Solution: Choledochal cysts are congenital anomalies of the bile ducts. They consist of cystic dilatations of the extrahepatic biliary tree, intrahepatic biliary radicles, or both. The majority present before the age of 10, but they can present in adulthood. They are divided into 5 types based upon which portion of the biliary tree is involved. The vast majority of patients with choledochal cysts have an anomalous junction of the common bile duct with the pancreatic duct with entry of the pancreatic duct into the common bile duct 1 cm or more proximal to where the common bile duct reaches the ampulla of Vater. This condition allows pancreatic secretions and enzymes to reflux into the common bile duct and ultimately results in inflammation and weakening of the bile duct wall. Complications include: pancreatitis, cholangitis, hepatocellular inflammation and damage, a cholangiocarcinoma (9-28%). Because of this possibility, the treatment is surgical. The five types of choledochal cysts as defined on emedicine.com are: * Type I choledochal cysts - These are the most common, representing 80-90% of the lesions. Type I cysts are dilatations of the entire common hepatic and common bile ducts or of segments of each. They can be saccular or fusiform in configuration. Type I cysts can be divided into 3 subclassifications, including type IA cysts, which are typically saccular and involve all or a major portion of the extrahepatic bile duct (common hepatic duct plus common bile duct). * Type II choledochal cysts - These are relatively isolated protrusions or diverticula that project from the common bile duct wall. They may be either sessile or connected to the common bile duct by a narrow stalk. * Type III choledochal cysts - Also called choledochoceles, these are found in the intraduodenal portion of the common bile duct. * Type IVA cysts - These are characterized by multiple dilatations of the intrahepatic and extrahepatic biliary tree. Most frequently, a large, solitary cyst of the extrahepatic duct is accompanied by multiple cysts of the intrahepatic ducts. * Type IVB choledochal cysts - These consist of multiple dilatations that involve only the extrahepatic bile duct. * Type V choledochal cysts - These are defined by dilatation of the intrahepatic biliary radicles. Often, numerous cysts are present with interposed strictures that predispose the patient to intrahepatic stone formation, obstruction, and cholangitis. The cysts are typically found in both hepatic lobes. Occasionally, unilobar disease is found and most frequently involves the left lobe.