Congenital bile duct dilatation can occur in any part of the intrahepatic and extrahepatic bile ducts, and is more common in Eastern countries, especially in Japan. The ratio of male to female is about 1:3-4. Symptoms can appear in early childhood, and about 80% of cases develop in childhood. The possible causes are: 1. congenital abnormalities of pancreaticobiliary duct cohesion: the embryonic common bile duct and the end of the pancreatic duct are not separated, or the common bile duct enters the pancreatic duct at a right angle, or the pancreatic duct merges into the bile duct above the pot belly, and the pancreatic fluid easily flows back into the bile duct, causing damage to the lining of the bile duct and fibrous changes, resulting in cystic dilatation of the common bile duct; 2. congenital biliary dysplasia: during the embryonic period, the primitive bile duct proliferates into cords, and then later vacuolates through, such as excessive vacuolation of the bile duct epithelium can lead to weakness of the bile duct wall and cystic dilatation; 3, genetic factors: the incidence of this disease is significantly higher in women than in men, and some believe that it is related to sex chromosomes. According to the site, extent and morphology of bile duct dilatation, it can be divided into five types Type I: cystic dilatation. It accounts for about 90% of cases and can involve all or part of the common hepatic duct and common bile duct. The bile ducts are spherically or gourd-shaped dilated, with a maximum diameter of 25 cm and severe narrowing of the distal bile ducts at the dilated part. The bile cyst ducts generally merge into the cyst, and the left and right hepatic ducts and intrahepatic bile ducts are normal. Type II: diverticulum-like dilatation. The lateral dilatation of the common bile duct wall is diverticulosis-like expansion, which is rare clinically. Type III: cystic prolapse at the opening of the common bile duct. A limited cystic dilatation near the opening of the duodenum at the end of the common bile duct, which prolapses into the lumen of the duodenum and often causes partial obstruction of the bile duct. Type IV: dilated intra- and extrahepatic bile ducts. The intrahepatic bile ducts have multiple cystic dilatations of varying sizes, and the extrahepatic bile ducts are also cystically dilated. Type V: Intrahepatic bile duct dilatation (Caroli disease). Multiple cystic dilatation of the intrahepatic bile ducts with hepatic fibrosis and no dilatation of the extrahepatic bile ducts. Common hazards: 1. Carcinoma. The cancer rate is 10% and close to 20% in adults; 2, ulcers; 3, gallstone formation; 4, biliary cirrhosis; 5, cyst rupture hemorrhage and biliary peritonitis; 6, portal hypertension; 7, infection. Typical manifestations: 1, abdominal pain. It is located in the right upper abdomen and can be persistent dull pain; 2, abdominal mass. more than 80% of patients can have a cystic mass with smooth surface in the right upper abdomen; 3, jaundice. Ancillary tests: ultrasound, PTC (percutaneous transhepatic cholangiography), ERCP (endoscopic retrograde cholangiopancreatography), MRCP (magnetic resonance cholangiopancreatography), radionuclide scan. Treatment: The main treatment is complete resection of the cyst and Roux-en-Y anastomosis of the bile and intestine. In case of severe infection or perforation, the cyst can be drained by cystostomy first, and then the cyst can be resected and bile-intestinal Roux-en-Y anastomosis can be performed after the general condition improves and the jaundice subsides; for those with limited intrahepatic bile duct dilatation, resection of the diseased liver segment can be performed at the same time; if the intrahepatic bile duct dilatation ( Caroli’s disease) or complications of cirrhosis, liver transplantation can be considered.