Choledochal cyst (type IV)

Choledochal cysts are congenital conditions associated with benign cystic dilatation of bile ducts. They are uncommon in western countries but not as rare in East Asian nations like Japan and China.

They were classified into 5 types by Todani in 1977.
Classification was based on site of the cyst or dilatation.
 Type I: Most common variety involving sacular or fusiform dilatation of a portion or entire common bile duct (CBD) with normal intrahepatic duct.
 Type II: Isolated diverticulum protruding from the CBD.
 Type III or Choledochocele: Arise from dilatation of duodenal portion of CBD or where pancreatic duct meets.
 Type IV: Dilatation of both intrahepatic and extrahepatic biliary duct.
 Type V or Caroli's disease: Cystic dilatation of intra hepatic biliary ducts.