3: Ultrasound of the Gallbladder and Biliary Tree

Pitfalls in Scanning the Gallbladder

If you still cannot find it, ensure the scanner frequency and settings are optimized, find the porta hepatis, and scan just below it in the transverse section. This is the area of the gallbladder fossa, and you should see at least the anterior gallbladder wall if the gallbladder is present (Fig. 3.4).

A contracted, stone-filled gallbladder, producing heavy shadowing, can be difficult to identify because of the lack of any contrasting fluid in the lumen.

True agenesis of the gallbladder is rare.

Duodenum mimicking gallbladder pathologic conditions:

• The close proximity of the duodenum to the posterior gallbladder wall often causes it to invaginate the gallbladder. Maximize your machine settings to visualize the posterior gallbladder wall separate from the duodenum and turn the patient to cause the duodenal contents to move.

Other segments of the fluid-containing gastrointestinal tract can also cause confusion (Fig. 3.5).

Stones that do not shadow:

• This is likely to be because of poor settings, rather than any lack of stone reflectivity.
• Ensure they are stones and not polyps by positioning the patient erect and watching them move with gravity (beware – polyps on long stalks also move around).
• The stones may be smaller than the beamwidth, making the shadow difficult to display.
• Ensure the focal zone is set at the back of the gallbladder.
• Increase the line density, if possible, by reducing the field of view.
• Scan with the highest possible frequency to ensure the narrowest beamwidth.
• Reduce the TGC and/or power to ensure you have not saturated the echoes distal to the gallbladder.

Beware of the folded gallbladder! If the gallbladder is folded and the fundus lies underneath the bowel, you may miss pathologic conditions. Always try to unfold it by positioning the patient. A fold in the gallbladder may mimic a septum. Septations are comparatively rare and have been overreported in the past because of the presence of folding.

Pathology or Artifact?

Bile Duct Measurements

Tip box

Patients post cholecystectomy who have had previous duct dilatation frequently also have a persistently dilated but non-obstructed duct (Fig. 3.8). Be suspicious of a diameter of 10 mm or more as this is associated with obstruction because of the formation of stones in the duct.

By knowing which of these two types of bilirubin is present in the jaundiced patient, the clinician can narrow the diagnostic possibilities. The ultrasound then further refines the diagnosis (Fig. 3.10).

Jaundice can fall into one of two categories:

• Obstructive (sometimes called posthepatic) – in which the bile is prevented from draining out of the liver because of obstruction to the biliary duct(s).
• Non-obstructive (prehepatic or hepatic) – in which the elevated bilirubin level is because of hemolysis (the breakdown of the red blood cells) or a disturbance in the mechanism of the liver for uptake and storage of bilirubin, such as in inflammatory or metabolic liver diseases.

Abnormal Liver Function Tests

Ultrasound Appearances

There are three classic acoustic properties associated with stones in the gallbladder; they are highly reflective, mobile, and cast a distal acoustic shadow. In most cases, all these properties are demonstrated (Figs. 3.11–3.13).

Mobility

Most stones are gravity-dependent, and this may be demonstrated by scanning the patient in an erect position (Fig. 3.12) when a mobile calculus will drop from the neck or body of the gallbladder to lie in the fundus. However, some stones will float, forming a reflective layer just beneath the anterior gallbladder wall with shadowing that obscures the rest of the lumen (Fig. 3.13B). When the gallbladder lumen is contracted, either because of physiological or pathological reasons, any stones present are unable to move, and this is also the case in a gallbladder packed with stones (Fig. 3.17D).

Occasionally a stone may become impacted in the neck, and movement of the patient is unable to dislodge it. Stones lodged in the gallbladder neck or cystic duct may result in a permanently contracted gallbladder, a gallbladder full of fine echoes because of inspissated (thickened) bile (Fig. 3.18), or a distended gallbladder because of a mucocele (see below).

Biliary Reflux and Gallstone Pancreatitis

Bile reflux is also associated with anomalous cystic duct insertion (Fig. 3.22A, B), which is more readily recognized on MRCP than ultrasound.

Further Management of Gallstones

MRCP and endoscopic retrograde cholangiopancreatography (ERCP) demonstrate stones in the duct with greater accuracy than ultrasound, particularly at the lower end of the CBD, which may be obscured by duodenal gas on ultrasound (Fig. 3.22C, D).⁵ ERCP is invasive, carrying a small risk of morbidity or rarely mortality because of perforation, infection, or pancreatitis but has the advantage of providing the therapeutic option of sphincterotomy and stone removal. This is the modality of choice when stones are known to exist in the duct (for example, following MRCP) and has supplanted surgical removal in many cases.⁶

Laparoscopic cholecystectomy is the preferred method of treatment for symptomatic gallbladder disease in an elective setting. Acute cholecystitis is also increasingly managed by early laparoscopic surgery, with a slightly higher rate of conversion to open surgery than elective cases.⁷ Laparoscopic ultrasound may be used as a suitable alternative to operative cholangiography to examine the common duct for residual stones during surgery.⁸ It compares well to cholangiography, with a sensitivity and specificity of 96% and 100%, and avoids any radiation dose, but has been slow to be adopted in the United Kingdom, as it requires specialized equipment and training.⁹ Both ultrasound and cholescintigraphy are used in monitoring postoperative biliary leaks or hematoma (Fig. 3.23).

Other less common options include dissolution therapy and extracorporeal shock wave lithotripsy. However, these treatments are often only partially successful, require careful patient selection, and also run a significant risk of stone recurrence.¹⁰

Mucocele of the Gallbladder

If the gallbladder is dilated in the absence of duct dilatation, do a careful search for an obstructing lesion at the neck; a stone in the cystic duct is more difficult to identify on ultrasound as it is not surrounded by echo-free bile (Fig. 3.18).

Mirizzi’s Syndrome

On ultrasound, the gallbladder is typically contracted and contains debris. A stone impacted at the neck may be demonstrated together with dilatation of the intrahepatic ducts with a normal caliber lower common duct (Fig. 3.24). The diagnosis is difficult, as it is frequently impossible to rule out carcinoma. Computed tomography (CT) or magnetic resonance imaging (MRI) may assist in this distinction, and ERCP is still considered the “gold standard” especially as it can offer therapeutic stone removal and/or stent placement.¹² Endoscopic or intraductal ultrasounds, if available, have improved the diagnostic accuracy of suspected cases.¹³ Although rare, it is an important diagnosis as cholecystectomy in these cases has a higher rate of operative and postoperative complications.¹⁴

The most likely cause of a contracted gallbladder is physiological, following a meal. (This may still occur despite instructions to fast, and it is always worth enquiring when and what the patient has last eaten or drunk.) The normal gallbladder wall is thickened when contracted, and this must not be confused with a pathological process (Fig. 3.25).

Pathological Causes of a Small Gallbladder

The reflective surface of the stones and distal shadowing are apparent, and the anterior gallbladder wall can be demonstrated with correct focusing and good technique (Figs. 3.17D, 3.26). Do not confuse the appearances of a previous cholecystectomy when bowel in the gallbladder fossa casts a shadow for a contracted stone-filled gallbladder.

A less common cause of a small gallbladder is the microgallbladder associated with cystic fibrosis (Fig. 3.27). The gallbladder itself is abnormally small, rather than just contracted. Cystic fibrosis also carries an increased incidence of gallstones because of the altered composition of the bile and bile stasis, and the wall might be thickened and fibrosed from cholecystitis.

Porcelain Gallbladder

When the gallbladder wall becomes calcified, the resulting appearance is of a solid reflective structure, causing a distal shadow in the gallbladder fossa (Fig. 3.28). (This can be distinguished from a gallbladder full of stones where the wall can usually be seen anterior to the shadowing [Fig. 3.17D].)

A porcelain gallbladder probably results from a gallbladder mucocele – a long-standing obstruction of the cystic duct, usually from a stone. The bile inside the non-functioning gallbladder is gradually replaced by watery fluid. The wall becomes fibrotic and thickened, and ultimately calcifies.

There is an association between porcelain gallbladder and gallbladder carcinoma; therefore, a prophylactic cholecystectomy is usually performed to preempt malignant development.¹⁵

Shadowing from the calcified anterior gallbladder wall can obscure the gallbladder contents and can mimic bowel in the gallbladder fossa. A plain X-ray also clearly demonstrates the porcelain gallbladder.

Polyps

Gallbladder polyps are common, usually asymptomatic lesions which are incidental findings in up to 5% of the population. Occasionally they are the cause of biliary colic. They are reflective structures projecting into the gallbladder lumen, which do not cast an acoustic shadow. Unless on a long stalk, they will remain fixed on varying the patient position and are therefore usually distinguishable from stones (Fig. 3.30).

Several types of polyps exist, the most common being cholesterol polyps, which account for around 60% of gallbladder polyps. Others are adenomyomatosis and inflammatory polyps, both of which are also usually benign. True adenomas are less common. There is an association between larger adenomatous gallbladder polyps (> 10 mm) and subsequent carcinoma, especially in patients over 50 years of age. Therefore, the finding of a solitary polyp poses a diagnostic dilemma, and cholecystectomy is often advised (Fig. 3.30D, E). Endoscopic ultrasound (EUS) may provide further information in such cases,²⁰ as it provides high-resolution images of tiny polyps and the layers of the gallbladder wall, and there is some evidence that there is a correlation between EUS appearances and gallbladder polyp histology. Generally, gallbladders in asymptomatic patients with polyps of > 1 cm should undergo rescanning to identify subsequent polyp growth and increased risk of carcinoma, and many clinicians advocate cholecystectomy to preempt malignant transformation.²¹ In particular, gallbladder polyps in patients with primary sclerosing cholangitis (PSC) have a much greater likelihood of malignancy (40%–60%).²² Smaller polyps of less than 1 cm in diameter may also be safely monitored with ultrasound.²³

There is some evidence to suggest that ultrasound contrast agents are useful in demonstrating tumor vascularity in potentially malignant polyps, such as adenomatous polyps.²⁴ However, so far, this technique has proved non-specific, as some benign cholesterol polyps also demonstrate increased vascularity (Fig. 3.30F, G).

Algorithms are being developed for guidance on the management of gallbladder polyps, with collaboration with primary care, hepatobiliary surgeons, and radiology departments. You should make yourself aware of your local departmental policies and guidelines on the management of gallbladder polyps.

Other guidelines also consider the risk factors that the patient may have included being > 50 years old, if they have other conditions such as PSC, and if the patient is of Indian ethnicity. Factors such as sessile (broad-based) polyps are also considered a risk factor (Diagram 3.1). These factors, polyp size and whether the patient is symptomatic then develop a pathway of surgery or surveillance, with small stable polyps only followed up for a maximum of five years. Due to the variations in guidance, it is important that departments develop local protocols to ensure continuity.

Cholesterolosis

Also known as the “strawberry gallbladder,” this gets its name because of the multiple tiny nodules on the surface of the gallbladder mucosal lining. These nodules result from a buildup of lipids in the gallbladder wall and are often not visible on ultrasound. However, in some cases, multiple polyps also form on the inner surface, projecting into the lumen, which are clearly visible on ultrasound (Fig. 3.31). Cholesterolosis may be asymptomatic or may be accompanied by stones and consequently require surgery to alleviate symptoms of biliary colic. The finding of multiple gallbladder polyps should trigger ultrasound follow-up in the asymptomatic patient (see above).

Patients with a long-standing history of chronic cholecystitis may experience (sometimes repeated) attacks of acute inflammation. The gallbladder wall is thickened, as for chronic inflammation, and may become focally thickened with both hypo- and hyperechoic regions. Stones are usually present (Fig. 3.37).

Gangrenous Cholecystitis

In a small percentage of patients, acute gallbladder inflammation progresses to gangrenous cholecystitis. Areas of necrosis develop within the gallbladder wall. The wall itself may bleed, and small abscesses form (Fig. 3.38). This severe complication of the inflammatory process requires immediate cholecystectomy.

The gallbladder wall is friable and may rupture, causing a pericholecystic collection and possibly peritonitis. Inflammatory spread may be seen in the adjacent liver tissue as a hypoechoic, ill-defined area. Loops of the adjacent bowel may become adherent to the necrotic wall, forming a cholecystoenteric fistula. This condition is rare but tends to be associated with older patients, often with a background of diabetes or cardiovascular disease, and carries increased morbidity and mortality.³¹

The wall is asymmetrically thickened, and areas of abscess formation may be demonstrated. The damaged inner mucosa sloughs off, forming the appearance of membranes in the gallbladder lumen. The gallbladder frequently contains infected debris. The presence of a bile leak may also be demonstrated with hepatobiliary scintigraphy, using technetium^99M, which is useful in identifying a bile collection that may otherwise be obscured by bowel on ultrasound.

Emphysematous Cholecystitis

This is a form of acute gangrenous cholecystitis in which the inflamed gallbladder may become infected, particularly in diabetic patients with gas-forming organisms. Both the lumen and the wall of the gallbladder may contain air, which is highly reflective, but which casts a “noisy,” less definite shadow than that from stones. Discrete gas bubbles have been reported on ultrasound within the gallbladder wall32 and may also extend into the intrahepatic biliary ducts.³³ The air rises to the anterior part of the gallbladder, obscuring the features behind it (Fig. 3.39). This effect may mimic air-filled bowel on ultrasound.

Emphysematous cholecystitis has traditionally had a much higher mortality rate than other forms of cholecystitis, requiring immediate cholecystectomy. However, improvements in ultrasound resolution and the early clinical recognition of this condition suggest that it is now being diagnosed earlier and may be managed more conservatively. The gas in the gallbladder may be confirmed on a plain X-ray (Fig. 3.40), but ultrasound is more sensitive in demonstrating the earlier stages.

Gallbladder Empyema

Empyema is a complication of cholecystitis in which the gallbladder becomes infected behind an obstructed cystic duct. Fine echoes caused by pus are present in the bile (Fig. 3.41). These patients may initially present with the usual features of acute cholecystitis but may then progress to become very ill with fever and acute pain. Localized perforation of the gallbladder wall may cause leakage of infected bile to form a pericholecystic gallbladder collection with subsequent peritonitis. Ultrasound may be used to guide bedside drainage (Fig. 3.41D–F) to allow the patient’s symptoms to settle before surgery is attempted.³⁴

Assessment of the Level of Obstruction

It is possible for the sonographer to work out where the obstructing lesion is situated by observing which parts of the biliary tree are dilated (Fig. 3.42):

• • Dilatation of the CBD (i.e., that portion of the duct below the cystic duct insertion) implies obstruction at its lower end.
• • Dilatation of both biliary and pancreatic ducts implies obstruction distally at the head of the pancreas or ampulla of Vater. This is more likely to be because of carcinoma of the head of the pancreas, ampulla, or acute pancreatitis than a stone. However, it is possible for a stone to be lodged just distal to the confluence of the biliary and pancreatic ducts.
• • Dilatation of the gallbladder alone (i.e., without ductal dilatation) is usually caused by obstruction at the neck or cystic duct (Fig. 3.18).

To assess whether the gallbladder is pathologically dilated may be difficult on ultrasound. The dilated gallbladder will have a rounded, bulging shape because of the increase in pressure inside it.

A gallbladder whose wall has become fibrosed from chronic cholecystitis because of stones will often lose the ability to distend so that the biliary ducts can look grossly dilated despite the gallbladder remaining “normal” in size or contracted.

Early Ductal Obstruction

Beware of very early common duct obstruction before the duct becomes obviously dilated, the duct may be mildly dilated at the lower end, just proximal to a stone, but normal in its intrahepatic portion. Likewise, intermittent obstruction by a small stone at the lower end of the duct may be non-dilated when the scan is performed (Fig. 3.20).

A significant ultrasound feature in the absence of any other identifiable findings is that of thickening of the wall of the bile duct. This not only represents an inflammatory process in the duct wall, which may be found in patients with small stones in a non-dilated duct but is also associated with sclerosing cholangitis.³⁵

It is sometimes technically difficult in some patients (particularly those with diffuse liver disease) to determine whether a tubular structure on ultrasound represents a dilated duct or a blood vessel. Color Doppler will differentiate the dilated bile duct from a branch of the hepatic artery or portal vein (Fig. 3.43), provided that the vein is not thrombosed, of course.

It is not useful to use color Doppler routinely to locate the CBD; the angle of insonation is frequently perpendicular to the beam, so the vein may display no color signal, confusing the operator further. In addition, the application of color Doppler reduces the line density and image resolution – exactly the opposite of what you require when searching for a small duct.

Diagnosis and Assessment of the Cause of Obstruction

The numerous causes of biliary dilatation are summarized in Table 3.2. Frequently, ultrasound diagnoses the obstruction but does not identify the cause. This is a case for perseverance by the operator, as the lower end of the CBD is visible in most cases once the overlying duodenum has been moved away (Figs. 3.19, 3.20, 3.44). However, ultrasound is not generally regarded as a reliable tool for identifying ductal stones and is frequently unable to diagnose ductal strictures, especially those from benign causes. In the absence of a definite diagnosis of stones, MRCP is an effective, non-invasive technique in the diagnosis of CBD stones and strictures (Fig. 3.44F),⁵,³⁶ avoiding the need for the more invasive ERCP.

Although diagnostically highly accurate, the use of ERCP is usually reserved for occasions when therapeutic stone removal or stent insertion may be required, as it is an invasive procedure with attendant risks of pancreatitis, cholangitis, and rarely, perforation of the bile duct or duodenum.³⁷,³⁸ Complications occur in up to 8% of patients undergoing ERCP, with a mortality rate of up to 0.5%,³⁹ so the technique should ideally be reserved for those requiring therapeutic intervention.

EUS also has accuracy in detecting CBD stones comparable with ERCP while avoiding the risks associated with radiation and biliary instrumentation. It is not yet as readily available as ERCP and requires specialist skills and equipment with a significant learning curve.⁴⁰ CT and MRI are useful for staging purposes if the obstructing lesion is malignant. Cholangiocarcinomas spread to the lymph nodes and the liver – and small liver deposits are particularly difficult to recognize on ultrasound if the intrahepatic biliary ducts are dilated.

In hepatobiliary scintigraphy, technetium^99M-labeled derivatives of iminodiacetic acid are excreted in the bile and may help to demonstrate sites of obstruction, e.g., in the cystic duct – or abnormal accumulations of bile, e.g., choledochal cysts. The technique is also useful in demonstrating postoperative bile leaks.⁴¹

Courvoisier’s law, to which there are numerous exceptions, states that if the gallbladder is dilated in a jaundiced patient, then the cause is not because of a stone in the common duct. The reasoning behind this is that gallstones cause a degree of wall fibrosis from chronic cholecystitis, which would prevent it from distending. There are many exceptions to this “law,” which include the formation of stones in the duct, without gallbladder stones, and obstruction by a pancreatic stone at the ampulla.

• • Do not assume that obstructive jaundice in a patient with gallstones is because of a stone in the CBD. Jaundice may be attributable to other causes.
• • Do not assume that obstructive jaundice cannot be because of a stone in the CBD if the gallbladder does not contain stones. A solitary stone can be passed into the duct from the gallbladder, or stones can form within the duct.

Management of Biliary Obstruction

Laparoscopic ultrasound is a useful adjunct to the surgical exploration of the biliary tree, and its accuracy in experienced hands equals that of X-ray cholangiography. Its potential has been slow to be realized in many centers, as it requires training and has a steep learning curve. However, the lack of ionizing radiation, together with its accuracy in experienced hands, has allowed it to replace fluoroscopic cholangiography in some centers.42

EUS can also be used to examine the CBD, avoiding the need for laparoscopic exploration of the duct. It is highly accurate in diagnosing ductal stones, particularly in experienced hands⁴³ and may be more sensitive than MRCP in the detection of small ductal stones (depending on the MRCP slice thickness).⁴⁴ However, its invasive nature means it is usually reserved for cases when MRCP is negative in patients where the probability of stones or an obstructing lesion remains high.

The treatment of malignant obstruction is determined by the stage of the disease. Accurate staging is best performed using CT and/or MRI. If surgical removal of the obstructing lesion is not a suitable option because of local or distant spread or other comorbidities, palliative stenting may be performed endoscopically to relieve the obstruction and decompress the ducts (Fig. 3.45). The patency of the stent may be subsequently monitored with ultrasound by assessing the degree of duct dilatation.

Clinical suspicion of early obstruction should be raised if the serum alkaline phosphatase is elevated (often more sensitive in the early stages than a raised serum bilirubin). In the presence of ductal dilatation on ultrasound, further imaging, such as CT, MRCP, or EUS, may then refine the diagnosis.

Intrahepatic Tumors Causing Biliary Obstruction

Focal masses that cause segmental intrahepatic duct dilatation are usually intrinsic to the duct itself, e.g., cholangiocarcinoma. It is also possible for a focal intrahepatic mass, whether benign or malignant, to compress an adjacent biliary duct, causing subsequent obstruction of that segment. However, this is not a common cause of biliary dilatation and occurs most usually with hepatocellular carcinomas.45 Most liver metastases deform, rather than compress, adjacent structures, and biliary obstruction only occurs if the metastases are very large and/or invade the biliary tree. A hepatocellular carcinoma (HCC) or metastatic deposit at the porta hepatis may obstruct the common duct by squeezing it against adjacent extrahepatic structures.

Benign intrahepatic lesions rarely cause ductal dilatation, but occasionally their sheer size obstructs the biliary tree.

Choledochal Cysts

Most commonly found in children, this is associated with biliary atresia, in which the distal “blind” end of the duct dilates into a rounded, cystic mass in response to raised intrahepatic pressure. Choledochal cysts in adults are rare and tend to be asymptomatic unless associated with stones or other biliary diseases. They tend to be associated with an anomalous insertion of the CBD into the pancreatic duct, which allows pancreatic enzymes to reflux into the bile duct resulting in inflammation and weakening of the duct wall, forming a choledochal cyst (Fig. 3.46).⁴⁶

The dilatation is less common because of a non-obstructive cause in which the biliary ducts become ectatic and can form diverticula. This may be because of a focal stricture of the duct, which causes reflux and a localized enlargement of the duct proximal to the stricture (see also “Caroli’s Disease” below).

Complications of choledochal cysts include cholangitis, formation of stones, and progression of the condition to secondary biliary cirrhosis, which may be associated with portal hypertension.

It may be difficult to differentiate a choledochal cyst, particularly if solitary, from other causes of hepatic cysts. The connection between the choledochal cyst and the adjacent biliary duct may be demonstrated with careful scanning, but further imaging, including MRCP, is frequently required.

Cholangitis

Duct dilatation may be present, depending on the cause of the cholangitis. In severe cases, the duct walls appear thickened and irregular, and debris can be seen in the larger ducts (Fig. 3.47). Care should be taken to differentiate ductal wall thickening from tumor invasion, and further imaging may be necessary to exclude malignancy.

Bacterial cholangitis is the most common form because of ascending bacterial infection from the duodenum or portal vein. Bacterial cholangitis is also associated with biliary enteric anastomoses and may be complicated by abscesses if the infection is progressive and untreated. Small abscesses may be difficult to diagnose on ultrasound, as they are frequently isoechoic and ill-defined in the early stages, and biliary dilatation makes evaluation of the hepatic parenchyma notoriously difficult.

Contrast CT may identify small abscesses not visible on ultrasound, and MRCP or ERCP demonstrates mural changes in the ducts.

In patients who have had cholecystectomy associated with previous dilatation of the CBD, it is common to find a persistent (but non-significant) mild dilatation of the duct postoperatively. The serum alkaline phosphatase and bilirubin levels should be normal in the absence of a pathologic condition. Because stones may be found in the duct postoperatively, it is important to differentiate non-obstructive from truly obstructive dilatation in a symptomatic patient (Fig. 3.48A). If in doubt, the patient may be rescanned at a suitable interval to assess any increase in ductal diameter.

Fibrosis of the Duct Walls

Clinical features include jaundice, itching, and fatigue. Twenty-five percent of patients also have gallstones, complicating the diagnosis; 70% of affected patients also have ulcerative colitis. Progressive, gradual fibrosis causes strictures and eventually obliterates the biliary tree. Untreated, this leads to hepatic failure. PSC has a strong association with cholangiocarcinoma, and it is this, rather than hepatic failure, which may lead to death. In the absence of malignancy, however, hepatic transplantation has a 70%-90% five-year survival rate,47 although recurrence of the disease is a recognized complication.⁴⁸

Ultrasound appearances

The ultrasound appearances in PSC may be normal, particularly in the early stages, or may demonstrate a coarse, hyperechoic liver texture. Ductal strictures may cause downstream dilatation in some segments (Fig. 3.49), and in some cases, there is marked biliary dilatation. However, in most patients, the biliary ducts are prevented from dilatation by the surrounding fibrosis and so appear unremarkable on ultrasound. MRCP is superior at demonstrating intrahepatic ductal strictures (Fig. 3.50). Mural thickening, particularly in the CBD, may be demonstrated with careful scanning (Fig. 3.50A),⁴⁹ and may be the only ultrasound sign. Ultrasound also demonstrates the effects of portal hypertension in advanced disease. The gallbladder may also have a thickened wall and can be dilated.⁵⁰

Due to the association between PSC and cholangiocarcinoma, which may be multifocal, a careful search must be done for mass lesions. Because the ultrasound appearances may be those of a coarse, nodular liver texture, it is difficult to identify small cholangiocarcinomas. Ultrasound contrast may help to highlight suspected lesions (Fig. 3.51), but MRI is the next investigation of choice to stage the disease. The diagnosis is an important one because the patient’s prognosis and management are affected by the presence of cholangiocarcinoma. If no masses are identified, the prognosis is favorable, and patients may benefit from the endoscopic removal of stones to relieve symptoms, endoscopic stenting of main duct strictures to relieve jaundice, and subsequent liver transplantation to preempt the formation of carcinoma. However, if carcinoma is already present, five-year survival falls to 10%.

Primary Biliary Cirrhosis (PBC)

PBC is another example of a cholestatic disease that gradually obliterates the biliary tree and ultimately leads to cirrhosis. It is discussed more fully in Chapter 2.

Caroli’s Disease (Congenital Intrahepatic Biliary Dilatation)

This is a rare, congenital condition where the bile ducts are irregularly dilated with diverticula-like projections. These diverticula may become infected and may separate off from the biliary duct, forming choledochal cysts (Fig. 3.52). In most cases, the entire hepatobiliary system is affected to some degree. Sufferers may present in early childhood, with symptoms of portal hypertension,⁵¹ or may remain well until adulthood, presenting with cholangitis. It is generally thought to be an autosomal recessive, inherited condition, and the prognosis is poor. Medical control of associated portal hypertension with varices can improve the quality of life.

In a few cases, the disease is confined to one or two segments of the liver, in which case a cure can be effected with hepatic resection.⁵² The extrahepatic biliary tree is often unaffected.

The ultrasound appearances are usually widespread intrahepatic duct dilatation, with saccular and fusiform biliary ectasia. The diagnosis is often unclear because it is also associated with biliary stone formation. The dilatation is also associated with cholangitis, and signs of infection may be present in the form of debris within the ducts or even abscesses. Sometimes frank choledochal cysts can be located.

Advanced disease is associated with portal hypertension and, in some cases, cholangiocarcinoma.⁵³ The presence of multiple cystic spaces on imaging must not be confused with multi- or polycystic disease, and the identification of communication between the cysts and the biliary tree with CT or MRI is an important factor in making the diagnosis.⁵⁴

Parasites

Parasitic organisms, such as the Ascaris worm and liver fluke, are extremely rare in the United Kingdom. However, they are a common cause of biliary colic in Africa, the Far East, and South America. Hyperechoic linear structures in the gallbladder lumen or dilated ducts should raise the sonographer’s suspicion in patients native to or those who have visited these countries.55 Impacted worms in the biliary ducts may also mimic other ductal masses, and they are a rare cause of obstructive biliary dilatation (Fig. 3.53).

Patients may present with acute cholangitis or abdominal pain and vomiting. Endoscopic management is frequently highly effective.⁵⁶

Fine echoes in the bile within the gallbladder are not uncommon on an ultrasound scan. This is common because of the inspissation of bile following prolonged starvation – for example, following surgery (Fig. 3.54). These appearances disappear after a normal diet is resumed, and the gallbladder has emptied and refilled. Echogenic bile occurs when the solutes in the bile precipitate, often because of hypomotility of the gallbladder, and can commonly be seen following bone marrow transplantation and in patients who have undergone prolonged periods (4–6 weeks) of total parenteral nutrition.⁵⁷

Prolonged biliary stasis may lead to inflammation and/or infection, particularly in postoperative patients and those in immunosuppression. Its clinical course varies from complete resolution to progression to gallstones. However, following the resumption of oral feeding, the gallbladder may contract and empty the sludge into the biliary tree causing biliary colic, acute pancreatitis, and/or acute cholecystitis.⁵⁸ For this reason, cholecystectomy may be considered in symptomatic patients with biliary sludge.

The fine echoes may form a gravity-dependent layer and may clump together, forming “sludge” balls (Fig. 3.54B). To avoid misdiagnosing sludge balls as polyps, turn the patient to disperse the echoes or rescan after the patient has resumed a normal diet.

Biliary stasis is associated with an increased risk of stone formation.⁵⁹ Occasionally, echogenic bile persists even with normal gallbladder function (Fig. 3.55). It is likely that there is a spectrum of biliary disease in which gallbladder dysmotility and subsequent saturation of the bile leads to the formation of crystals in the bile and also in the gallbladder wall. Some particles become quite large, forming microlithiasis, which is likely to be an intermediate stage in stone formation.⁶⁰ Pain and biliary colic may be present prior to stone formation. Biliary crystals or “microlithiasis” (usually calcium bilirubinate granules) have a strong association with acute pancreatitis,⁶¹ and their presence in patients who do not have gallstones may therefore be highly significant.

Obstructive Causes of Biliary Stasis

Bile stasis within the ducts occurs either because of prolonged and/or repetitive obstruction or a cholestatic disease such as PBC (Chapter 2) or PSC. This can lead to cholangitis.

Haemobilia

The appearances depend upon the stage of evolution of the bleeding. Fresh blood appears as fine, low-level echoes. Blood clots appear as solid, non-shadowing structures, and there may be hyperechoic, linear strands.62 A history of trauma may allow the sonographer to differentiate haemobilia from other causes of echogenic bile, particularly those associated with gallbladder inflammation, and there may be other evidence of abdominal trauma on ultrasound – such as a hemoperitoneum.

Pneumobilia

It is characterized by highly reflective linear echoes (Fig. 3.56), which follow the course of the biliary ducts. The air usually casts a shadow that is different from that of stones – often having reverberative artifacts and being much less well-defined or clear. This shadowing obscures the lumen of the duct and can make an evaluation of the hepatic parenchyma difficult.

Pneumobilia may also be present in emphysematous cholecystitis, an uncommon complication of cholecystitis, in which gas-forming bacteria are present in the gallbladder (see above) or in cases where a necrotic gallbladder has formed a cholecystoenteric fistula. Rarely, multiple biliary stones form within the ducts throughout the liver, which can be confused with the appearance of air in the ducts.

Management of the Patient with Cholangiocarcinoma

Surgical resection of the tumor is becoming more successful in patients with single lesions,65 and liver transplantation in patients with PSC has a good prognosis, provided the tumor bulk is low. Palliation is frequently the only feasible option, and the insertion of a stent, either percutaneously or endoscopically, to bypass the obstructing lesion and assist drainage of the liver will relieve the symptoms and often allows the patient to return home for some months.

Other treatment options, such as chemotherapy, have limited success. Despite improvements in treatment, only a minority of patients survive beyond 12 months after the initial diagnosis.⁶⁶