glottis is closed after inspiration, thus aiding fixation of the diaphragm during efforts of expulsion (parturition, defecation, urination and vomiting) .The infraglottic, or lowest compartment of the larynx, extends from the true vocal cords to the first tracheal ring. Its walls are made up of the thyroid and the cricoid cartilages and the cricothyroid membrane. In emergency laryngotomy this membrane is incised to gain entrance into the larynx. SURGICAL CONSIDERATIONS
Thyrotomy (Laryngofissure). The incision extends from the hyoid bone above to the cricoid cartilage below; it is placed exactly in the midline and deepened until the isthmus of the thyroid gland is exposed. If necessary, this is divided. When the thyroid cartilage is visualized, a vertical incision is made in the midline through it and the thyrohyoid membrane. Through this incision tumors of the larynx can be removed and treated when removal of the entire larynx is unnecessary. At times this operation also has been used for the removal of foreign bodies that could not be dislodged by other means. The two segments of thyroid cartilage and membranes are sutured together. Some authorities permit the divided cartilage to fall together without suturing.
Laryngotomy has been used as an emergency procedure when the presence of a foreign body or edema necessitates the rapid admission of air into the larynx. It has also been used as a preliminary step in extensive operative procedures. A cyanosed and almost asphyxiated patient can be relieved immediately by this operation, in which a transverse incision is made across the midline of the neck at the level of the upper border of the cricoid cartilage. If the incision is kept close to the upper border, the cricothyroid artery will be avoided. Then it is deepened to and through the cricothyroid membrane, and a laryngotomy tube is inserted. It should be remembered that the cricothyroid space, in children, is so small that it is usually unsuitable for this operation. In extreme emergencies where death from asphyxia appears imminent, the blade of a pocket knife has been successfully plunged directly through the cricothyroid membrane and the opening kept patent by rotating the handle of the knife.
Tracheotomy (tracheostomy) may be an elective or emergency procedure. If elective, it is usually a preliminary step to laryngectomy for malignant disease. However, if it is done as an emergency operation it is utilized where there has been sudden obstruction of the airway as a result of aspiration of a foreign body, edema of the larynx, infections and edema about the throat, or postoperative vocal cord paralysis following injury to both recurrent nerves. Distinction has been made between low and high tracheotomy, the low being below the isthmus of the thyroid and the high above it. Most authorities are of the opinion that the low operation is preferable. Here an
FIG. Tracheostomy
.
incsion is made extending from the lower border of the thyroid cartilage downward for about 3 inches in the midline of the neck. The skin and the subcutaneous tissues are divided, and the anterior jugular vein is either ligatcd or retracted. The sternohyoid muscles are separated in the midline and retracted laterally, exposing the isthmus of the thyroid gland. This in turn is either cut between hemostats or retracted upward, since a low tracheotomy is desirable. At this stage a sharp hook is usually placed beneath the cricoid cartilage in the midline to steady the trachea and pull it forward. Usually the 3rd, the 4th and the 5th tracheal rings are divided from above downward, the opening held open and a tracheotomy tube inserted.
POSTERIOR (lateral) TRIANGLE
The posterior triangle of the neck is formed as a result of a longitudinal cleavage of what, in embryonic life, was a single muscle plate. This single muscle later becomes the sternocleidomastoid and the trapezius which have a continuous attachment above, extending from the inion to the tip of the mastoid. The attachment is aponeurotic and produces the roughened superior nuchal line. Below, and because of the cleavage, the attachments become disconnected so that the trapezius attaches to the lateral third of the clavicle and the sternocleidomastoid to the medial third. The posterior triangle is bounded by the posterior border of the sternocleidomastoid muscle, below by the middle third of the clavicle and behind by the anterior border of the trapezius; the apex of the triangle is the meeting point of the trapezius and the sternocleidomastoid, and when anterior and posterior borders fail to meet on this line, the area is occupied by part of the splenius capitis muscle. The inferior belly of the omohyoid muscle crosses the lower part of the posterior triangle, separating it into an upper, larger occipital triangle and a lower, smaller supraclavicular one. The roof of the posterior triangle is made up of the investing layer of the deep cervical fascia. The floor is muscular and is formed by the following three muscles from above downward: the splenius capitis, the levator scapulae and the scalenus medius. This muscular floor is carpeted by the prevertebral fascia.
Relations. The triangle is related to the following structures from superficial to deep: skin, superficial fascia, platysma, external jugular vein, posterior border of the sternocleidomastoid muscle, four cutaneous nerves that pierce the investing fascia, the spinal accessory nerve, the posterior belly of the omohyoid muscle, the transverse cervical artery and vein, the transverse scapular artery and vein, the prevertebral fascia, the muscular floor and the nerves that lie upon it.
Skin. The skin of the posterior triangle of the neck is thicker over the upper and posterior part of the triangle than over the lower and anterior part. The superficial jascia is usually thin; fat in this region tends to accumulate under the deep fascia rather than superficially.
Platysma Muscle. This muscle lies in the superficial fascia of the side of the neck. It arises from the deep fascia covering the pectoralis major and the deltoid muscles as low as the 2nd rib. Its fibers pass upward and medially and become inserted into the lower border of the mandible. Some of the upper fibers reach the face, decussate and mingle with the muscles of the lower lip. It can be seen from its course that the platysma leaves the middle line of the neck and the lower part of the anterior triangle uncovered. The nerve supply of the platysma is by way of the cervical branch of the facial nerve. If a skin incision is made along the sternocleidomastoid muscle and the skin and the superficial fascia are reflected carefully either backward or forward, the platysma appears as a very delicate sheet. There is a definite cleavage plane below it, which is filled by loose areolar tissue and in which the external jugular vein is found.
The external jugular vein travels subplatysmally. It varies greatly in size and is formed by the union of the posterior auricular with a branch of the posterior facial vein. It begins in or at the lower part of the parotid gland, passes vertically downward and across the sternocleidomastoid muscle. In the angle between the clavicle and the posterior border of the sternocleidomastoid it pierces the deep fascia and joins the subclavian vein. It receives the following branches: posterior jugular, anterior jugular, oblique jugular, transverse scapular and transverse cervical.
The posterior border of the sternocleidomastoid muscle should be noted because of the nerves in relation to it. Four superficial nerves pierce the investing layer of deep cervical fascia which is not a strong layer and at times is difficult todisplay. They can be remembered easily if the landmarks are named from above downward: occiput, ear, neck and clavicle. Thus, there are the lesser occipital, the greater auricular, the anterior cutaneous and the supraclavicular nerves. They all appear from approximately the same point, namely, the posterior border of the middle of the sternocleidomastoid muscle. The lesser occipital nerve passes upward and along the posterior border of the sternocleidomastoid muscle to reach and supply the skin of the lateral part of the occipital region. The greater auricular nerve runs parallel with the external jugular vein and supplies the skin that covers the angle of the jaw, the parotid gland, the ear and the skin over the mastoid region. The anterior cutaneous nerve of the neck appears close to the great auricular nerve and runs transversely forward across the sternocleidomastoid muscle; it divides into ascending and descending branches and supplies most of the skin of the side and the front of the neck. In its course across the sternocleidomastoid it lies either superficially or deeply to the external jugular vein. The supraclavicular nerves arise a little below the preceding nerve as a single trunk that divides into 3 branches: lateral, intermediate and medial supraclavicular nerves which diverge from one another. The medial branch descends over the medial third of the clavicle and supplies the skin of the front of the chest down to the level of the sternal angle. The intermediate crosses the clavicle and descends on the thoracic wall as far as the 2nd rib. The lateral branch passes over the trapezius muscle and the acromion and innervates the skin on the upper and back parts of the shoulder region. The spinal accessory nerve is the highest and most important structure in the triangle. It is placed very superficially, lying immediately beneath the investing layer of fascia. It appears at about the middle of the posterior border of the sternocleidomastoid muscle, running under this muscle. Here some small lymph glands surround it, and the lesser occipital nerve takes a recurrent course below it. Branches from the 3rd and the 4-th cervical nerves run parallel with the accessory and may be mistaken for it. These cervical nerves also sink into the trapezius muscle and aid in its innervation. The fact that the accessory nerve is the highest structure in the triangle should avoid confusion.The inferior (posterior) belly of the omohyoid muscle springs from the upper border of the scapula and the suprascapular ligament under cover of the trapezius muscle. It is located about 1 inch above the clavicle, passes upward and enters the posterior triangle at its lower and posterior angle. As it continues forward and slightly upward, it crosses the brachial plexus, continues to the sternocleidomastoid muscle, crosses the scalenus anticus and joins the tendon that connects it to the superior belly of the muscle. The tendon lies under cover of the sternocleidomastoid and on the internal jugular vein. The inferior belly, as it crosses theposterior triangle, lies superficial to the suprascapular nerve, the transverse cervical
artery and the brachial plexus. The muscle can be felt through the skin and the fascia a little above the clavicle. Its movements may be seen in a thin person while he is talking. It lies between the investing and the prevertebral layers of the deep cervical fascia and is covered by a specially thickened part of the pretracheal layer. This thickened fascia binds the muscle to the posterior surface of the clavicle and to the 1st rib. In order to dislocate the inferior belly, its fascia should be incised along its upper border and the muscle pulled downward. The nerve supply to the omohyoid is through the ansa hypoglossi. The transverse cervical artery lies under the omohyoid muscle. It is a branch of the thyrocervical trunk, and as it passes backward it crosses the scalenus anticus and the phrenic nerve. In its course it
FIG. The posterior triangle. (A) The floor is trimuscular, being made up of the splenius capitis, the levator scapulae and the scalenus medius. The prevertebral fascia forms a carpet for this floor; the fascia has been incised and retracted in this figure. Four nerves pierce the investing fascia, and 4 nerves lie deep to it. (B) Cross section; the fascia is represented in blue.
FIG. Variations of the subclavian vessels in the region of the scalenus anterior muscle. E. B. Kaplan has described some of these variations herein depicted. The so-callednormal arrangement is noted in the center of the illustration: (A) double subclavian vein arrangement; (B) the formation of a venous ring; (C) the formation of an arterial ring; (D) both the artery and vein pass in front of the muscle; (E) a reversed arrangement inwhich the vein is behind the muscle and the artery in front of it; (F) both the artery and the vein pass behind the muscle.
also crosses the brachial plexus and the suprascapular nerve. In the occipital triangle it divides into a superficial and a deep branch, the superficial supplying the deep surface of the trapezius muscle, and the deep branch accompanying the levator scapulae muscle to the scapula and taking part in the scapular anastomosis. Occasionally, the transverse cervical artery is small and spends itself in the trapezius; it then is referred to as the superficial cervical artery. The transverse scapular or suprascapular artery is also found in the lowermost portion of the supraclavicular triangle, and it too is a branch of the thyrocervical trunk. It runs laterally and downward under cover of the sternocleidomastoid, across the scalenus anticus muscle and the phrenic nerve. It passes laterally behind the middle third of the clavicle and in front of the subclavian artery toward the posterior angle of the triangle. From this point on it accompanies the suprascapularnerve to the scapular. Behind the clavicle it is closely accompanied by one or two veins. The suprascapular and the transverse cervical veins run quite superficial to their arteries. Therefore, the arteries are accompanied not by their own veins but by slender venules as they cross the scalenus anticus muscle. The veins end in the external jugular. The suprascapular and the transverse cervical arteries clamp the phrenic nerve onto the scalenus anticus muscle. The prevertebral fascia forms a carpet that covers the cervical part of the brachial plexus and the subclavian vessels and provides a fascial sheath for them as they enter the axilla. The carpet also covers 4 motor nerves: those to the levator scapulae, the rhomboids, the serratus anterior and the diaphragm. Since the spinal accessory is the highest nerve in the posterior triangle, one may dissect cephalad to it without much risk, since the only other structure in the region of the apex of the posterior triangle is the artery. The floor of the triangle is muscular. The levator scapulae muscle occupies the most central position of the 3 muscles named. It arises from the posterior tubercles of the transverse processes of the upper 4 cervical vertebrae and is inserted into the vertebral border of the scapula between the root of the spine and the superior angle. Cephalad to the levator and parallel with it is the\splenius capitis muscle which arises from the lower half of the ligamentum nuchae and the succeeding vertebral spines. It passes upward and laterally, forming the upper part of the floor, and is inserted into the mastoid process and the adjoining part of the occipital bone, under cover of the sternocleidomastoid muscle. Caudad to the levator scapulae and parallel with it are the 3 scalenus muscles. The scalenus medius arises from the posterior tubercles of all the cervical transverse processes (2nd, 3rd, 4th, 5th and 6th) and is inserted into the upper part of the 1st rib between the groove for the subclavian artery and the neck of the rib. It is best not to consider the scalenus posterior as a separate muscle but as that portion of the scalenus medius that passes on to the 2nd rib and inserts there. The scalenus anterior is separated from the medius and the posterior by the brachial plexus and the subclavian artery. It arises from the anterior tubercles of all the transverse processes (3rd, 4th, 5th and 6th). Its posterior border is parallel with and, therefore, hidden by the posterior border of the sternocleidomastoid muscle. It is not considered actually as part of the floor of the posterior triangle, since it is hidden from view. The scalenus anterior inserts into the scalene tubercle (Lisfranc), which is situated on the upper surface of the 1st rib. Of the structures that lie between the accessory nerve and the omohyoid, the largest and most outstanding is the brachial plexus. Its upper part lies in the occipital triangle, but most of the plexus, as it passes through the neck, lies behind the inferior belly of the omohyoid and in the supraclavicular triangle. The formation of this plexus has been discussed on page 635. When the posterior border of the sternocleidomastoid is drawn forward, the nerves forming the plexus are seen emerging from between the scalenus anterior and the medius. This relationship is a useful landmark as it enables these 2 muscles to be identified. The supraclavicular nerve is quite thick and runs downward and backward immediately above the plexus. The nerve to the rhomboids is found a little higher; it pierces the substance of the scalenus medius muscle, runs downward and disappears under cover of the levator scapulae muscle to which it usually gives a branch. Its terminal branches supply the rhomboid muscle. If the upper part of the brachial plexus is pulled forward, the nerve to the serratus anterior commonly called the long thoracic nerve is seen. It arises from the back of the brachial plexus and disappears under cover of it. The nerve to the subclavius can be identified here.
PRACTICAL AND SURGICAL ASPECTS
Cervical Rib and Scalenus Syndrome. Adson and Coffey believe that tenotomy of the scalenus anticus muscle is preferable to the more radical resection of the cervical rib. The typical syndrome may occur wheo cervical rib is present, and in the absence of such a rib, the condition is referred to as the scalenus anticus syndrome (Naffziger). Ochsner, Gage and DeBakey believe that the scalenus anticus syndrome is produced by spasms and contractions of the muscle. They have been able to relieve the symptoms temporarily by injecting the muscle with procaine. The symptoms of compression of the brachial plexus and the subclavian artery are usually pain, numbness, atrophy and circulatory changes (cyanosis, ulcers, gangrene). A cervical rib attached to the transverse process and the body of the 7th cervical vertebra may vary from a simple bony bulge to a full and well-developed rib. If such a projection is small, its outer extremity may be free and unattached, but if it is longer, it may be joined to the 1st thoracic rib by fibrous attachments. The operative procedure that has given most success for both cervical rib and scalenus anticus syndrome is executed through an anterior approach that has been described by Adson. An oblique incision is made about 5 cm. in length, extending upward and backward from the sternoclavicular articulation into the posterior triangle of the neck. The incision is deepened through the fat and the platysma; the tendon of the sternocleidomastoid muscle is exposed at its clavicular attachment and is divided between forceps, the muscular portion being reflected mesially. The tendon of the omohyoid is found and may be either retracted or severed. The scalenus anticus muscle is identified, as is the phrenic nerve which runs obliquely across it from lateral to medial; the nerve is retracted. The borders of the scalenus muscle are dissected free, and its tendinous and muscular fibers are divided close to its insertion. The subclavian artery should be lateral to the scalenus anticus and the pleura medial. As soon as the muscle has been divided, the subclavian artery can be dissected free and will drop forward. A cervical rib, if present, is examined, and if it is causing no pressure, further operative procedure is unnecessary. However, if the rib or its tendinous attachment to the first rib is producing posterior pressure on the brachial plexus, a portion of the rib and the tendon must be removed. Brachial Plexus Lesions. Brachial plexus lesions are divided into those lesions that involve the entire plexus or only the upper, middle or lower portions of the plexus. When the entire plexus is involved either from injury or pressure, the following features are noted: complete anesthesia of the lower part of the arm, the forearm and the hand; flaccid paralysis of the superior extremities with eventual wasting of the muscles. Erb-Duchenne {upper arm) paralysis is the commonest type of nerve injury, occurring at birth and involving the 5th and the 6th cervical nerves. Upper-arm palsy usually results during the course of a complicated delivery with marked downward traction, resulting in a widening of the angle between the head and the shoulder. The injury usually occurs where the 5th and the 6th cervical nerves join to form the upper trunk of the plexus; this is known at Erb’s point, which is the spot where 6 nerves meet: 5th cervical, 6th cervical root, anterior division of upper trunks, posterior division of upper trunks, suprascapular nerve and the nerve
to the subclavius. The hand hangs at the sid in internal rotation with the forearm pronated and the fingers and the wrist flexed. This is referred to by some as the “head-waiter’s tip hand.” External rotation and abduction are lost at the shoulder, as are flexion and supination of the forearm. Some authorities are of the opinion that when this lesion occurs later in life, there is some associated dulling of sensation over the lower part of the deltoid, the arm and the forearm. The clinical appearance is produced by a paralysis of the abductors and the lateral rotators of the shoulder (deltoid, supraspinatus and infraspinatus) plus a paralysis of the flexors of the elbow (biceps, brachialis and brachioradialis); a weakness of the adductors and the medial rotators of the shoulders (pectoralis major, teres major, latissimus dorsi, subscapularis) also results. The pronator teres, the supinator, the flexors of the wrist and the thenar muscles may be slightly involved. The middle-arm type lesion involves the 7th cervical nerve and produces a paralysis
FIG. Sectioning of the scalenus anticus muscle and the removal of a cervical rib: (A) incision; (B) exposure of the scalenus anticus muscle after cutting the clavicular attachment of the sternocleidomastoid muscle; (C) a cervical rib causing pressure on the brachial plexus; (D) removal of a cervical rib.
of the entire radial nerve except its branch placed over the head. The lesion involves the to the brachioradialis; there is also a paraly- 8th cervical and the 1st thoracic nerve. It sis of the coracobrachialis. results in a paralysis of the intrinsic muscles Klumpke (lower-arm) paralysis is usually of the hand and a paralysis of the flexors of the result of upward traction on the shoulder, the digits; a “claw” hand results. In addition It may also be found in injuries or during there is diminished sensation over the medial breech presentations when the arms are side of the arm, the forearm and the hand.
Root of the Neck
The region referred to as the root of the neck is really the thoracocervical region that forms a boundary between the neck and the thorax and is occupied by structures that enter or leave the thoracic cavity. The right common carotid and the subclavian arteries arise from the innominate immediately behind the right sternoclavicular joint which is made up of the sternal end of the first costal cartilage, the medial end of the clavicle and the clavicular notch of the manubrium sterni. The joint and the scalenus anteriormuscle are landmarks in this region. The left common carotid and the subclavian arteries arise directly from the aortic arch and after a course of about 1 inch pass into the neck behind the left sternoclavicular joint. On the right side the two infrahyoid muscles intervene between the arteries and the joint, but on the left side the left innominate vein intervenes. On both sides the common carotid is placed in front of the subclavian artery at the entrance to the neck and ends in the carotid triangle by dividing into the internal and the external carotids. It has no collateral branches. Subclavian Artery. This artery courses through the neck and describes a gentle curve with the convex portion in an upward direction. The scalenus anterior muscle crosses the artery, dividing the vessels into 3 parts: the prescalenus (a part before), retroscalenus (a part behind) and postscalenus (a part after). Therefore, the artery not only occupies the root of the neck but the superior mediastinum as well and becomes the axillary artery at the lateral border of the first rib. The prescalenus portion of the artery passes upward and laterally to the medial border of the scalenus anterior. Anteriorly, the following structures are encountered in a lateral direction: the common carotid artery, the ansa subclavia, the vagus nerve and the internal jugular vein, the latter being separated in part from the artery by the vertebral vein and on the left side by the phrenic nerve. Posteriorly, the artery is intimately related to the cervical dome of the pleura and the apex of the lung. The branches from this part of the vessel are the vertebral, the thyrocervical trunk and the internal mammary. Grant has described a “triangle of the vertebral artery” which has as its base the first part of the subclavian artery, its lateral side is the scalenus anterior, and its medial side the longus cervicis, the apex being made up of the anterior tubercle of the 6th cervical transverse process . Anatomically, the triangle is seen best when the common carotid artery and the internal jugular vein are divided low. The posterior wall of the triangle, from above downward, is made up of the transverse process of the 7th cervical vertebra, the anterior ramus of the 8th cervical nerve, the neck of the 1st rib, and the cervical pleura which rises to the neck of the 1st rib. The triangle contains the vertebral artery, the vertebral vein which descends in front of the artery and crosses the subclavian artery, the inferior thyroid artery and the ganglionated sympathetic trunk. The retroscalenus portion of the subclavian artery lies behind the scalenus anterior and its superimposed structures. Posteriorly, it is in contact with the cervical dome of the pleura and the apex of the lung. It is located in that triangular space that exists between the anterior and the middle scalene muscles, the base or floor of which corresponds to the 1st rib. Above and lateral to it are the trunks of the brachial plexus; to see these relationships and this part of the artery it is necessary to cut the anterior scalene muscle transversely. Because of the presence of the phrenic nerve, dissection of this muscle cannot be complete if the nerve is not protected properly. The costocervical trunk arises from the posterior aspect of this part of the subclavian artery, passes backward above the pleura to the neck of the 1st rib where it divides into the superior intercostal and the deep cervical arteries. The postscalene portion of the subclavian artery extends from the lateral border of the scalenus anterior to the outer border of the 1st rib. Aneurysm of the subclavian, as a rule, involves this portion and appears as a swelling in the posterior triangle of the neck just above the clavicle. Because of the close proximity of the subclavian vein, an edema of the upper extremity may result. Ligation of
FIG. The arteries in the root of the neck: (A) the subclavian artery is divided into 3 parts by the scalenus anticus muscle; (B) the subclavian artery and vein are separated by the scalenus anticus muscle (side view).
this artery should be carried out in its third part. Subclavian Vein. This vein has only two parts that correspond to the second and the third parts of the artery; the beginning of the innominate vein substitutes for the first part. This is understandable if it is remembered that the internal jugular vein crosses the first part of the subclavian artery in order to make that union known as the innominate vein. The termination of the internal jugular then crosses and conceals the prescalenus portion of the subclavian artery; hence, no similar part of the subclavian vein exists; the subclavian is a continuation of the axillary vein. At the junction of the sternum with the clavicle the subclavian vein unites with the internal jugular to form the innominate. It begins at the outer border of the 1st rib, runs medially and almost transversely behind the clavicle, lying in front of the subclavian artery which it accompanies throughout its course with the exception of that point where the artery and the vein are separated by the anterior scalene muscle. The vertebral and the internal mammary veins pass directly intoit, there being no thyrocervical or costocervical venous trunks. The inferior thyroid veins drain into the innominate vein; the transverse cervical and suprascapular veins open into the external jugular vein. The deep cervical, the ascending cervical and the vein from the
FIG. The vertebral triangle and its contents.
first intercostal space drain into the vertebral before it crosses the subclavian artery to end in the innominate vein. The variations of the subclavian vessels have been described on page. The right innominate vein lies deeply to the inner end of the right clavicle from which it is separated by the sternohyoid and the sternothyroid muscles. It is related to the medial surface of the right pleura and partly overlies the innominate artery. It passes vertically downward into the superior vena cava. The left innominate vein passes downward behind the upper part of the manubrium to the lower margin of the first right costal cartilage where it ends in the superior vena cava. It is covered in front by the left sternoclavicular joint and on the right is overlapped by the right pleura. Remnants of the thymus intervene between it and the sternum. The vein is on the level of or at times slightly above the upper margin of the manubrium and is endangered in removal of tumors at the root of the neck or in low tracheotomy. Scalenovertebral Angle. This angle takes the form of an inverted V, is bounded laterally by the scalenus anterior muscle and medially by the longus cervicis (colli) muscle. These two muscles meet at the carotid tubercle (Chassaignac’s), which is the well developed anterior tubercle of the transverse process of the 6th cervical vertebra and forms the apex of the triangle.
The roof is formed by the sternocleidomastoid muscle. The lower part of this angle is crossed by the subclavian artery, which disappears behind the scalenus anterior muscle but, before disappearing, it gives rise to two large branches from its upper border: the vertebral artery and the thyrocervical trunk. As these two vessels ascend they fill the gap in the scalenovertebral angle. Vertebral Artery. This is the first and largest branch of the subclavian. It is divided into 4 parts: the first part passes upward and backward between the scalenus anterior and the longus cervicis muscles and through the foramen in the transverse process of the 6th cervical vertebra; it is surrounded by a plexus of sympathetic nerve fibers and is covered by the vertebral and the internal jugular veins. The second part ascends through the foramina in the transverse processes of the upper 6 cervical vertebrae. The third part emerges from the foramen transversarium of the atlas and passes almost horizontally backward and medially behind the lateral mass of the atlas.The fourth part pierces the spinal dura mater and travels upward into the cranial cavity through the foramen magnum, joining the internal carotid artery to form the circle of Willis. The vertebral vein descends in front ofthe artery and may hide it. As it descends, it deviates to the lateral side of the artery and crosses in front of the first part of the subclavian artery; it ends in the posterior aspect of the innominate veiear its origin. The thyrocervical trunk also arises from the upper part of the subclavian artery at the medial border of the scalenus anterior muscle and at once breaks up into 3 branches: the suprascapular, the transverse cervical and the inferior thyroid arteries. Only the inferior thyroid occupies the scalenovertebral angle. It reaches the level of the 6th cervical transverse process, turns medially and downward and terminates at the posterior border of the lobe of the thyroid gland. The course of this vessel resembles an inverted U. As the artery curves medially it passes over the vertebral vessels and below the carotid system. The thoracic duct occupies the left side of the scalenovertebral angle. Its course is similar to that of the inferior thyroid artery, but it loops in the reverse direction and at a lower level than does the vessel. In the neck the duct forms an arch that reaches as high as the 7th cervical vertebra, arching behind the carotid system (internal jugular vein, vagus nerve and common carotid artery), and in front of the vertebral system (vertebral vessels). As it passes to the left it also crosses the scalenus anterior muscle and the phrenic nerve. Continuing its course, it crosses the transverse cervical and transverse scapular arteries and usually ends as a single vessel entering the junction of the subclavian and the left internal jugular veins. The duct sometimes divides, one vessel entering the vein on the right and the other entering on the left side.
RECOMMENDED LITERATURE:
1. Mark W. Wolcott. Ambulatory Surgery End The Basic Of Emergency Surgical Care.-Philadelphia:J.B.Lippincott Company,2001.-752p.
2. Michael F. Mulroy.Regional Anesthesia /The
3. Richard M. Stilman,M.D.,E.A.C.S. General Surgery /Review And Assessment/
4. Kent M. Van De Graff, Stuart Ira Fox, Karen M. Lafleur. Synopsis of Human Anatomy and Physiology /WCB McGraw-Hill/, 2004.-675p.
5. John J. Jacobs. Shearer’s Manual Of Human Dissection /McGraw-Hill Information Services Company, 1998.-300p.
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7. Philip Thorek. Anatomy In Surgery /J.B.Lippincott Company/,1996.-935p.
