Imaging of the choledochal cyst.

Choledochal cysts are rare and usually manifest in infancy and childhood. They are considered congenital because they occur in fetuses and neonates. Their origin may be related to an abnormal connection between the pancreatic duct and common bile duct and chronic reflux of pancreatic juice into the bile duct, resulting in irritation of the duct and subsequent dilatation. Choledochal cysts appear as cystic or fusiform dilatation of the common bile duct at radiography. Ultrasonography is the best initial method of evaluating dilatation of the intra- and extrahepatic bile ducts. Computed tomography is considered to be more accurate in delineating the intrahepatic biliary tree. Hepatobiliary scintigraphy with technetium-99m disofenin provides physiologic information on hepatic uptake and accumulation of radionuclide in the dilated biliary tree. Endoscopic retrograde cholangiopancreatography, percutaneous transhepatic cholangiography, and intraoperative cholangiography are definitive studies that demonstrate anatomic details of the biliary tree and the pancreaticobiliary ductal junction.