Pancreaticobiliary ductal union. The main pancreatic duct and the common bile duct open into the second part of the duodenum alone or after joining as a common channel. A common channel of greater than 15 mm (an anomalous pancreaticobiliary duct) is associated with congenital cystic dilatation of the common bile duct and carcinoma of the gall bladder. Even a long common channel (greater than or equal to 8 mm) is associated with a higher frequency of carcinoma of the gall bladder. Gall stones smaller than the common channel and a long common channel predispose to gall stone induced acute pancreatitis. Separate openings for the two ductal systems predisposes to development of gall stones and alcohol induced chronic pancreatitis. The role of ductal union has also been investigated in primary sclerosing cholangitis and biliary atresia. 