Cholangiocarcinoma: pictorial essay of CT and cholangiographic findings.

Cholangiocarcinomas that involve areas from the peripheral intrahepatic duct to the distal common duct have similar morphologic features, and traditional classification schemes based on the location of the involved ducts sometimes overlap. Nevertheless, cholangiocarcinoma is usually classified as either intrahepatic or extrahepatic, and intrahepatic cholangiocarcinoma is further classified as either peripheral or hilar. However, the distinction between peripheral intrahepatic cholangiocarcinoma and hilar cholangiocarcinoma is largely based on the site of origin. Therefore, in some tumors that arise peripheral to the secondary bifurcation of one of the hepatic ducts, clear differentiation between the two types of cholangiocarcinoma is not always possible. In addition, the distinction between hilar cholangiocarcinoma and extrahepatic cholangiocarcinoma is not clearly defined. The different biologic behaviors of the tumors seem to be caused by their varying locations and their size at the time of diagnosis. Further molecular or biochemical investigation is needed to support the "field theory," which states that all cholangiocarcinomas are biologically the same tumor originating from the same biliary epithelium.