Histological investigations into the difference between cystic and fusiform types of congenital biliary dilatation.

We investigated the histological differences in the common bile duct wall of bile ducts with congenital biliary dilatation, examining 10 cystic types and 11 fusiform types. A flattened mucosa was found in the cystic type, and a tufted mucosa was occasionally found in the fusiform type. Glands in the choledochus wall were less common in the cystic type than in the fusiform type. Smooth muscle fibre was more abundant in the cystic type than in the fusiform type, and it was markedly developed in the distal choledochus in the cystic type. Based on these results we suggest that the developmental difference of smooth muscle fibres in the distal choledochus in the embryonic period may be closely related to the morphological difference between the cystic and fusiform types of congenital biliary dilatation.