Cystic Changes in the Liver and Biliary Tree
A choledochal cyst is a dilatation of the common bile duct that presents with neonatal jaundice (Fig. 4.3). They are more frequent in females and in the Asian population with a worldwide frequency of 1:15,000. Many theories regarding the etiology of choledochal cysts have been proposed (Gazelle et al. 1998). In the neonate a congenital etiology has been proposed, while in older children it is thought to be secondary to a pancreatobiliary obstruction that will produce an increased intraductal pressure and a reflux of the activated pancreatic enzymes into the common bile duct. Other possible etiologies include a deficient autonomic innervation with few ganglion cells in the distal common bile duct, a retrovirus infection, and an immune or familial cause.
There are five types of choledochal cysts (Fig. 4.4a):
• Type I: Dilatation of the common bile duct, which may be cystic, focal, or fusiform (subtypes A, B and C, respectively).
• Type II: Saccular diverticulum of the common bile duct.
• Type III: Cystic dilatation of the intramural portion of the common bile duct and is contended by some to represent a duodenal diverticulum rather than a choledochal cyst.
• Type IV-A: Intrahepatic and extrahepatic dilatation of the biliary tree.
• Type IV-B: Multiple extrahepatic cysts
• Type V: Multiple intrahepatic biliary dilatations, synonymous with Caroli disease
Type V cyst is a rare congenital disease characterized by segmental-saccular ductal dilatation. Recurrent bacterial cholangitis and stone formation have been associated with "Caroli disease" (Fig. 4.4b,c) (Todani et al. 2003).
On US a choledochal cyst will be seen as a cystic lesion with a thin wall, well defined borders, and echogenic material inside the cyst that corresponds to biliary sludge. However, it is important in the US evaluation to determine if the cyst is really a dilated choledochus, if the intrahepatic ducts are compromised, and if there is portal hypertension. As US has shown a specificity of 97% for choledochal cysts, it is widely used as the first diagnostic tool (Gubernick et al. 2000; Teele and Share 1991).
Endoscopic retrograde cholangiopancreatography (ERCP) is an excellent tool that affords good visualization of the biliary ducts, and the extent of the choledochal cyst. However, in pediatric patients, and especially in the very young, it can be a challenging procedure, with an unsuccessful outcome in 5%-30% of all patients.
CT might also play an important role. It allows for good characterization of intrahepatic cysts, the distal part of the common bile duct, and the head of the pancreas, and in post-surgical patients it gives a very accurate evaluation of the biliary-enteric anastomosis. However, cholangiography can dem-
onstrate the biliary ducts as well, or better, than CT, with less radiation exposure but with a morbidity and sedation risk (Kühn et al. 2004).
In some instances neither US nor CT can determine whether the cyst has communication with the biliary tract. Scintigraphy with 99tc at 30 min, 6 h, and 24 h could then be used. The sensitivity of the examination may be as high as 100% for type I cysts or as low as 66% for type IV cysts. However, scintigraphy will not delineate the intrahepatic compromise by choledochal cysts (Lam et al. 1999).
Magnetic resonance cholangiography (MRCP) T2-weighted sequences provide an evaluation of the intra- and extrahepatic bile ducts. Other sequences such as a T1 post-contrast injection provide fine detail on the periportal spaces, parenchyma, and blood vessels. Visualization of the entire biliary tree and the choledochal cysts using MRCP has been reported (Krause et al. 2002). MRCP provides information for the operative planning with less potential risks than ERCP or percutaneous transcutaneous cannulation (PTC).
Although CT-cholangiography can depict intra-hepatic stones and the pancreatic duct better than MRCP, CT radiation exposure and potential contrast reactions have limited CT use (Mowat et al. 1976).
Cyst excision and hepaticoenterostomy is the definitive treatment of the disease, and will reduce the 20-fold risk of biliary carcinoma with choledochal cyst. Infants with choledochal cyst may present with the classic triad of jaundice, pain, and right upper quadrant mass; however, this is true only in 15%-20% of cases. Usually, only one of the triad will be present. Ascites, liver dysfunction, and coagulop-athy may be found in some patients with progressive disease and without treatment (Behrman et al. 2004).
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