Choledochal Cysts

Choledochal cysts, also known as biliary cysts, are rare congenital abnormalities involving cystic dilations in the biliary tree. Choledochal cysts are classified based on their anatomical location, morphology, and may be associated with abnormal pancreaticobiliary junctions (APBJ). Type I cysts are the most common and may appear as anechoic cystic lesions communicating with the biliary tree. Type I cysts fall into 3 subtypes. In type IA, a fusiform dilatation of the common bile duct (CBD) gives rise directly to the gallbladder and may involve the common hepatic duct or extrahepatic segments of the right or left hepatic duct. Type IB is a diverticulumlike cystic dilatation of the distal CBD which does not give rise to the gallbladder and is not associated with an APBJ. Type IC is characterized by a smooth and diffuse dilatation of the CBD. Type II cysts involve the dilatation of the extrahepatic bile ducts proximal to the insertion of the cystic duct. These are also known as bile duct diverticula. Type III cysts are l ocated within the duodenal wall at the pancreaticobiliary junction and also known as choledochoceles. Type IV cysts consist of multiple dilatations of the intrahepatic bile ducts; subtype IVA involves both intrahepatic ducts and CBD whereas subtype IVB affects only the CBD. Type V cysts have intrahepatic saccular or fusiform dilatation without obstruction and are also known as Caroli disease. Choledochal cysts likely result from abnormal biliary tree development during embryogenesis. APBJs may also be implicated due to reflux of pancreatic juice into the CBD. Other factors may include weak bile duct walls, distal biliary obstruction, or sphincter of Oddi dysfunction.