Biliary duct dilatation is a congenital malformation of the bile ducts, which can be seen as cystic dilatation of the intrahepatic or extrahepatic bile ducts, and is a relatively rare disease. It is a relatively uncommon disease that occurs in females, commonly in children and adolescents, and less commonly in adults. The classification is still based on Todani’s opinion in 1977, which divided bile duct cysts into 6 types. Todani’s bile duct cyst typology: Type I: common type: (1) narrowly defined common bile duct cysts; (2) segmental common bile duct dilatation: diffuse spindle dilatation. Type II: extrahepatic bile duct diverticulum. Type III: terminal cyst of the common bile duct. Type IV-Type A: multiple cysts of intrahepatic and extrahepatic bile ducts. Type IV-Type B: extrahepatic bile duct multiple cysts. Type V: intrahepatic bile duct solitary or multiple cysts with hepatic fibrosis (Carolis disease). Type VI: bile duct cysts.