Choledochal cysts

Choledochal cysts are rare (<1%)congenital conditions associated with benign cystic dilatation of bile ducts (>20mm). They consist of cystic dilatations of the extrahepatic biliary tree, intrahepatic biliary radicles, or both. (no /mild peripheral intrahepatic bile duct dilatation).


Presentation 
Most of them present in 1st year of life; adult presentation is rare and usually at this stage is associated with complication . Classic triad of intermittent abdominal pain, jaundice, and a right upper quadrant abdominal mass is found only in minority of patients.

• They were classified into 5 types by Todani in 1977.

• Classification was based on site of the cyst or dilatation. 

Type I choledochal cyst

• 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.

•  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 cyst

• 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 cyst

• Also called choledochoceles.

• These are found in the intraduodenal portion of the common bile duct. 

Type IV (A) choledochal cyst

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.

CT scan demonstrating intrahepatic biliary duct dilatation in a type IV choledochal cyst.

ERCP demonstrating extrahepatic and intrahepatic biliary duct dilatation in a type IV choledochal cyst.

Type V choledochal cyst (Caroli disease)

• 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 and most frequently involves the left lobe.

Pathophysiology

• Most likely multifactorial.

• Some aspects of the disease are consistent with a congenital etiology, others with a congenital predisposition to acquiring the disease.

• The vast majority,more than 90% have an anomalous junction of the common bile duct with the pancreatic duct (anomalous pancreatobiliary junction [APBJ]).

•  An APBJ is characterized by the 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 (10-58%).

• In some CBD drains into pancreatic duct.

This shows the normal relationship between the common bile and pancreatic ducts as they join and pass through the wall of the duodenum (left) and the abnormal relationship (right) in which there is a common channel that permits destructive digestive pancreatic enzymes to enter and damage the common bile duct.
A.). B.) This dye injection of the bile and pancreas ducts shows the typical picture of an abnormal pancreaticobiliary duct junction in association with a choledochal cyst (arrow).

• The APBJ allows pancreatic secretions and enzymes to reflux into the common bile duct.

• In the relatively alkaline conditions found in the common bile duct, pancreatic proenzymes can become activated. 

• This results in inflammation and weakening of the bile duct wall.

From a congenital standpoint,

• defects in epithelialization and recanalization of the developing bile ducts during organogenesis and congenital weakness of the duct wall.