Todani classification of bile duct cysts - Type I: dilation of the extrahepatic bile duct. Type II: a bile duct diverticulum. Type III: a choledochocele: focally dilated, intramural segment of the distal common bile duct into the duodenum. Type IVa: dilation of the entire EHBD duct with extension to IHBD bile ducts. type 4b: multiple cystic dilations involving only the EHBD. Type V: Also known as Caroli disease which is cystic dilations of IHBD.