Biliary Atresia

Biliary atresia is a congenital obstruction of the intra- and/or extrahepatic ducts, usually presenting with neonatal jaundice. The overall incidence is approximately 1 in 15,000 births, but it is far more common in the Asian population.

The most common finding on US (seen in almost two-thirds of neonates with biliary atresia) is an absent, small (< 1.5 cm), or empty gallbladder in a neonate who has been fasting for several hours ( Fig. 9.9 a). Furthermore, a triangular or tube-shaped echogenic focus with a thickness of 4 mm or more that follows the portal veins can be seen at the porta hepatis ( Fig. 9.9 b). This so-called triangular cord sign has a reported sensitivity of 62 to 93% and a specificity of 96 to 100%, but can be difficult to distinguish from periportal echogenicity due to inflammation or cirrhosis. Other signs that suggest the presence of biliary atresia include an absent common bile duct, a hypertrophic hepatic artery ( Fig. 9.9 b,c), and increased hepatic subcapsular flow on color Doppler US ( Fig. 9.9 d).

Choledochal Cysts

Choledochal cysts are rare congenital saccular or fusiform dilatations of the biliary tree with an incidence of approximately 1 to 2 in 100,000 to 150,000 live births. Again, they are far more common in the Asian population, with a reported prevalence of 1 in 1,000 persons in Japan. Choledochal cysts are usually classified according to Todani into five subtypes ( Fig. 9.10 ). Type I cysts, the most common, occur in up to 80 to 90% of all cases ( Fig. 9.11 and Fig. 9.12 ). They are often associated with an abnormal junction of the common bile duct with the pancreatic duct. Frequent complications include ascending cholangitis and/or pancreatitis, liver cirrhosis, portal hypertension, and spontaneous cyst rupture. There is an increased risk for developing cholangiocarcinoma, especially after the age of 10 years. In cases of delayed presentation, these cysts can become extremely large ( Fig. 9.13 ).

With US, the location and degree of bile duct dilatation can be easily depicted. Sludge or bile stones can be identified by bile stasis in the dilated ducts. In type V choledochal cysts (Caroli disease), the kidneys should be examined as well because this type is often associated with autosomal-recessive polycystic kidney disease ( Fig. 9.14 ). Pathognomonic for Caroli disease is the so-called central dot sign ( Fig. 9.15 ), which is the result of fibrovascular bundles, consisting of portal vein and hepatic artery branches, crossing the dilated choledochal cysts. Although originally described on CT, this sign is well visualized on US.

The differentiation of a choledochal cyst ( Fig. 9.16 a–c) from a simple hepatic cyst, hepatic abscess, or pancreatic pseudocyst is sometimes difficult. Additional imaging consists of either endoscopic retrograde cholangiopancreatography (ERCP), which can be performed only in specialized centers by well-trained gastroenterologists and allows intervention, and/or magnetic resonance cholangiopancreatography (MRCP), which can be performed on all modern MR scanners, although sedation may be necessary ( Fig. 9.16 d, e; Video 9.16).

Congenital Portosystemic Shunts

Congenital portosystemic shunts are rare congenital anomalies that are mostly detected on US. The children can present with abnormal liver tests, elevated blood ammonia, and/or serum bile acid levels, or the shunt can be found incidentally on US. A portosystemic shunt can be intrahepatic ( Fig. 9.17 ), in which case there is a connection between a portal vein and either a hepatic vein or the inferior caval vein, or extrahepatic, in which case the portal trunk or a branch of it is in direct contact with the inferior caval vein. Extrahepatic portosystemic shunts are classified according to Abernethy. Type I consists of an atretic portal vein with the splenic and superior mesenteric veins terminating either separately in the inferior vena cava (type Ia) or as a common venous trunk (type Ib; Fig. 9.18 ). In Abernethy type II, there is a normal or hypoplastic portal vein with partial shunting into the inferior vena cava.

Intrahepatic portosystemic shunts can regress spontaneously before the age of 2 years, but if they persist, intervention may be needed. Long-term consequences of these shunts are the development of liver tumors (see later section on focal nodular hyperplasia), hepatic encephalopathy, hepatopulmonary syndrome, and pulmonary hypertension.

Hepatitis

Hepatitis is an inflammation of the liver. The most common cause is viral infection, but hepatitis can also be a result of autoimmune disease, metabolic disorders, or drug use. In the acute phase, imaging plays no significant role other than to rule out other diseases. The role of imaging is the follow-up of patients with hepatitis, in which case the interest lies in the detection of cirrhosis, portal hypertension, and tumors (especially hepatocellular carcinoma after hepatitis caused by hepatitis B virus or hepatitis C virus; Fig. 9.19 ).

Pyogenic Abscess

Although relatively rare in the Western world, pyogenic liver abscesses are the most frequent abscesses encountered in children. The most common pathogen is Escherichia coli ( Fig. 9.20 and Fig. 9.21 ; Video 9.21). There is a well-known relation between appendicitis and the formation of liver abscesses; however, with the improved detection of appendicitis, this cause is decreasing. The most common pathways of infection are through the biliary tract and the portal system. Also, penetrating trauma can be the cause of abscess formation ( Fig. 9.22 ).

On US, a liver abscess usually appears as a rounded or ovoid hypoechoic lesion, but it can have a heterogeneous appearance, as well. The wall may be thick and irregular. Septa and debris can be encountered. Less commonly, pyogenic microabscesses are encountered ( Fig. 9.23 ). Although not pathognomonic, a diffuse pattern is seen in Staphylococcus aureus infection, and a clustered pattern is seen in E. coli infection.

Fungal Infections

Fungal hepatic infections are characterized by the presence of numerous microabscesses (often also present in the spleen). They are encountered in children with hematologic malignancies or a compromised immunologic system. The most common causative agent is Candida albicans ( Fig. 9.24 ). On US, four patterns have been described: wheel within wheel, bull’s-eye, uniformly hypoechoic, and focally echogenic.

Parasitic Infections

The most common parasitic infection of the liver is due to Entamoeba histolytica, and infection of the liver is actually the most common extraintestinal presentation of this infection. US does not discriminate between a pyogenic abscess and an Entamoeba abscess. However, on aspiration of the abscess, the typical chocolate-colored pus can be encountered.

Hydatid or echinococcal cysts are caused by infection with Echinococcus granulosus, which is endemic around the Mediterranean but can also be encountered in areas where sheep are bred. On US, a purely cystic lesion may be seen, but often daughter cysts and/or calcification of the cyst wall is encountered. A pathognomonic finding is the so-called water lily sign, which is seen if the endocyst becomes detached from the outer pericyst ( Fig. 9.25 ).

Cholecystitis

Cholecystitis is relatively rare in young children, but it becomes more common with increasing age when related to cholelithiasis. Acalculous cholecystitis also occurs, but usually only in critically ill children after trauma, major surgery, or burns, or during sepsis. On US, the gallbladder is typically enlarged and tender, with thickening of the wall. Pericholecystic fluid may be seen, and gallstones may be present ( Fig. 9.26 ). Cholecystitis should be distinguished from hydrops of the gallbladder. In the latter, the distended gallbladder lacks wall thickening, and patients are usually not as ill as in cholecystitis. Isolated gallbladder wall thickening without other signs of cholecystitis does occur in children with ascites and hepatitis/cholangitis.

Infectious Cholangitis

Infectious cholangitis occurs in children and usually has a bacterial origin, although viral, fungal, and parasitic infections are also possible, especially in the immune-compromised host. Infectious cholangitis is often associated with congenital or immune-related bile duct abnormalities, surgically corrected biliary atresia (Kasai procedure; Fig. 9.27 and Fig. 9.28 ), liver transplant, and certain immunodeficiency states. Therefore, the primary goal of US when infectious cholangitis is suspected is to search for anatomical abnormalities and/or obstruction of the biliary tract.

Chole(docho)lithiasis

Gallstones are relatively uncommon in children, with a reported prevalence of up to 1.9%. They are more frequently detected in asymptomatic children because of the more widespread use of US. Chole(docho)lithiasis may be idiopathic ( Fig. 9.29 ), but in neonates and young infants it is often associated with sepsis, the use of diuretics, or total parenteral nutrition. In older children, gallstone formation may be related to obesity (an increasing problem in the pediatric age group; Fig. 9.30 ), sickle cell disease ( Fig. 9.31 ), hemolytic anemia, cystic fibrosis ( Fig. 9.32 ), and disease of the small bowel.

On US, gallstones will appear as echogenic foci with or without acoustic shadowing ( Fig. 9.33 and Fig. 9.34 ). Gallstones are calcified in approximately 50% of cases, particularly if associated with a hemolytic disorder. When located in the gallbladder, they often change in position with gravity. In the biliary tree, gallstones may cause biliary dilatation due to obstruction, which in most cases can be easily visualized on US ( Fig. 9.35 and Fig. 9.36 ). The differentiation of biliary sludge from small, nonshadowing gallstones may be difficult ( Fig. 9.37 ).

In children treated with ceftriaxone, pseudochole(docho)lithiasis, as a result of biliary precipitation, can be encountered. In these children, follow-up US, after the discontinuation of treatment, will show resolution of the pseudochole(docho)lithiasis ( Fig. 9.38 ).

In cases of symptomatic chole(docho)lithiasis, the surgical technique of choice is laparoscopic cholecystectomy. With this new surgical technique, new complications are encountered, the most important of which is damage to the biliary tree. There are four different types of injury, which can be classified as follows:

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   Type A: leakage of the cystic duct or peripheral intrahepatic biliary tract;

   
   
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   Type B: leakage from the common bile duct without the presence of a stricture;

   
   
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   Type C: stricture of the common bile duct without leakage;

   
   
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   Type D: complete transsection of the common bile duct with or without resection of a section of the common bile duct ( Fig. 9.39 ).

   

In these postsurgical patients, US should be used to detect intraperitoneal fluid collections, especially around the liver hilum, and dilatation of the biliary tree.