Dilatation of the bile duct in the left lobe of the liver is a manifestation in imaging, and the causes of dilatation of the bile duct in the left outer lobe of the liver include: congenital bile duct dilatation, biliary obstruction, and inflammatory stimulation. 1. Congenital bile duct dilatation: most of them develop in infancy and early childhood, and are related to factors such as heredity and abnormal proliferation of bile duct epithelium. 2. Biliary obstruction: bile duct stones, stenosis, tumors and other diseases can cause bile ducts to be blocked, resulting in obstruction of bile discharge, bile ducts are enlarged due to high pressure in the bile ducts, which is manifested as dilatation in imaging examination. 3. Inflammatory stimulation: Biliary tract infection, liver abscess and other diseases will lead to bacteria in the bile, and the bacterial infection will stimulate the bile ducts to thicken and dilate. There may be other causes of bile duct dilatation in the left lobe of the liver, such as viral infection, pregnancy, cholecystectomy, etc. It is recommended to go to the hospital in time to improve the examination and clarify the cause of the disease.