The ultrastructural changes of the common bile duct following reflux of pancreatic juice in a canine model

Pancreatic juice refluxing into the common bile duct (CBD) through an anomalous pancreaticobiliary ductal union has been regarded as one of the etiology in forming a choledochal cyst. However, the actual morphological changes of the CBD and hence the pathogenesis have not been demonstrated. A canine model in which continuous reflux of pancreatic juice into the bile duct was created by pancreaticocholedochostomy (PCS) were performed in 24 mongrel adult dogs. Twenty one dogs after PCS showed dilatation of CBD (diameter 7 to 15 mm, normal 2.2 ± 0.8 mm) when they were sacrificed at 1, 2, 4, 8, 16 and 32 weeks respectively. The size of CBD reached maximally at 2 weeks after PCS, and remained the same at 32 weeks. The ultrastructure of the dilated CBD when examined under electron microscope showed mucosal sloughing, 'splitting' of the intercellular junctional structures, basement membrane degeneration and rupture, submucosal vessel occlusion with ischemic necrosis, bile pigment deposition and fragmentation of the deep muscle layer. All these changes in the CBD suggested chemical destructive processes. We concluded that the bile-pancreatic juice mixture is harmful to the common bile duct and may cause limit degree of dilatation.