Choledochal cyst - type I

Last revised by Khalid Alhusseiny on 4 Mar 2024

Type I choledochal cysts appear as a fusiform or cystic dilatation of the extrahepatic biliary system (common bile duct +/- common hepatic duct).

Although uncommon in Western countries (1:100,000 to 1:150,000), they are the most common type of biliary cyst. Their prevalence may be higher in East Asian countries.

They are 3-4x more common in women 4.

Patient may present with abdominal pain, jaundice, or a palpable abdominal mass.

The origin of these cysts is still not entirely clear, but current theories suggest that they may arise from a combination of altered pancreaticobiliary junction (APBJ) anatomy and/or reflux of pancreatic exocrine secretions with subsequent weakening of bile duct walls.

The designation "type I" arises from the Todani classification. Some believe that the division between type I and type IV cysts is arbitrary 2.

Some have also modified the type I classification to include three subtypes:

  • Ia: dilatation of extrahepatic bile duct (entire)

  • Ib: dilatation of extrahepatic bile duct (focal segment)

  • Ic: dilatation of the common bile duct portion of the extrahepatic bile duct

The subclassification is controversial, with some suggesting no need for subclassification and others suggesting that it may have prognostic benefit (e.g. type Ia may predispose to anastomotic stricture) 5.

Diagnosis of a type I choledochal cyst requires ruling out dilatation of the extrahepatic biliary system from a filling defect (e.g. choledocholithiasis) or obstructing malignancy.

  • cystic or fusiform dilatation of the common duct (common bile duct +/- common hepatic duct)

  • distinct from gallbladder

  • cystic or fusiform dilatation of the common bile duct

  • distal common bile duct may be easier to visualize than on ultrasound

  • cystic or fusiform dilatation of the common bile duct

  • MRCP considered best non-invasive imaging study for evaluation of the biliary system

There is a reported risk of malignancy in type I choledochal cysts ranging from 2.5-28%.

Treatment entails removal of the dilated portion of the bile duct and reconnection of the biliary system, usually requiring a hepaticojejunostomy. Rarely, reconstruction above the confluence of the left and right hepatic ducts is necessary.

Cyst drainage procedures or an anastomotic connection from the cyst to the stomach, duodenum, or jejunum tend to be problematic and have largely been abandoned 3.

Biliary duct cysts were described by Vater in 1723 6.

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