RADIOLOGICAL EXAMINATION OF THE LIVER, BILIARY TRACT AND PANCREAS.
THE BILIARY TRACT
A wide variety of techniques for imaging the biliary system now exist. These include:
1. Simple X-rays
2. Oral cholecystography
3. Intravenous cholangiography
4. Operative and postoperative cholangiography
5. Percutaneous transhepatic cholangiography (PTC)
6. Endoscopic retrograde cholangiopancreatography (ERCP)
7. Ultrasound
8. Isotope scanning
9. Computed tomography (CT)
10. Magnetic resonance imaging (MRI).
In many cases the clinical features point clearly to disease of the biliary tract. Thus with clinical symptoms of biliary colic or with obstructive jaundice there is little doubt as to the system to be investigated. In other cases, however, the symptoms are more vague, and may merely consist of dyspepsia or other indefinite abdominal symptoms.
In current practice, the primary investigation of suspected gallbladder or bile duct disease is by simple X-ray or ultrasound or both.
Simple X-rays off the biliary trad
Opaque gallstones will be readily shown, but unfortunately comprise only 30% of the total number. These vary in type They may be large laminated structures, which are usually solitary or few iumber. On the other hand small calculi may be multiple and numerous. An opaque stone in the cystic or common bile duct can be diagnosed by its position relative to the normal gallbladder. This is easy if there are also opaque stones in the gallbladder.
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Fig. Different types of biliary calculi in the gallbladder. (A) Large and (B) small mixed stones with translucent cholesterol centres, (C) infective stones with dense calcium carbonate deposits.
Occasionally calcification may occur in the wall of a chronically diseased gallbladder – the so-called ‘porcelain gallbladder’ outlined at simple X-ray.
Gas in the biliary tract, usually in the hepatic ducts, is only occasionally noted at plain X-ray. This implies either a fistula between the bowel and the biliary tract, or an incompetent sphincter of Oddi. The latter condition may be seen following passage of a large calculus or following operative intervention and exploration.
It is important to remember that both oral and intravenous cholecystography are unlikely to be successful in the presence of obstructive jaundice. This is because with biliary obstruction the excretion of contrast from the liver is impaired.
Fig. Calcification of the gallbladder wall.
Fig. Gas in the biliary ducts.
Oral cholecystography
This was for many years the most widely used technique for imaging the gallbladder, but has now been largely replaced by ultrasound.
The technique for oral cholecystography requires the patient to take the contrast medium by mouth the evening before the examination. He remains on a fat-free diet until he attends for X-ray examination some 16 hours later. At this stage the gallbladder is usually well filled with contrast. Once this has been verified the patient is given a fatty meal.
This will induce contraction of the gallbladder within 10 to 30 minutes. Further films are then taken which show the normal gallbladder to have contracted well, and may demonstrate the contrast-filled cystic and common bile ducts, and the entry of contrast into the duodenum.
Non-opaque calculi lying in the gallbladder will be demonstrated of gallbladder disease, or of obstruction of the cystic ducts by calculus, but is not conclusive. This is because excretion by the liver depends on absorption of the contrast medium by the alimentary tract. A proportion of patients have diarrhoea following ingestion of the oral medium and the amount absorbed from the gut is therefore unpredictable. In patients with severe liver disease or with biliary obstruction excretion from the liver may also be impaired.
Tumours of the gallbladder. Carcinoma of the gallbladder is diagnosed on clinical grounds and radiology, including cholecystography, has proved of no assistance in arriving at a diagnosis. However ultrasound, CT and MRI may be helpful, particularly in staging. Benign tumours of the gallbladder are occasionally seen and these can be diagnosed by cholecystography. Papillomas are seen as small translucent defects at the lateral margin of the gallbladder, whilst adenomas are seen as small translucent defects attached to the fundus. Carcinoma of the common bile duct usually presents with obstructive jaundice and is diagnosed when direct cholangiography or ultrasound shows a typical obstruction to the dilated common duct.
Intravenous cholangiography
This was widely practised at one time but toxic reactions were not infrequent and it has been rendered obsolete by ultrasound and CT.
Fig. Contracted gallbladder after a fatty meal with filling of the cystic and common bile ducts and entry of contrast into the duodenum.
Ultrasound
This is now widely used as the preliminary examination in suspected gallbladder or biliary tract disease and has the added advantage that the liver and pancreas can be assessed at the same examination. It is highly accurate in the diagnosis of gallstones including the nonopaque stones not visible at simple radiography. Gallstones characteristically produce high density echoes and cast acoustic shadows appearing as dark bands.
Ultrasound will also demonstrate dilated intrahepatic bile ducts or a dilated common bile duct and thus will help to differentiate obstructive from non-obstructive jaundice.
Fig. Gallstones. Note the acoustic shadows causing dark bands behind the gallbladder. L ■ liver. GB = gallbladder with stones. AC = acoustic shadows.
Fig. Dilated intrahepatic bile ducts shown by ultrasound.
Isotope scanning
“Tc99m HIDA (a derivative of iminodiacetic acid (IDA)) is a drug which is concentrated by the hepatocytes and excreted in the bile. Serial gamma camera pictures taken at 10-minute intervals after administration show the normal gallbladder and biliary tract at 30 min and drainage into the gut at 60 min (Fig. 9.8). In biliary-obstruction there is no evidence of gut activity even on delayed films at 24 h. HIDA is also a most valuable screening test for acute cholecystitis when the gallbladder will fail to fill despite gut activity. Similar appearances are seen if the cystic duct or Hartmann’s pouch are obstructed by calculi.
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Fig. Biliary scan (99Tcm H1DA). Serial films. (A) 5 minutes, (B) 10 minutes, (C) 15 minutes, (D) 20 minutes, (E) 25 minutes and (F) 30 minutes after injection. Contrast is seen in the bowel at 20 minutes. Note concentration in gallbladder from B onward.
Operative and postoperative cholangiography
It is well known that in calculous biliary disease cholecystectomy alone will leave a proportion of patients with residual stones in the biliary ducts. On the other hand exploration of the ducts adds considerably to the risk of the operation and may miss stones which are free to move about in the ducts or are of soft consistency (‘putty stones’)- Many surgeons now perform operative cholangiography as a routine at operations for biliary stones. A small tube is inserted into the cystic duct and the bile ducts are filled with contrast medium. Films are obtained and examined during the operation and should demonstrate most removable calculi in the ducts. Operative cholangiography, if skilfully performed, adds little to the operative time and will ensure against leaving stones in the duct which may require a second operation. The best results are obtained when there is direct cooperation between surgeon and radiologist and apparatus permitting serial films is used. The possibility of artefact due to gas bubbles must be borne in mind and guarded against.
Postoperative cholangiography is carried out in the immediate postoperative period by injecting the T-tube drain in the common bile duct with contrast medium (Fig. 9.9). This method will also show residual calculi which have been missed at operation. These can be removed with a catheter snare passed through the T-tube tract under image intensifier control. Operative and postoperative cholangiography are also useful for demonstrating strictures of the common bile duct and in assessing neoplastic obstruction.
Fig. Postoperative T-tube cholangiogram showing free entry of contrast into the duodenum despite a residual non-opaque calculus at the lower end of the common hepatic duct .
Percutaneous transhepatic cholangiography (PTC)
The main indication for percutaneous cholangiography is in the assessment of obstructive jaundice. If the bile ducts are grossly dilated there is usually little difficulty in puncturing a dilated duct percutaneously. Once a hepatic duct has been entered, bile can be aspirated and contrast medium injected (Fig. 9.10). This enables the site of obstruction to be demonstrated and its characteristics to be studied. A diagnosis of obstructive carcinoma, stone or stricture, can then be confirmed. The puncture is made percutaneously from the right flank using a fine needle and after preliminary infiltration of the skin and subcutaneous tissues with a local anaesthetic. The prothrombin time should not be more than 3 seconds prolonged. Percutaneous biliary drainage can also be performed via a special needle catheter assembly. After a preliminary fine needle percutaneous cholangiogram one of the main ducts is catheterised percutaneously under screen control. The obstructed ducts can then be drained with an indwelling catheter as a palliative measure or as a preliminary to surgery. A further refinement of this technique is the percutaneous insertion of a drain through a stenosis or obstructed common duct into the duodenum.
Endoscopic retrograde cholangiography (ERC) is a technique which is now widely used and has largely replaced PTC. The technique is essentially similar to ERCP described below, and can be performed safely even when the prothrombin time is significantly prolonged.
Fig. Percutaneous cholangiogram in a patient with obstructive jaundice. This patient had a congenital choledochal cyst treated by anastomosis to the gut. This was followed years later by an anastomotic stricture.
Endoscopic retrograde cholangiopancreatography (ERCP)
Under radiological control the ampulla of Vater is cannulated and the common bile duct or pancreatic duct can be entered. Contrast medium can then be injected and the biliary or pancreatic ducts can be shown (Fig. 9.11). Biliary obstruction due to stone or neoplasm can be visualised, or alternatively a normal biliary tree may be shown. In skilled hands this is probably the method of choice for the investigation of obstructive jaundice. It is also of great value in the investigation of pancreatic disease. Not only can the pancreatic duct be injected and shown to be normal, abnormal, or obstructed but pancreatic juice can be directly collected and analysed.
For this examination the patient is usually fasting and lightly sedated. A side viewing duodenoscope or other fibre-scope is passed to the duodenum. The ampulla of Vater is identified and a small Teflon catheter is passed from the endoscope into the apex of the papilla under visual control.
Fig. Normal biliary and pancreatic ducts outlined by endoscopic retrograde cholangiopancreatography
CT and MRI of bile ducts
CT. Normal intrahepatic ducts are not shown at CT, but dilated ducts are, and CT will usually show the site and nature of the obstruction, whether tumour or calculus. It is also invaluable in staging malignant disease causing obstructive jaundice.
MRI. Magnetic resonance cholangiography (MRC) has recently developed as a promising non-invasive technique for assessing the obstructed biliary tract. The pancreatic duct can also be shown, and the obvious advantages over more invasive techniques mark it out as the method of choice for the future
Fig. Magnetic resonance cholangiopancreatography (MRCP) showing dilated common bile (b) and pancreatic (p) ducts due to obstructing cholangiocarcinoma at lower end of common bile duct (arrow), g = gallbladder; L = left.
THE LIVER
The main indications for investigation of the liver by imaging are the diagnosis or exclusion of tumours, primary and secondary, of cysts and of inflammatory lesions. Other indications are the investigation of hepatomegaly, of cirrhosis and of portal hypertension. The techniques available include:
1. Simple X-ray
2. Ultrasound
3. CT
4. Isotope scanning
5. MRI
6. Hepatic angiography
7. Portography.
Simple X-ray provides little information apart from confirming enlargement of the liver and showing the occasional calcified lesion such as some hydatid cysts.
Ultrasound
Ultrasound is widely used in the investigation of the liver and biliary systems. Within the liver, cysts, abscesses, haematomas and neoplasms both primary and secondary are readily identified. Tumours usually show as rounded areas with diminished echoes, though occasionally, as with some colonic secondaries,
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Fig. Normal liver and gallbladder. Longitudinal scan. The gallbladder appears as a well-defined oval transonic organ (black arrow) anteriorly. The diaphragm produces the curved line (white arrow) posteriorly.
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Fig. Multiple small metastases in liver (arrow = halo).
Fig. Multiple liver metastases. Longitudinal scan. The liver is enlarged and there are multiple areas of high echogenicity (arrows), scattered through it indicating metastases. Primary tumour in large bowel.
high intensity echoes are seen. Cysts are completely transonic. As already noted above, dilated bile ducts are identifiable and are characteristic of obstructive jaundice. The gallbladder and gallstones are also readily shown.
Fig. Huge hydatid cyst occupying most of right lobe of liver. C = cyst; K = kidney; D = diaphragm.
Isofope scanning
Following an intravenous injection of “Tcm colloid the normal liver substance takes up the isotope uniformly and is easily imaged. Most pathological lesions – tumours, cysts, abscesses and haematomas -do not take up the compound and appear as filling defects in the opacified liver. Provided the individual lesions are larger than
CT scanning
CT shows the liver in axial sections with high resolution. Primary and secondary neoplasms can be demonstrated and differentiated from cysts. Adjacent organs are also shown on the scans including abdominal nodes thus making CT invaluable in the staging of tumours.
Contrast enhancement following intravenous injection is frequently undertaken to highlight focal lesions. Dynamic scans involving rapid serial images after contrast injection may assist in diagnosing vascular lesions such as haemangiomas and some tumours.
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Fig. (A) Liver metastases. “Tc99m-S colloid scan. Anterior projection. The liver is large and contains many defects caused by metastases.
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Fig. (B) “Tcm cojloid scan of liver. Multiple metastases from carcinoma of the colon showing numerous areas of low attenuation
MRI
MRI is similar to CT in the accuracy of showing focal lesions in the liver. It has the advantage of easy imaging in the coronal and sagittal planes but is still relatively more costly than CT.
Fig. Hepatocellular carcinoma. Most of the right lobe of liver replaced by tumour with rim enhancement after contrast.
Fig. Hydatid disease. Large hydatid cysts in right and left lobe of liver together with daughter cysts.
Angiography
Hepatic angiography is performed by percutaneous transfemoral catheterisation of the coeliac axis or superselective catheterisation of the hepatic artery followed by injection of a bolus of contrast medium. The technique was once widely used for the diagnosis of tumours, but has been superseded for this purpose by the less invasive techniques just described. Angiomas, aneurysms and other vascular lesions can be precisely defined by angiography and the technique is also used for the transcatheter embolisation of vascular lesions as well as tumours. It is also utilised for the treatment of tumours by local chemotherapy drug infusion.
Fig. Selective hepatic arteriogram. A large vascular tumour is shown in the lower part of the right lobe of the liver. Histology: primary hepatoma.
Portography
Portography Portography, or imaging of the portal system, can be achieved in several ways:
1. Splenic portography. This was once widely performed by direct injection of the spleen from a percutaneous needle puncture in the flank (Fig. 9.21), but has been rendered obsolete by other techniques.
2. Arterial portography is achieved by delayed filming after percutaneous catheterisation and injection of the splenic and superior mesenteric arteries allowing time for the contrast bolus to pass through the vascular bed and drain into the splenic or superior mesenteric veins and on into the portal vein. DSA enhances the quality of the resultant images of the portal circulation.
3. Transhepatic portography is performed by passing a needle
catheter assembly through the liver from the right flank and siting
the tip in a portal branch using image intensifier screening control.
The catheter can then be guided to different sites in the portal
system. Normal blood clotting factors are essential and the track in
the liver is embolised with gelfoam on withdrawal of the catheter.
This route is used for demonstration and embolisation of varices and for venous sampling.
The above are invasive techniques. They are gradually being replaced by minimally invasive or non-invasive methods. Thus spiral CT, which requires an intravenous injection of contrast, can demonstrate the major vessels and varices, as can gadolinium-enhanced MRI. Unenhanced MRI can show the major vessels as low signal structures without contrast as can ultrasound.
Fig. Percutaneous splenic phlebogram. The splenic and portal veins are patent and there is good filling of the intra-hepatic branches of the portal vein. There is reflux filling of the oesophageal varices.
LIVER AND PANCREAS
PLAIN FILMS
Aids detection of opaque gallbladder calculi, calcification in the gallbladder wall, gas in the biliary tree and pancreatic calcification.
ORAL CHOLECYSTOGRAM
An iodine-based oral contrast medium is ingested the evening before the examination. Films of the right upper quadrant the following day demonstrate an opacified gallbladder. It does not opacify if there is cystic duct obstruction or the patient is jaundiced. Calculi are seen as filling defects; a film after a fatty meal shows the extent of gall-bladder contraction.
OPERATIVE CHOLANGIOGRAM
This investigation is performed at cholecystectomy when the cystic duct is cannulated and contrast injected to outline the common bile duct. Exclusion of common bile duct stones avoids the need for surgical exploration.
T-TUBE CHOLANGIOGRAM
The examination may be carried out approximately 10 days after surgery to identify any remaining calculi in the common bile duct. Contrast is injected into theT-tube under fluoroscopic control to exclude residual calculi.
TRANSHEPATIC CHOLANGIOGRAM
A fine needle is inserted directly into a bile duct in the liver under local anaesthetic. Contrast is injected to visualize the entire biliary system and thus try and elucidate a cause for obstructive jaundice.
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Fig. Normal T- tube cholangiogram.
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Fig. Normal ERCP examination showing the pancreatic and common bile ducts.
ERCP
After the patient is sedated and the pharynx anaesthetized, an endoscope is introduced and advanced through the mouth into the duodenum, with cannulation and contrast injection into the ampulla of Vater, to demonstrate both the bile ducts and the pancreatic duct. Common bile duct stones can be removed through the endoscope by insertion of a catheter with a basket or balloon. Malignant common bile duct strictures can also be stented.
ULTRASOUND
• Liver ultrasound: the best basic imaging modality for focal or diffuse disease of the liver, staging primary tumours, detecting secondary deposits, investigation of calculi and jaundice and as an aid to liver biopsy or interventional procedures. Ultrasound will visualize the gallbladder, common bile duct, hepatic and portal veins.
• Pancreatic ultrasound: useful for suspected pancreatitis or tumour and to assist pancreatic biopsy.
ISOTOPE SCANNING (99m-technetium HIDA)
The isotope is accumulated by hepatocytes with excretion in bile. After a short transit time in the liver, the isotope is identified in the gallbladder and bile ducts at 15-20 minutes. Bowel activity is generally seen within an hour of injection. Excretion is severely delayed in biliary obstruction.
COMPUTED TOMOGRAPHY (CT)
Ultrasound is the first line of investigation, but if unsuccessful, CT is indicated. It demonstrates the full range of liver and pancreatic disease, including cirrhosis, tumours, pancreatitis and pancreatic carcinoma.
MAGNETIC RESONANCE IMAGING (MRI)
Provides excellent cross-sectional imaging as does CT, but without the risk of radiation. Blood vessels and bile ducts may be shown without injected contrast by using magnetic resonance angiography and magnetic resonance cholangiography.
ANGIOGRAPHY
Pre-operative assessment for the resection of pancreatic and liver tumours; vascular anatomy in portal hypertension.
Fig. 3 D reformat of axial spiral CT images showing portal vein and gastric varies.
Choice off examination in biliary and liver disease
The large battery of tests now available can give rise to over-investigation and careful clinical judgement is required as to which tests should be used in particular circumstances. To some extent this will be conditioned by local availability of apparatus such as CT or ultrasound, and local skills and expertise. However, where all techniques are available, primary investigation should be by non-invasive techniques. The more invasive methods such as percutaneous cholangiography and angiography should be reserved for specific indications. Suspected liver masses (tumours, primary or secondary; cysts and abscesses) should be examined in the first place by isotope scanning or ultrasound. Both these methods will usually demonstrate liver masses quite well. Ultrasound has the advantage that it will differentiate cysts and abscesses from solid masses. CT and MRI will also perform this function but are more expensive investigations and CT involves radiation. They are used for more precise diagnosis; as a prelude to surgery; and for tumour staging.
In suspected obstructive jaundice ultrasound is the primary investigation of choice, though biliary isotope scanning will show moderately dilated ducts, as will CT and MRI. Transhepatic cholangiography or ERCP may be required to define the point of obstruction, and percutaneous biliary drainage may be used in treatment. Stent insertion is also possible using percutaneous or ERCP techniques.
THE PANCREAS
Diseases of the pancreas demonstrable by imaging include inflammatory lesions (acute and chronic pancreatitis), cysts and tumours.
Simple X-ray will occasionally show extensive nodules of calcification in the pancreas associated with chronic pancreatitis but is otherwise of little help.
Barium studies will show distortion of the duodenal loop by masses in the head of the pancreas and large pancreatic masses or cysts may displace the stomach.
Ultrasound. The normal pancreas may be partly obscured by bowel gas but when well seen appears as a 1-
CT is now the method most widely used for the demonstration of pancreatic morphology. The pancreas and its relationships to adjacent organs are clearly identified; cysts and mass lesions greater than
MRI can also show the pancreas well but has no advantages over CT, which is much cheaper and more readily available.
ERCP is widely used for demonstrating the pancreatic duct and its obstruction or stenosis by calculi or tumour. The bile ducts can be demonstrated at the same time and a variety of diagnostic and therapeutic procedures performed. These include:
1. Stone extraction from pancreatic and bile ducts
2. Sphincterotomy
3. Biopsy of ampulla Cytology of pancreatic juice or brushings
4. Balloon dilatation of benign strictures
5. Biliary stent insertion
6. Pancreatic cyst drainage.
Recent advances have made it possible to show the pancreatic duct more readhly by MR. Magnetic resonance cholangiography and pancreatography (MRCP) caow provide good visualisation of dilated ducts non-invasively and will be increasingly used for diagnostic purposes.
Fig. Pancreatic pseudocyst. Longitudinal scans. (A) Low power. The huge pseudocyst is shown as a large transonic mass in front of the aorta and superior mesenteric artery (arrow). (B) High power. The outline of the cyst is better seen (arrow) and a septum and echoes are shown within it.
Fig. Normal pancreas. Note lobulation of outline in obese patient. Arrows point to tail. (L + 10 W 200).
Fig. Chronic pancreatitis. Paraductal cysts deform and enlarge the pancreatic head which appears as a low density area anterior to the right kidney, inferior vena cava, and aorta. Note calcification (L O W 200).
Choice of examination
CT is probably the best method for speedy demonstration of the pancreas. The normal pancreas is usually well shown as are masses and cysts. Small tumours whether carcinomas or islet cell adenomas are more difficult to define. Ultrasound in skilled hands is almost as reliable, but is to some extent operator-dependent. Isotope scanning is less reliable than CT or ultrasound and is no longer used for pancreatic lesions. Neither CT or ultrasound will differentiate an inflammatory pancreatic mass from a tumorous lesion. However, fine needle biopsy guided by CT, ultrasound or MRI will permit a definitive diagnosis.
GALLSTONES
Gallstones are common and occur in approximately 10% of the population with a marked female: male preponderance (4: I).There are three main types: mixed, cholesterol and pigment stones. Predisposing causes include obesity, diabetes, Crohn’s disease, cirrhosis, pregnancy and haemolytic disease (sickle cell, thalassaemia).
RADIOLOGICAL FEATURES
• Plain films visualize approximately 10% of calculi as they are radiopaque. They may be faceted with multiple laminations.
• Ultrasound is the definitive investigation, where gallstones appear as echogenic areas casting a shadow. Gallbladder wall thickening and diameter of the common bile duct can also be assessed. Common bile duct stones are generally not accurately identified.
• Cholecystography is not now widely utilized but may assess function of the gallbladder.
COMPLICATIONS
• Acute cholecystitis: usually precipitated by obstruction of the cystic duct from a calculus.
• Chronic cholecystitis: chronic inflammation results in thickening and fibrosis of the gallbladder; it is frequently shrunken, and non-functioning.
• Biliary tract obstruction: secondary to the passage of a calculus into the common bile duct (choledocholithiasis) with obstructive jaundice.
• Acute pancreatitis: a strong association exists with gallstones. A stone at the lower end of the common bile duct not only impairs pancreatic drainage, but also promotes bile reflux into the pancreatic duct.
• Gallstone ileus: occurs when a gallstone ulcerates into the duodenum via a fistula and causes small bowel obstruction by stone impaction.
• Gallbladder carcinoma: rare, but usually associated with gallbladder calculi.
• Empyema: after a gallstone becomes wedged in the cystic duct, there is subsequent distension and inflammation, with purulent material filling the gallbladder.
TREATMENT
• Cholecystectomy or possible dissolution therapy/lithotripsy if unfit for surgery.
• ERCP for common bile duct calculi: sphincterotomy with basket or balloon removal of the stone.
• Empyema can be drained percutaneously under ultrasound control.
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Fig. Typical appearances of opaque gallbladder calculi on plain films
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Fig. Ultrasound of the gallbladder demonstrating a large single calculus. Note the acoustic shadow posterior to the gallstone.
COMMON BILE DUCT STRICTURE
Fig. Transhepatic cholangiogram: tight stricture from pancreatic carcinoma (arrow) causing severe biliary obstruction.
Common bile duct narrowing is caused by numerous disorders resulting in biliary tract obstruction. The presenting features may be jaundice, fever and rigors (Charcot’s triad).
RADIOLOGICAL FEATURES
• Ultrasound is the initial investigation of choice in a patient with jaundice. This may demonstrate a dilated common bile duct down to the level of the stricture.
• ERCP will show abnormalities of the upper gastrointestinal tract and the pancreas, in addition to the common bile duct stricture.
• Transhepatic cholangiography may be required if ERCP is unsuccessful.
CAUSES
Carcinoma of pancreas; chronic pancreatitis; postoperative; cholangiocar-cinoma
LIVER ABSCESS
A liver abscess is a localized collection of pus, which commonly results from cholangitis secondary to biliary tract obstruction. It may also follow suppurative inflammation in the drainage area of the portal vein in portal pyaemia. The latter may arise from inflammatory bowel disease, diverticulitis, appendicitis or a perforated viscus.
RADIOLOGICAL FEATURES
Ultrasound may show a single or multiple cavitating lesions. Abscesses are more common in the right lobe and on CT appear as low-density lesions, often showing peripheral ring-like enhancement after intravenous contrast. Occasionally, gas is seen centrally in the liver lesion, making the diagnosis of abscess certain. Hepatomegaly, elevation of the right diaphragm, pleural effusion and lower-lobe atelectasis may all be associated.
TREATMENT
• Antibiotics.
• Percutaneous drainage: abscesses can be drained under CT, ultrasound or fluoroscopic control.
Surgical drainage.
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Fig. Liver abscess: CT scans demonstrating a large low density lesion in the liver and after percutaneous insertion of drains (arrows).
. LIVER METASTASES
The liver is the most common organ as a site of secondary deposits. The most frequent neoplasms to metastasize to liver are those of colon, stomach, pancreas, breast and lung. Secondary deposits are much more common than primary liver tumours.
PRESENTATION
• Asymptomatic.
• Hepatomegaly.
• Ascites.
• Weight loss.
• Abnormal liver enzymes and jaundice.
• Pre-operative check prior to surgery for primary carcinoma.
• Follow-up of primary carcinoma.
RADIOLOGICAL INVESTIGATION
• Plain films.
• Ultrasound.
• CT/MRI.
• Arteriography.
• Percutaneous biopsy (guided by ultrasound or CT).
RADIOLOGICAL FEATURES
• Plain films are usually not contributory. They may show hepatomegaly and occasionally calcified liver metastases.
• Ultrasound has a high degree of accuracy, and in a good quality study, is a very sensitive examination for the detection of metastases. The normal liver has a smooth outline with a homogeneous echo pattern. The essential feature of ultrasound is to demonstrate an abnormal echo pattern in the liver, metastases often being echo-poor, cystic, hyperechoic or diffusely infiltrative.
• CT and MRI are equally precise at detecting secondary deposits.
• Arteriography is only utilized in equivocal or difficult cases. Metastases are usually avascular but renal, melanoma, carcinoid and choriocarcinoma deposits tend to be vascular. Chemotherapy or embolization may be undertaken directly via the hepatic artery.
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DIFFERENTIAL DIAGNOSIS
Haemangioma (common); hepatoma; abscess; haematoma.
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Fig. CT scan of the liver demonstrating multiple well-defined metastases of different densities
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Fig. Ultrasound of the liver; low and high echo metastases.
ACUTE PANCREATITIS
Acute pancreatitis, an inflammatory condition of the pancreas has many aetiologies, but gallstones and alcohol abuse account for the vast majority. Mumps, certain drugs, surgical trauma and pancreatic carcinoma are some of the precipitating causes. Pancreatic function and morphology usually return to normal after an acute attack.
RADIOLOGICAL FEATURES
A plain chest X-ray often reveals pleural effusions (high amylase content); these are more common on the left side. An abdominal film may show gallstones, absence of gas in the abdomen (gasless abdomen) or an ileus. A ‘sentinel loop of bowel’ may be seen in the peripancreatic region. Gut distension obscures detail on ultrasound examination but the following may be visualized: an enlarged pancreas with dilatation of the pancreatic duct; gallstones; formation of pseudocysts; abscess; dilatation of common bile duct.
When an ultrasound examination is inadequate, CT is accurate in delineating the enlarged oedematous pancreas and its complications such as necrosis, haemorrhage and fluid collections. Contrast enhancement helps the surgeon by indicating the remaining viable organ. Serial CT follows the evolution of the inflammatory process.
COMPLICATIONS
· Pleural effusions and basal atelectasis.
· Necrotizing pancreatitis: proteolytic destruction of pancreatic parenchyma, with necrosis of the pancreas and surrounding fat, resulting in a solid inflammatory pancreatic mass called a ‘phlegmon‘. A high mortality rate is to be expected when this complication arises.
· Pancreatic ascites: due to perforation of the pancreatic duct.
· Jaundice from compression of the lower end of the common bile duct by the oedematous pancreas or by common bile duct calculi.
· Abscess: occurs after an acute attack, when a collection of necrotic pancreatic tissuet>ecomes infected.
· Pseudocyst formation: results from escape of pancreatic secretions from the pancreatic duct or exudation from the surface of the inflamed pancreas; the lesser sac is the commonest location.
· Hypocalcaemia.
· Hyperglycaemia.
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Fig. CT scan of a normal pancreas
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Fig. Acute pancreatitis: CT scan showing inflammatory exudate surrounding the pancreas
Fig. CT scan showing a well-defined, low-density, pseudocyst (arrows).
CHRONIC PANCREATITIS
Chronic pancreatitis is most commonly caused by alcohol abuse.The basic pathology is ductal stenosis and obstruction resulting in atrophy and fibrosis of the pancreas; irreversible damage to the pancreas results in abnormal pancreatic’ morphology. Gallstones are frequently associated with chronic pancreatitis.
PRESENTATION
Intermittent abdominal pain; weight loss; diarrhoea; steatorrhoea; jaundice; diabetes;
RADIOLOGICAL FEATURES
• Pancreatic calcification on abdominal X-ray or CT is virtually pathognomonic of chronic pancreatitis. Calcification is noted in approximately 50%, CT being more accurate in its detection, than a plain abdominal X-ray. Almost all calcification is intraductal, and it may be either diffusely spread or localized to a specific region.
• Ultrasound and CT may show a small, irregular atrophic pancreas with altered parenchymal pattern. Ascites may be associated.
• ERCP with cannulation and injection of contrast into the pancreatic duct may show an irregular dilated duct with stenoses, obstruction and non-filling of the side branches. Pseudocysts may fill if they communicate.
• MRI shows loss of signal intensity onTI sequence.
COMPLICATIONS
• Jaundice from bile duct obstruction.
• Pseudocyst formation.
• Splenic, portal or mesenteric vein thrombosis.
• Malabsorption.
TREATMENT
• Medical: correcting diabetes and malabsorption by diet, insulin and pancreatic supplements.
• Surgical: cholecystectomy for gallstones; intervention for complications such as biliary obstruction or pseudocyst formation; partial or total pancreatectomy with drainage procedure of pancreatic duct. Cysts may be drained into the stomach under radiological guidance.
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Fig. Pancreatic calcification on a plain upper abdominal film.
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Fig. CT scan: pancreatic calcification (arrows).
PANCREATIC CARCINOMA
Pancreatic carcinoma is the fourth commonest malignant tumour after lung, colon and breast tumours. The most frequent pathological type arises from the pancreatic duct epithelium (adenocarcinoma). Tumours of the body and tail tend to be larger at the time of presentation. There is a very poor 5 year survival rate. Islet cell tumours such as insulinoma and glucagonoma are much less common and less aggressive.
PRESENTATION
Clinical symptoms usually occur late and at the time of presentation there is often local invasion of blood vessels or bowel. Only a small percentage of patients have the tumour confined to the pancreas, though peri-ampullary cancers may be localized.
• Abdominal pain, sometimes severe and continuous.
• Weight loss, anorexia.
• Obstructive jaundice.
• Malabsorption, diarrhoea.
• Diabetes.
RADIOLOGICAL FEATURES
• Ultrasound may demonstrate pancreatic and bile duct dilatation, a distended gallbladder, focal pancreatic enlargement with a hypo-echoic mass, liver metastases or ascites.
• CT will show similar findings and it may be more precise. CT may demonstrate local invasion into the retroperitoneal structures and metastases to the porta hepatis or the liver. A definitive diagnosis can often be obtained by a fine-needle or tru-cut biopsy of the mass.
• MRI: reduced signal from the pancreas onTI sequence.
• ERCP is useful when ultrasound and CT are equivocal and may show an irregular ductal obstruction or vessel encasement.
• Arteriography is sometimes utilized to define the vascular anatomy prior to surgery.
TREATMENT
Local extension beyond the confines of the organ, invasion of adjacent structures such as stomach, and secondary deposits in the liver or ascites, usually render the tumour inoperable; only 10-15% are suitable for attempted curative resection; palliative surgical procedures for relief of jaundice; stenting via ERCP, or if this is not possible then percutaneous insertion; pancreaticoduodenectomy (Whipple’s operation) for small periampullary lesions.
Fig. CT scan showing an upper abdominal mass: pancreatic carcinoma.
Fig. Pancreatic biopsy under CT control. The biopsy needle has been inserted directly through the anterior abdominal wall (arrow).
ASCITES
Ascites refers to an accumulation of fluid within the abdominal cavity: in the supine position it collects in the most dependent parts, the pelvis and paracolic gutters.
• Haemorrhagic ascites: this suggests malignant involvement of peritoneum, though it may represent haemorrhage after trauma or liver biopsy.
• Chylous ascites: chyle may rarely accumulate in the peritoneal cavity. Causes include congenital lymphangiectasia, abdominal trauma including surgery with damage to abdominal lymphatic channels, malignant infiltration, filariasis and tuberculosis.
RADIOLOGICAL FEATURES
• Plain abdomen films may show generalized haziness of the abdomen, with loss of psoas outlines. Any gas containing small bowel loops float centrally.
• Ultrasound localizes fluid collections in the abdomen with considerable accuracy.The fluid appears anechoic, is freely mobile and bowel loops may be seen floating in the fluid. It can be aspirated, under ultrasound control, for a diagnostic tap or percutaneous drainage by means of a catheter can be undertaken.
• CT demonstrates ascites as a low-density margin around the intraabdominal organs and is most clearly seen adjacent to the liver.
CAUSES
Transudate. Freely mobile, simple fluid collection.
• Cirrhosis.
• Hypoproteinaemia.
• Renal failure.
• Pericarditis.
• Cardiac failure.
• Budd-Chiari syndrome.
Exudate. Complex fluid collection and may contain solid tissue or inflammatory debris.
• Primary or secondary carcinoma.
• Tuberculous peritonitis.
• Pancreatitis.
• Meig’s syndrome.
Fig. Ascites: abdominal CT visualizing ascites as low density surrounding the liver and spleen.
Fig. Ascites: ultrasound examination demonstrates the free intraabdominal collection (black) surrounding the liver and gallbladder.
SUBPHRENIC ABSCESS
A subphrenic abscess is a fluid collection between the diaphragm and the liver or spleen. It is a recognized complication of upper abdominal surgery but may occur as a result of perforation of the gastrointestinal tract. The abscess occurs more commonly on the right.
PRESENTATION
• Upper abdominal pain; shoulder pain; pyrexia (swinging).
RADIOLOGICAL INVESTIGATIONS
• Plain abdomen or chest film.
• Ultrasound.
• CT.
• Isotope scanning
RADIOLOGICAL FEATURES
• Plain chest films may feature a pleural effusion or basal collapse and consolidation. An elevated diaphragm on the affected side and a gas or fluid level under the diaphragm are diagnostic features.
• Ultrasound and CT will demonstrate the volume and extent of the collection.
• Isotope scanning with Indium-labelled white cells, shows increased activity at the site of the abscess, but is rarely necessary for diagnosis.
TREATMENT
• Percutaneous drainage either under ultrasound or CT guidance.
• Surgical drainage.
OTHER SITES OF ABDOMINAL ABSCESS FORMATION
• Psoas abscess: commonly tuberculous but may be pyogenic.
• Pancreatic abscess: follows acute pancreatitis.
• Renal/perinephric abscess: often haematogenous spread or secondary to renal obstruction; diabetics are particularly susceptible.
• Pelvic abscess: results in diarrhoea due to rectal irritation and inflammation.
• Liver abscess: pyogenic or amoebic.
• Appendix abscess: perforation of the appendix may lead to a localized abscess. An abdominal X-ray may show a calcified appendicolith.
• Pericolic abscess: particularly from diverticular disease.
• Intra-abdominal abscess: secondary to bowel perforation.
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Fig. Air/fluid level below the right diaphragm in subphrenic abscess.
Fig. Ultrasound reveals the abscess with multiple septations between the diaphragm and liver.
