Biliary Atresia

Biliary atresia (BA) accounts for the majority of chronic liver diseases without a genetic cause, and is the most common cause of liver transplantation in children. Although BA is an idiopathic disease, most cases are thought to be secondary to viral, metabolic, or vascular insults in susceptible individuals. Girls are more affected than boys, and a worldwide incidence of 1:14,000 has been reported for this condition (Sokol et al. 2003; Hinds et al. 2004).

BA can be viewed as two different entities, the embryonic and the postnatal form. Approximately 10%-35% of patients will be afflicted by cholestasis from the first hours of life, and the association of this cholestasis with different congenital malformations in these patients will constitute the embryonic or fetal form. On the other hand, a gradual increase in bilirubin levels with a clinically evident jaundice after the sixth week of life will characterize the postnatal form. Acholic stools and hepatomegaly are other common manifestations (Suchy 2003; Rosenthal 1999).

Antenatally, US is a useful tool for detection of biliary malformations. The presence of a cystic structure localized at the hepatic hilum can occur in BA or may present as a choledochal cyst. However, if this cyst is small and anechoic it will be more suggestive of an atresia of the biliary canals, while the presence of an echoic cyst that gradually increases in size supports a choledochal cyst. The specificity of these US findings with BA, however, is not well known (Kim et al. 2000).

Postnatally, the parenchymal pattern of the liver in a patient with BA may be normal or slightly heterogeneous on US examination. The vast majority of patients will have a small gallbladder with a length less than 1.5 cm or an absent gallbladder. Absence of the gallbladder is therefore highly suspicious of BA, while a normal size gallbladder or a change in its size after feeding will support neonatal hepatitis (Teele and Share 1991; Kanegawa et al. 2003; Kirks and Griscom 1998). Some studies have reported the presence of fibrous tissue close to the porta hepatis, and US may depict this tissue as a triangular or tubular echogenic structure. Although a positive predictive value of 95%, and a sensitivity between 84%-93% has been noted between this "triangular cord" and BA, inflammatory diseases and cirrhosis can mask this finding (Gubernick et al. 2000; Jaw et al. 1999; Norton 2002; Mowat et al. 1976) (Fig. 4.2a,b).

Other congenital anomalies such as polysplenia, midline liver, interrupted inferior vena cava, situs inversus, preduodenal portal vein, and intestinal malrotation will support the diagnosis of heterotaxy syndrome (Sokol et al. 2003; Kim et al. 2000).

A 99Tc-IDA derivate isotope scan (scintigraphy) can also differentiate between BA and neonatal hepatitis. Phenobarbital must be administered for 3-5 days to jump-start hepatocellular function. If the tracer reaches the duodenum, biliary atresia can be excluded. However, some authors recommend imaging at 24 h to exclude delayed excretion. Scintigraphy has 50%-75% specificity and 90%-100% sensitivity for BA (Petersen and Ure 2003) (Fig. 4.2c,d).

MRCP using T2-weighted turbo spin echo sequences has been helpful in the diagnosis and visualization of choledochal cysts and dilated common bile ducts. However, in neonates and young infants the intrahepatic ducts are very thin and their visualization can be challenging. The triangular cord sign may be seen on MRCP as a high signal intensity area on T2-weighted images along the portal tract, and this corresponds to inflammatory tissue and fluid (Kim et al. 2000; Jaw et al. 1999).

Finally, an intraoperative cholangiogram will finally depict the anatomy of the biliary ducts and will assess whether the main right and left hepatic ducts have the caliber necessary to perform the Kasai hepatic portoenterostomy (Gazelle et al. 1998) (Fig. 4.2e).

A percutaneous liver biopsy will clinch the diagnosis. Histological analysis will show bile plugs, lymphocytic infiltration in the portal tracts and proliferation of the small intrahepatic bile ducts. There may also be an absence of the extrahepatic biliary ducts and the presence of periportal fibro-sis, which will progress to cirrhosis. The accuracy of this procedure is reported to be greater than 90% (Gubernick et al. 2000).

Surgical success depends on several factors, such as the time of operation, extent of fibrosis, and jaundice disappearance. Surgical timing of the Kasai procedure is one of the most important factors, showing a 17% success rate when the surgery is done after 90 days of age, and 91% success rate if it is done before 60 days of age. Disappearance of jaundice after surgery has been correlated with survival rates of between 73%-92% after 10 years; however, if the jaundice continues, the 3-year survival can be as low as 20% (Sokol et al. 2003).

In general, after surgery, one third of patients will require liver transplantation in the first year of life; another third by their teenage years and the remaining third will have a good outcome.

Fig. 4.2a-e. Biliary atresia (BA). a Slightly inhomogeneous echo texture of the liver, prominent wall of common bile duct (CBD) (arrows). b Tiny gallbladder. c,d Tracer uptake in liver, both kidneys, and bladder, but not in a gallbladder or duodenum. e Transhepatic cholangiography reveals atretic CBD (arrow)

Fig. 4.2a-e. Biliary atresia (BA). a Slightly inhomogeneous echo texture of the liver, prominent wall of common bile duct (CBD) (arrows). b Tiny gallbladder. c,d Tracer uptake in liver, both kidneys, and bladder, but not in a gallbladder or duodenum. e Transhepatic cholangiography reveals atretic CBD (arrow)

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