Dilatation of the extrahepatic bile ducts means that the width of the extrahepatic bile ducts exceeds the range of normal values. It is usually caused by congenital, bile duct obstruction and so on. 1. Congenital: Congenital cystic dilatation of the common bile duct is a congenital malformation disease of the biliary tract. Some patients have no symptoms as children and develop symptoms only after they grow up. Some patients also have abdominal pain and jaundice caused by extrahepatic bile duct dilatation when they are young. 2. Bile duct obstruction: such as sclerosing cholangitis, malignant tumor of gallbladder duct compressing the common hepatic duct, choledocholithiasis, bile duct tumor, duodenal papillary tumor and pancreatic head carcinoma, etc., all of which may lead to obstruction of the bile duct and extrahepatic bile duct dilatation. There are many causes of extrahepatic bile duct dilatation, and patients are advised to go to the hospital in time to avoid delaying the condition and causing adverse consequences.