1.
Clinical anatomy, physiology of the external ear
2.
Otologyc examination
3.
Clinical anatomy, physiology and examination of the vestibular system
The ear consists of
three parts—the external, the middle and the
internal
- External Ear
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Fig. i.
Anatomy of the External, Middle and Internal Ear (Semi-Schematic
View)
(1) Pinna; (2) external
auditory meatus; (3) tympanic membrane; (4) tympanic
cavity; (5) malleus; (6) incus;
(7) stapes; (8) Eustachian tube; (9) vestibule; (10)
semicircular canals;
(11) cochlea; (12) auditory
(acoustic) nerve
The shell-shaped pinna (Fig. 2) is composed of a skin-covered cartilaginous lamella whose posterior surface is evenly convex
and smooth, while its anterior surface is concave, with semilunar folds and hollows
between them. The skin on the anterior surface
of the pinna adheres directly to the perichondrium; on the posterior
surface, however, it may form folds owing to the
presence of a small layer of loose cellular
tissue. The free anteroexternal margin of the pinna is known as the helix; towards
the bottom the pinna gradually turns into the lobe devoid of cartilage and consisting of well-developed fat and cellular tissue with a small number of vessels and nerves. The small protuberance of cartilage projecting over the external auditory meatus is named the tragus. In
front of the helix and parallel to it is a ridge
known as the an thelix, with the antitragus
at its posterior end.
The external auditory meatus extends from the funnel-shaped hollow {cavum conchae)
on the outer surface of the pinna to the tympanic membrane or drum. It is a canal directed horizontally inwards and a little forward. Its average length from the tragus top to the drum
edge is 3.5 cm. The drum at the end of the canal
separates the external and the middle ears.
The outer third of the auditory canal consists of
cartilage and membranous tissue, and both inner
portions of bone.
The external auditory meatus is curved in the
horizontal and frontal planes. The
cartilaginous and bony ðîã- tions of the meatus
form an obtuse angle opening forward and downwards.
Therefore, when examining the drum, the pinna must be pulled backwards and
upwards, in order to straighten out the meatus. The oval lumen of the external auditory meatus has a longitudinal
diameter of 1 cm. Its width varies with age and in
different individuals. Its narrowest part is the
isthmus, where the cartilaginous and bony portions
form a junction and where foreign bodies are most
likely to lodge. The walls of the auditory meatus are
lined with skin which in the bony portion
gradually becomes thinner, loses its
subcutaneous tissue and accretes closely with the periosteum. The skin covering the cartilaginous portion abounds in hair, sebaceous glands and cerum-inous
glands which secrete the earwax, or cerumen. The skin of the bony portion has neither hair, nor glands. The external bony meatus has four walls: the superior
wall formed by the squamous
portion of the temporal bone, its internal part
bordering on the floor of the middle cranial fossa;
the posterior wall serving as the front wall of the mastoid process; the anterior and inferior walls whose inner parts are formed by the tympanic portion of the temporal bone. The external third of the anteroinferior
wall is made up of cartilage with two vertical fissures
through which an inflammatory process in the external
auditory meatus can spread to the connective tissue surrounding the parotid gland, and vice versa. The anterior wall adjoins the articular head of the mandible, which explains why it is painful to open the mouth and chew in cases of inflammation of the anterior wall of the external auditory meatus. Injury to the lower jaw, a fall, or an upward blow to the chin may cause a fracture in the anterior wall of the auditory meatus with the articular
head of the mandible pushed backwards and
upwards.
In the newborn, there is neither bony auditory meatus,
nor mastoid process, and in place of the former there is a bony ring or annulus, which is deficient in a small upper section, and is directly connected with the membra-nocartilaginous auditory meatus. The inner border of the annulus has a bony furrow (sulcus) into which
the tympanic membrane is inserted. In the bone-free upper part, the drum is directly attached to the lower edge of the squamosa, the so-called notch of Rivinus. By
the end of the third year the external auditory
meatus is fully developed.
The external ear is supplied with
blood by branches of the external carotid
artery. It is innervated, in addition to the trigeminal branches, by the auricular nerve (ramus auricularis n. vagi) ramified in the
posterior wall of the auditory meatus. Mechanical irritation of the latter
wall, as in wax removal, often causes reflex cough. The
lymph from the walls of the auditory meatus drains into the nearest lymph nodes located in front of the auricle, on the mastoid process, and under the
inferior wall of the auditory meatus. Inflammations
in the external auditory meatus are often accompanied
by swelling and pain in these lymph nodes.
Tympanic
Membrane
The tympanic membrane (Fig. 3, coloured Table I, Fig. 1) or drum is a thin semi-transparent elliptical disc situated between the external and middle ear. It is 9.5-10 mmX X 8.5-9 mm in size.
The greater part of the drum fitted into the bony
furrow of the tympanic ring is taut, and is called
the pars tensa; the other, smaller part of the drum
facing forward and upwards and directly attached to the incisure in the squamosa
known as the notch of Rivinus (incisura Rivini) is lax, and is called the pars flaccida or
Shrapnell's membrane. The drum consists of
three layers: an outer or epidermal layer continuous with that of the auditory meatus, a middle layer of
radiating and circular connective tissue fibres, and an inner layer of mucosa continuous with the
mucous membrane of the tympanic cavity. Shrapnell's membrane or pars flaccida consists only of two layers and lacks the middle stratum of fibrous tissue.
In early childhood, the drum is
comparatively thick owing to the presence of a loose submucous layer. It grows compact with time and in old age becomes quite thin.
The drum is placed obliquely and
not perpendicularly to the long axis of the auditory meatus, so that it faces forward, downwards and inwards. In the newborns
and breast-fed babies, the drum is
almost horizontal.
Examination of the drum through
the auditory meatus reveals a
funnel-shaped concavity in its centre with an eminence called the umbo in its deepest place. The handle of the malleus embedded in the fibrous layer
of the drum starts from the umbo and goes forward and upwards to end above in a tiny knob the size of a pin-head—the short process. The two folds stretching anteriorly and posteriorly from the short
process separate the upper lax membrana flaccida from the lower taut membrana tensa.
Middle
Ear
The middle ear comprises the
tympanic cavity, the mastoid process with its
cellular system and the Eustachian tube
(Fig. 4), all directly interconnected.
The tympanic cavity is a small chamber, about 1 cu cm !n size, lying in the depth of the temporal bone, between
the tympanic membrane and the internal ear. In
front, through the Eustachian
tube, the tympanic cavity communicates
with the nasopharynx; behind, through the entrance }nto the mastoid antrum (aditus ad antrum.
Fig. 4. Section Showing Middle
Ear 1) Eustachian tube;
(2) tympanic cavity; (3) antrum; (4) mastoid cells
The tympanic cavity, similar to the cells of the mastoid process, contains air
coming through the Eustachian tube.
It is customary to divide the
tympanic cavity into three parts: the middle and
biggest part, mesotympanum, corresponding to the pars tensa of the drum; the
upper part, epitympanum, lying above the former and also
known as the epitympanic
recess or attic; the lower part, hypotym-panum, lying below the drum level.
The tympanic cavity has six walls.
The roof of the tympanic
cavity is a thin plate of bone separating the
tympanic cavity from the middle cranial fossa where the temporal lobe is
situated. This plate often has congenital
fissures through which vessels pass from the middle cranial fossa. These anatomical
features may account for the meningeal symptoms frequently observed in young children with acute otitis media.
The inferior wall or floor of
the tympanic cavity is separated from the
jugular bulb by a fairly thick bony plate. Bone
fissures in this wall are rarely found.
The Eustachian tube begins with an opening in the anterior wall separating
the tympanic cavity from the internal carotid canal.
An opening in the upper part of
the posterior wall leads to the mastoid antrum
(aditus ad antrum mastoideum).
The internal wall separates the tympanic cavity from the internal ear. It is marked by a gentle eminence, the *
promontory
(promontorium), corresponding to the basalturn of the cochlea. Above and
behind the promontoryis an oval window or the fenestra vestibuli which leadsinto the vestibule and is closed by the foot plate of the stapes. Behind and below the promontory in a niche is a round window or the fenestra cochlea which leads intothe cochlea, and is filled with a thin membrane, the secon dary ympanic membrane. '
On the internal wall above the
oval window is a bony torus—the horizontal part of the facial nerve canal. On reaching the entrance to the antrum, the
facial nerve canal turns downwards to form a
descending knee, then passes
behind the posterior wall of the auditory meatus
and through the stylomastoid
foramen to the base of the skull. The
walls of this bony canal may be eroded; in such
cases, the middle ear mucosa may come
through fissures into direct contact with the sheath of
the facial nerve. This sometimes causes the
development of facial paresis and paralysis
in suppurative otitis media. Somewhat behind and above the facial nerve canal, on the inner wall of the aditus ad antrum, lies the peak of the horizontal
semicircular canal the clear contour of which serves for
orientation in operations on the middle ear.
The external wall of the
tympanic cavity is formed by the tympanic
membrane, and above the drum—by the external bony wall of the epitympanic recess or
attic.
The tympanic cavity contains the
three auditory ossicles—the malleus, the incus
and the stapes (Fig. 5)—which are interconnected
by joints and ligaments to form a continuous and
rather flexible chain between the drum and the
oval window. The handle of the malleus is woven, as it
were, into the fibrous layer of the tympanic membrane, and the foot plate of the stapes is fixed in the oval window by means of an annular ligament. The incus lies between the malleus
and the stapes. The whole system is kept in
place by ligaments fastening the malleus and incus to the walls of the tympanic cavity.
The tympanic muscles. There
are two muscles in the tympanic cavity: (1)
The tensor tympani muscle which stretches the tympanic membrane. It lies in the
bony canal above the Eustachian tube, and is attached to the handle of the malleus.
(2) The stapedius muscle which arises from the posterior wall of the tympanic
cavity and is attached to the head of
the stapes by a slender tendon. The
tensor tympani is innervated by a branch of the trigeminal nerve, and the stapedius muscle by a branch of the facial nerve.
The Eustachian or auditory tube which is about 3.5 cm in length connects the tympanic cavity with the nasopharynx. The upper third of this tube, adjoining the tympanic cavity, has bony walls, while the remaining lower portion leading into the nasopharynx
is made up of membrane and cartilage. The
movement of the cilia of the ciliated epithelium
lining the Eustachian tube is towards the
nasopharynx. At rest, the Eustachian
tube is in a collapsed state, but with each
swallowing movement it opens by contraction of the soft palatal muscles attached to it, to let air into the tympanic cavity.
The mastoid process located just behind the external auditory meatus is a bony structure
protruding downwards with the sternocleidomastoid muscle attached to it. In young children, the mastoid process
is not fully developed and represents a bony
tubercle behind the osseous tympanic ring.
The upper border of the process is
the temporal line (linea
temporalis), a bony torus which is a backward extension of the zygomatic
process. The floor of the middle cranial
fossa usually lies on a level with this line.
The anterior wall of the mastoid process is the posterior bony wall of the external auditory meatus.
Behind the spot where the superior wall of
the auditory meatus merges with the posterior wall, there is a small bony peak or the suprameatal spine (spina supra meatum) lying
above the external auditory meatus. Behind the spine there is a smooth depression, the mastoid fossa (fossa mastoidea). The suprameatal spine and the temporal line are important landmarks in surgical operations; the mastoid antrum (antrum
mastoideum) lies on the projection of the mastoid fossa (fossa mastoidea) in the depth of the mastoid process.
The internal wall of the mastoid process abuts upon the
labyrinth, and more posteriorly is bordered by the
post-cranial fossa. On the surface facing the
post-cranial fossa there is a rather wide S-shaped groove, the sigmoid sulcus, containing
part of the sigmoid sinus of the dura mater. The
central part of the mastoid process is
the antrum lying just behind the epitympanic recess. The antrum communicates with the tympanic
cavity and the air-filled cells of the mastoid process. The superior wall or roof of
the antrum separates it from the middle cranial fossa.
The following types of structure are to be found
in the mastoid process: the pneumatic or
large-celled, the diploic and the compact or "sclerotic". In the case of
pneumatic structures, the cavity of the mastoid process is divided by thin bony partitions into a lattice of larger and smaller cells. The diploic structure
has tiny cells resembling a diploetic bone; the most frequent is the mixed form of mastoid structure where smaller cells are to be found alongside bigger ones. In compact structures the bone is indurated and the cells are
very few; this structure frequently occurs as
a result of chronic suppurative otitis media.
-The walls of the tympanic
cavity, antrum and mastoid cells are lined with a continuous thin mucosa
devoid of mucous glands. The mucous
membrane of the Eustachian tube and of the
adjoining part of the tympanic cavity
floor
is covered with ciliated columnar epithelium; the mucosa of the cartilaginous
part of the Eustachian tube contains mucous glands which are absent in the mucosa of the other parts
of the middle ear.
The middle ear is supplied with
blood mainly by branches of the external
carotid artery. Venous blood drainage from the middle
ear is maintained by the veins of the dura mater, the venous sinuses and the venous plexuses round the carotid
artery. Lymph drainage is carried out in two ways: (1) through the lymphatic vessels of the Eustachian tube to the retropharyngeal lymph nodes and further to the deep cervical glands; (2) through the lymphatic vessels across the tympanic cavity to the lymphatic ducts of the external auditory meatus and
the lymph nodes in front of and behind the auricle.
The nerve supply of the middle ear is through branches of the glossopharyngeal, facial and sympathetic nerves.
Internal Ear or Labyrinth
The internal ear consists of
membranous and bony labyrinths, the latter
surrounding the former like a capsule. The
membranous labyrinth is filled with fluid known as endolymph, while around it and
separating it from the bony shell is the
spinal fluid known as perilymph.
The bony labyrinth is made up of
the vestibule, three semicircular canals
and the cochlea (Fig. 6).
The vestibule (vestibulum) lies in the centre of the bony labyrinth
on whose external wall is the oval window; on the opposite, internal wall,
there are two recesses for the two membranous
sacs of the vestibule.
The front sac known as the saccule (sacculus)
communicates with the membranous
cochlea lying before the vestibule, while the
rear sac or utricle (utriculus) is connected with the three membranous semicircular canals passing behind and above the vestibule. The intercommunicating sacs of the vestibule contain the statokinetic
receptors or maculae acusticae, otolithic organs
made up of a highly-differentiated specific neuroepithelium covered with a
membrane containing granules of carbonate and phosphorate
of lime, i.e. the otoliths.
Fig. 6. Bony Labyrinth on Right Side
(1; frontal semicircular canal; (?) ampulla of
frontal semicircular canal; (3) apex of cochlea; (4)
medial turn of cochlea; (5) apical turn of cochlea; (6) basal turn of cochlea; (7) round window; (8) oval window;
(9) ampulla of sagittal semicircular canal; (10) sagittal
semicircular canal; (11), (12) crura; (13)
ampulla of horizontal
semicircular canal; crus commune of frontal and sagittal semicircular canals
The semicircular canals are set at
right angles to each other and represent
the three planes of space. They are three in number: the external or
horizontal, the superior or frontal, and the
posterior or sagittal. One end of each canal opens out into a larger space known as ampulla,
the other end is even. The frontal and sagittal canals have a
common even stem (crus commune).
The jynpulla
of each membranous canal contains a ridge. the crista ampullaris, which is a receptor, i.e. a nerve ending consisting ot a highly-differentiated neuroepithelium or hair and
supporting cells.
The free surface of the hair cells
is covered with hairs which respond to the
slightest displacement or pressure of the endolymph.
The receptors of the vestibule and
semicircular canals are the peripheral nerve endings
of the vestibular analysor.
Fig. 7. Organ of Corti (Schematic View)
(1) basilar membrane:
(2) tectorial membrane; (3), (4) hair
cells; (5) supporting cells; (6) nerve fibres reaching
hair cells
cate at the apex of the cochlea through a small opening known as the helicotrema Both channels are filled with perilymph. ''
The scala vestibuli communicates
with the vestibule, j while
the scala tympani borders on the tympanic cavity <
through the round window covered by the secondary
tympanic membrane.
The scala vestibuli
of the cochlea contains the thin Rei sner's membrane which extends from the
osseous spirn
lamina to cut off a small membranous canal of trianguli> section filled
with endolymph and known as the cochles
duct or ductus
cochlearis.
The organ of Corti (Fig. 7.), a complex
receptive stru ture of the auditory analyzor, rests on the basilar
membrai (membrana basilaris), the lower wall of the ductus cochleii ris.
The basilar membrane is
an arrangement of elastu fibres of different lengths strung from the edge of the bony spiral lamina to the opposite, outer wall of the cochlea.
The organ of Corti has a very complex histological structure containing hair cells and supporting cells. The sensory cells covered with hairs are situated in small groups between the supporting cells. The cells are covered with a membrane called the tectorial membrane
(membrana tec-toria).
The sensory hair cells are surrounded by a
network of cochlear nerve branches leading to the spiral ganglion
of the auditory nerve in the bony spiral lamina and
further by intricate routes to the brain cortex.
PHYSIOLOGY OF THE ÅAR
The ear is one of the sense organs
by which man communicates with the outer world.
I.P. Pavlov's theory of the sense organs presents them as analyzors, each making up a single system
of the following components: (1) the
peripheral part or receptors, i.e. nerve endings
adapted to respond to certain types of stimulation;
(2) nerve conductors to convey the impulse from the receptor; (3) a central
department in the brain cortex for a thorough
analysis of all stimuli and their transformation
into sensations.
Auditory Function
The auditory function of the ear
consists in the conduction of sounds
through the external and middle ears.or cranial bones"and their reception by the
spiral organ of Corti, the receptor of the auditory analyzor. The
external and middle ears make up the
sound-conducting apparatus, whereas the internal
ear, specifically, the organ of Corti, belongs to the sound-perceiving apparatus.
The auricle in man is of lesser
importance than in animals, and yet there is
no doubt that it plays a certain role in collecting
sounds and determining
their direction.
The external auditory meatus conducts sound waves from the outer medium to the tympanic membrane. The mea-tal diameter has nothing to do with hearing acuity. Its atresia, however, as well as
its complete obstruction, as occurs in earwax impaction, hinders the passage of sound waves and considerably impairs the hearing.
Sound
waves
striking the tympanic
membrane set it to vibration. The drum being onnected to the handleof the malleus, these vibrations are transmitted
to the ossicular chain; and the foot
plate of the stapes, closing the oval window of the
labyrinth, rocks in and out of the oval window
according to the phase of sound vibrations. The vibration of the foot plate of the stapes in the oval window sets up vibrations in the perilymph. These
vibrations are transmitted to the basilar membrane and the organ of Corti which it supports.
The vibration of the basilar membrane causes the hair cells of the spiral organ of Corti to get in
touch with the overhanging tectorial membrane. At the same time, the
mechanical energy of vibrations changes into the physiological process of nervous excitation which is conveyed to the most delicate receptors of the auditory nerve to be passed further to its nuclei in the medulla oblongata and through appropriate
canals to the cortical auditory centres in the temporal brain lobes where nervous impulses are interpreted as sounds heard.
The internal ear performs the most
important functions of the ear, because it is here
that sound perception takes place.
Normal hearing depends on the
normal condition of the apparatus for sound
perception and conduction.
The tension of the drum and the ossicular chain necessary
for normal sound conduction is maintained by the combined
action of the tympanic muscles. For normal vibration
the tympanic membrane requires a constant equilibrium
between air pressure in the middle ear cavity and in the outer air, that is on both sides of the
drum. This is maintained by the passage of
air through the Eustachian tube during swallowing. Disturbance of air supply to the middle ear through the Eustachian tube
causes air in the middle ear to be sucked in and the
drum to be indrawn, which is followed by
deterioration of hearing. The normal condition of
the sound-conducting apparatus is extremely important
for the transmission of low tones to the labyrinth, that is, sounds with a low frequency of vibrations per second.
There are two ways of conducting sound waves to
the labyrinth: air conduction (through the external
auditory meatus, the tympanic membrane and the chain of ossicles) and bone conduction (directly through the cranial
bones and the stapes).
High tones, i.e. sounds of a high
vibration frequency per second, are easily conducted
to the labyrinth not only through the tympanic
membrane and the ossicular chain, but through the cranial bones and the stapes as well.
Man can hear external sounds with
a frequency of 16 to 20,000 cycles per second,,
The human ear can differentiate
between sounds of different pitch, intensity and
timbre. There are a number of theories which seek to
explain the essence of hearing and the ability of
the ear to differentiate between sounds. The oldest and most widespread among
them is the resonance theory advanced by Helmholtz in
1863 and based on the physical phenomenon
of sympathetic vibration. According to this theory
the fibres of the basilar
membrane vibrate in unison with sounds,
similar to the action of strings in certain musical
instruments, such as the piano or the harp. The short, thin and tighter fibres of the basilar membrane
which lie in the basal turn of the cochlea vibrate in unison, i.e. resonate
when stimulated by a high tone, whereas the longer, thicker and less taut fibres in the
apical turn of the cochlea resonate in response
to low tones.
There are a number of serious
objections to the resonance theory as it
oversimplifies the essence of hearing as a physiological process by describing it from the mechanical aspect alone, and fails to give a picture of the physiological properties of the auditory analyzor as a
whole. It should be noted, however, that
the localization of perception of high and low
tones in the basal and apical cochlear turns respectively, on which the resonance theory is based, has been confirmed by experiments and clinical observations.
In opposition to the resonance
theory so-called telephonic theory of hearing
asserts that the basilar membrane vibrates all over like a telephone membrane. It denies any analysis of sound being made in the peripheral receptor contained in the cochlea. This concept has been disproved by clinical practice and experimental research.
The first to prove beyond doubt
that sounds of different pitch are perceived
in different parts of the cochlea wasL.A. Andreyev by experiments with conditioned reflexes made in I.P. Pavlov's laboratory. The experiments were made on dogs which
developed conditioned reflexes of salivation
to tones of low, moderate and high frequency. After the reflex had been firmly established, the cochlea on one side was completely destroyed, and the animal retained its conditioned reflex. This was followed by a selective destruction of different parts of the cochlea.
Destruction of the cochlear apex with a thin drill caused disappearance of the conditioned reflex to low-pitched sounds, whereas destruction of the cochlear
base was followed by disappearance of the
reflex to high-pitched sounds. These experiments have
proved that an injury to the apical turn of the
cochlea causes loss of low tone perception, whereas an injury to the basal turn
of the cochlea is accompanied by loss of
high tone perception.
Thus, according to the teachings
of I.P. Pavlov and his followers, the peripheral receptor of the auditory analyzor
makes a primary analysis of sound by converting
the latter's mechanical energy into the physiological
process of nervous excitation. This, in
turn, is conveyed through nerve canals to appropriate centres in the brain cortex where the
nerve impulses are finally interpreted as sounds heard. I.P. Pavlov's teaching gives a clear idea of the functions of each part of the auditory analysor, thus
presenting the latter's entire activity as a
single physiological process.
The faculty of locating the origin
of sounds, the so-called ototopia
depends upon binaural hearing. It is
largely lost in people with unilateral hearing, who have
to turn their heads in various directions to locate the
origin of sound. People with two healthy
ears can easily determine the direction of
sounds without turning their heads.
The ability to find the direction
of sounds is a function of the central
nervous system. If a sound comes from one side,
it arrives at the ear on the other side with an insignificant delay of 0.0006 sec.
This delay makes it possible to
'determine the direction of sound.
Orientation of the body and its
individual parts in space is made possible by
co-operation of many receptors. Apart from eye-sight,
the location of the body and its parts is identified
through nerve endings lying in the skin, as
well as in the muscles, joints and tendons, which are called proprioceptors.
In addition to the above-mentioned
receptors, the cerebellum and, above all, the vestibular apparatus perform an important function in body orientation and in maintaining equilibrium at rest and in motion. The vestibular apparatus consists of
the vestibule containing the otolith system and the semicircular canals with their ampullae
containing the nerve endings of the vestibular analysor.
The accelerations imparted to the
body during its movement in space are
adequate or specific stimulants for the nerve endings of the vestibular analyzor. Movements along a straight line cause
displacement of the otoliths and stimulate the receptors of the otolith, or
statolith, structure contained in the vestibular sacs.
Angular or rotatory motions are followed by displacement of the endolymph
in the semicircular canals and stimulation of receptors
in the ampullae.
Stimulation of the receptors of
the vestibular analyzor
produces a number of reflex reactions which
cause a change in the tonus of some muscle bundles of the torso, extremities, neck and eyes. This, in turn, causes the whole body to change position and maintain balance.
One of the unconditioned reflexes
observed in stimulation of the semicircular canals is
nystagmus which consists in a rhythmic movement of the eyes in a certain direction and back, such as lateral and vertical nystagmus.
Nystagmus may be observed in different positions of the eyeball,
for example, in gazing straight ahead and in an extremely
side-long glance. The observation of nystagmus !S used to assess the reaction of a stimulated vestibular apparatus.
The role of the vestibular apparatus
becomes particularly apparent during an acute
disturbance or cessation of *ts
function, which occurs in some diseases. The patients
suffer from severe static and dynamic disorders: they
are unable to stand, walk and sit; they cannot
co-ordinate their movements, develop
spontaneous nystagmus, etc. This is accompanied by vertigo,
nausea and vomiting. Three to four weeks later
these symptoms subside due to compensation from the central systems. A more or less intensive
reaction of the vestibular apparatus to adequate, i.e. specific, stimulation depends on the state of
the central nervous system, its higher division, the brain cortex, in particular.
This examination begins with collection of data on the case, followed by inspection
of the ear and a functional examination of hearing. In a
complex examination nose and throat, the latter
two are always be dealt with.
A case history must include an
account of the symptoms as described by the patient,
and the circumstances under which the
illness began.
In gathering this information attention should be paid to (a) ear pain and its character; (b) pus discharge; (c) deterioration of hearing or total deafness; (d) tinnitus; (e) dizziness. It is equally important to find out whether the patient complains of headaches, chills, etc. Among the numerous causes of ear diseases the most frequent are inflammations in the nose and throat which produce acute otitis media. Therefore, it is important to know if the ear disease in question was preceded by influenza, acute rhinitis, etc. Then general details should be obtained, i.e. information about the general state of health, past diseases, infectious ones in particular, working and housing conditions, and other facts relating to the everyday life of the patient. Examination of the ear includes an external examination and palpation of the ear and the mastoid process,
as well as inspection of the external auditory meatus and the tympanic
membrane (otoscopy).
-
Otoscopy
Examination of the external
auditory meatus and the tympanic membrane,
as well as the tympanic cavity when the drum is
absent, requires artificial lighting and a head mirror (Fig. 9) to reflect the light into the ear and the ear speculum (Fig. 10). The best source of illumination is a 50 to 60 W frosted bulb; the head mirror is a round slightly concave mirror 8 to 9 cm in diameter with the focal length of 20 cm
and a hole in the middle. In the absence of
electric lighting, any source of illumination including daylight should be used. The examination is made in a sitting posture with the light placed on a level with the patient's
head,
to the right and a little behind, as shown in Fig. 8. The head mirror is so fixed before the examiner's left eye that the eye, the mirror hole and the ear under examination are in one straight line.
Both eyes are used when making an otoscopic examination, the left
eye necessarily peering through the mirror hole. Before inserting the ear speculum, one should examine the meatal opening and measure its diameter.
Little children are examined with the aid of an
assistant who keeps the child's head firmly
pressed to his breast with one hand, and holds its
arms with the other. The legs of the child are
pressed between the legs of the assistant.
The ear speculum with its dilated
part held between the thumb and the forefinger is
carefully introduced into the meatal opening with a gentle rotation to a depth of 1 to 1.25 cm without touching the bony part, in so far as is practicable. At the same time, the pinna is
pulled upwards and backwards in adults and
downwards and backwards in small children to straighten out the angle of the meatus. Where there are
swellings, fissures or eczema, the speculum
should be introduced with particular caution to avoid pain. Lightly moving or tilting the inner part of the speculum, the examiner inspects in turn the internal parts of the auditory meatus and
the entire surface of the drum. In examining the
meatal canal major attention should
be given to the posterosuperior wall to detect
possible thickenings and even considerable overhangings extending downwards and outwards.
It is possible to examine the ear
without the aid of artificial lighting only
in cases of a sufficiently wide and fairly
straight auditory meatus. To avoid
obstructing the light with his own head, the
doctor should be at some distance from the
patient, although ear details will not be
seen so clearly.
The normal drum is an oval disc of
a pearly grey colour on which the following landmarks
are clearly visible (Fig. 3, coloured
Table I, Fig. 1). A whitish-yellow knob, the size
of a pin-head, projecting from the anterosuperior
part of the drum is the short process of the malleus. Two grey-isk-white streaks extending
backwards and forwards from it are the anterior
and posterior folds separating the anterosuperior part of the drum, the
pars flaccida of Shrap-nell,
from the lower tense part, the pars tensa. From the short process the handle of the malleus can be
seen extending downwards and backwards. Its
broader lower end terminates at the centre of
the drum, the umbo. At otoscopy, the light rays from the mirror form on the drum a brilliant cone-shaped
light reflex with the top pointed to the centre (umbo) and the base facing the
anteroinferior edge of the tympanic membrane.
For convenience, in describing
changes on the tympanic membrane, the-latter
is divided into four quadrants (Fig. 3) by an
imaginary line extending the malleus handle to the edge of the drum and by an intersecting line drawn at right angles to the first through the centre of the umbo; thus forming
the anterosuperior, anteroinferior,
posterosuperior and posteroinferior
quadrants. The drum is very closely connected
with the tympanic cavity; therefore, it will
reflect any existing morbid condition of the middle ear. Thus, a change in colour, for instance, redness of the drum, indicates otitis media.
Changes in location of the landmarks, the light
cone in particular, manifest themselves in cases
of drum retraction resulting from chronic diseases of
the middle ear.
The mobility of the drum may be tested by the use of a pneumatic speculum (Fig. 11). The dilated end
of this speculum is hermetically sealed with a lens, and
a tube branching from its side is attached to a rubber bulb. To facilitate observance of drum mobility through the lens, the speculum is tightly fitted into the auditory meatus, the air being alternately
compressed and rarefied with the rubber bulb, causing
the drum to move in and out. At otoscopy the examination begins with the
healthy ear in order to compare it with its diseased counterpart.
Examination of the Auditory Function
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Fig. 12. Noise-box |
The functional examination of hearing is made by means of whisper and conversation voice, tuning forks and audiometers. The whisper test should be carried out in a quiet room of
adequate size. Each ear is examined separately, while the other ear is closed with a finger tip. The patient turns the ear to be tested to the examiner so that he does not see the letter's face and cannot guess his words by watch- ing the lip movements. The whisper should
always be of the same intensity obtained by
breathing out effortlessly and using the
residual air to call out words.
The normal ear can hear whispered speech with a
prevalence of low tones, i.e. consonants, labial and
palatal sounds, b, p, t, m, n, at a distance of 5 to 10
m; whispered speech with a prevalence of high
tones, i.e. sibilants, s, z) ch, sh, shch, is heard at a distance of up to 20m. Estimation of hearing by the whisper test may be made by calling out numbers from one to a hundred and selecting numbers with low sounds, such as two, five, nine, and with Qigh sounds, such as six, seven,
sixty-six, etc. As the figures uttered can be easily guessed by some patients,
the hearing test should rather be made with
specially selected words of high and low tones. A
table of such words has
been compiled by V.I. Voyachek.
The first group of words primarily contains low
sounds heard at a distance of 5 m on the
average; the second group is mainly composed of high
sounds heard at a distance of 20 m. The following is a
conjectural selection of English words based on the same principle.
By using this table one may roughly determine the nature of the ear disease. A poor perception of words of the first group (low tones) will indicate a defect in the sound-conducting apparatus, i.e. conduction deafness. Impaired hearing of words from the second group (high tones) will point to a lesion in the sound-perceiving apparatus, i.e. nerve deafness. If whispered speech is heard at a di- stance of 6 to 8 m,
the hearing is practically normal. If the patient
does not hear the whispered speech at all, conversation
voice or forced voice tests should be used. In examining unilateral deafness it is not enough to close the normal ear with a finger tip to shut out all sound. Therefore, a
special noise-box (Fig. 12) is put into the normal ear to exclude its hearing altogether.
Other methods of excluding the
normal ear, such as rubbing the pinna with the flat of the open hand or shaking the
finger plugging the auditory canal are
less reliable.
Tuning fork tests.
Hearing acuity is determined by the whisper
test with comparative ease and quickness. But the differential diagnosis between the conduction and
perception types of deafness, as well
as a more accurate determination of
hearing acuity is made by using tuning forks (Fig. 13). The tuning fork produces a clear tone without overtones. The human ear can hear in a sound range
of 16 to 20,000 cycles per sec. The
highest and lowest tones perceptible
to the human ear indicate the higher and lower limits of hearing respectively. The tones heard between the upper and lower limits of hearing make up the
so-called audible range or register.
This range decreases noticeably with
age, mostly due to reduction of the upper limit of hearing. A set of tuning forks can be used to examine hearing
acuity for different tones, from 64 to 4,096 cycles per sec, as well as to determine air and bone conduction. To estimate air conduction, a sounding
tuning fork is held near the meatal opening. When bone conduction is being determined,
a sounding tuning fork is placed on
the head or the mastoid process. In
normal hearing air conduction is
better than bone conduction. In medical practice, bone and air conduction is
examined only with two tuning forks,
of the types C128 and C'2i048. The following experiments can help in a differential diagnosis
between the conduction and perception
types of deafness.
The Weber test of
sound lateralisation (Fig. 14a). A C128
tuning fork is" sounded and
placed on the vertex, and the patient
is asked to say in which ear the sound is heard best. In case of conduction deafness, such as caused by earwax impaction in
the auditory meatus or otitis media, the sound will be best heard in the diseased ear. In the event
of
nerve deafness, the tuning fork will be best heard in the normal ear.
^" The Rinne tesi or comparison between
bone and air conduction (Fig. 14b). When_a sounding C3La8JLuningjfork
applied to the mastoid
process" can no longer beTTeanT, it~is~hil(rto the_ear;
it then appears Jhat_the_soiind is heard longer byair Conduction than by ~bone~conduction. normally for &1) to 90 sec compared~"to
45 sec in the casejii Bone conduction. In such circumstances^—the~^lnnltest
is considered positive (Rinne+);
a positive Rinne is observed
in patients with normal hearing, as well as in those with
nerve deafness, jn conduction deafness the jiutalion of bone_conduction_inay_^e_gaual to thatof
air conduction or~even~exceed~it^considerablY, in Iwhich_"caseTEiIIBinna test~Ts~coBsidered
Taegative
(Rinne —).
The Schwabach test compares the duration of
bone conduction from the vertex or the mastoid process of the patient with the normal bone conduction of the examiner. In conduction deafness, bone conduction is lengthened, whereas in nerve deafness it is shortened.
The acuity of hearing for high
tones is determined with a G4
tuning fork of 2,048 cycles per sec. A certain high tone loss is noticeable in deafness due to old age and in nerve deafness.
A more accurate and quicker examination of hearing is made with a special instrument
called the audiometerwhich can be used
to estimate hearing acuity within the entire
tone range important in the estimation of hearing.
Examination of tho Vestibular Fiinrtinn
Examination of the vestibular function
is preceded by questioning and examining the
patient. Patients with vestibular
disturbances usually complain of giddiness, unstready gait, as well as occasional sickness and vomiting. Examination of the patient may reveal a nystagmus
often associated with a functional vestibular disturbance. Vestibular nystagmus
may be observed in a patient looking sideways and
sometimes in a patient staring straight ahead. Disorders
in co-ordination, static equilibrium and balance of walking are
also likely to happen.
Special clinical tests are used to examine the vestibular function. These
tests are based on procedures for artificial stimulation of the vestibular receptors to produce nystagmus. There are three basic tests of this kind,
the rotation, caloric and compression tests.
The rotation test involves
turning the patient's body around the vertical axis to cause endolymph movements in the semicircular canals, which stimulate the
receptors and produce nystagmus.
The patient is seated in a chair (Fig. 15) which can be rotated horizontally and is revolved at a speed of 10 revolutions in 20 sec. This stirs up the endolymph in the semicircular canals. When the chair is stopped
abruptly after rotation to the right, the patient will have leftward nystagmus; Fig. 15. Rotating Chair if the procedure is
reversed the
nystagmus will be in the opposite direction. So that the
nystagmus may be studied, the patient is directed to look at the examiner's finger, which is held at a distance of 30 cm towards the side where the nystagmus
is expected.
In most people with normal vestibular sensitivity the duration of post-rotational nystagmus is, on
the average, 30 to 35 sec. Among the disadvantages
of this test is that rotation stimulates
both labyrinths, though with unequal force.
The caloric test is based
on the phenomenon of endolymph movement in the semicircular canals under the effect of cooling or heating by artificial means.
During this test each labyrinth is
examined separately. Each ear in turn is
syringed with water; a cold douche at 16° to 30
°G causes nystagmus to the side away from the ear being tested, whereas a warm douche at 38° to 41 °C causes nystagmus in the
opposite direction.
Absence of nystagmus
in the caloric test may indicate a loss of vestibular sensitivity.
In case of dry perforation one
should abstain from the caloric test for fear
of provoking a relapse of suppurative otitis.
Some pathological conditions of
the labyrinth are likely to produce a nystagmus caused by air compression or rarefaction in the auditory canal. This is known as the compression test. If
there is a fistula or a bone defect in a labyrinth
wall (external semicircular canal), the air compressed
with a bulb in the auditory meatus causes
nystagmus towards the
diseased ear, whereas aspiration produces nystagmus to the opposite side. This phenomenon is called the fistular symptom.