The most common cause of common biliary duct dilatation is obstruction due to gallstones, states the Radiology Assistant. Another cause of obstruction besides gallstones is stricture, or narrowing, of the common bile duct.
Strictures of the bile duct may be due to tumors, such as cholangiocarcinoma, gallbladder adenocarcinoma or pancreatic adenocarcinoma, or metastatic disease. Strictures may also result from inflammation from pancreatitis, radiation or chemotherapy, biliary parasites, AIDS cholangiopathy or primary sclerosing cholangitis, according to the Radiology Assistant.
If there are no gallstones and no strictures causing obstruction, the cause of the bile duct dilatation may be non-obstructive biliary disease, notes the Radiology Assistant. Examples of non-obstructive biliary diseases are Caroli disease, choledochal cyst, recurrent pyogenic cholangitis and primary sclerosing cholangitis.
Caroli disease is a genetically inherited disease that results in dilatation of the ducts within the liver, according to the Radiology Assistant. It is associated with polycystic kidney disease. Choledochal cyst is a dilatation of the bile ducts outside the liver that is present at birth. Recurrent pyogenic cholangitis is common in Asian countries and is associated with biliary parasites. Primary sclerosing cholangitis results in strictures in the bile ducts and is associated with ulcerative colitis and Crohn's disease.