Bile duct dilatation, also known as bile duct cyst, is a relatively rare primary bile duct lesion that can be perpetuated by congenital bile duct dilatation in infancy or develop in adulthood, mainly manifesting as single or multiple localized dilatation of intra- and extrahepatic bile ducts. The incidence of this disease accounts for approximately 1% of benign biliary tract diseases. The incidence of bile duct dilatation is significantly higher in Japan and Southeast Asian countries (1/1000) than in Europe and the United States (1/150,000 to 1/100,000), and the incidence in women is 3 to 4 times higher than that in men, mostly in infancy and childhood, and about 20% in adulthood. With the popularity of abdominal ultrasound and imaging examinations such as CT and MRI, 10% to 36% of diagnosed patients are asymptomatic patients, and the diagnosis rate of bile duct dilatation has increased significantly. Congenital dysplasia of the bile duct wall and terminal stenosis or atresia of the bile duct are the basic factors for the occurrence of this disease, and the possible causes are: 1. genetic factors; 2. congenital abnormalities of pancreaticobiliary coarctation; 3. congenital dysplasia of the bile duct. The typical clinical presentation is a triad of abdominal pain, abdominal mass and jaundice. The abdominal pain is in the right upper abdomen and can be a persistent dull pain; the abdominal mass is located in the right upper abdomen, under the rib cage, and often changes in volume and size; during the period of infection, pain, and jaundice, the mass increases, and after the symptoms are relieved the mass can be slightly reduced; jaundice is intermittent and is often the main symptom in young children, and the depth of jaundice is directly related to the degree of biliary obstruction. When combined with infection, jaundice may continue to deepen, abdominal pain may worsen, the mass may be painful to the touch, and there may be chills and fever. Clinical manifestations of biliary cirrhosis and portal hypertension may also occur in the late stage. In addition to the corresponding clinical manifestations, the diagnosis of bile duct dilatation also requires imaging and laboratory findings, which provide the basis for patient condition assessment, treatment plan development and surgical modality selection. The main points of diagnosis include the extent of bile duct involvement, the degree of dilatation, and complications. Once the disease is diagnosed, surgery should be performed as soon as possible, otherwise it may lead to serious complications such as cirrhosis, carcinoma or cyst rupture due to episodes of cholangitis.