The “complex type” classification of PBM is rare, [1] and in particular, PBM with PD is considered a “complex type” classification of PBM. The embryological mechanism of PBM is unclear; however, there are strong arguments for an abnormal embryology of the ventral pancreas until embryonic week four [2, 3]. In contrast, it is conceivable that the embryological mechanism of PD occurs by an abnormal fusion of the ventral and dorsal pancreatic ducts because the ventral pancreas fuses with the dorsal pancreas at embryonic weeks 6–7 [4]. That is, PBM and PD are congenital anomalies that develop in the embryo at an early stage, and they may be the result of bile and pancreatic duct misarrangement. However, the genesis of the “complex type” classification of PBM is unclear, and the anatomy is also varied according to each case. In addition, few patients have been reported with PBM and PD [5]. Therefore, it is occasionally difficult for physicians and surgeons to understand the anatomy and pathophysiology of patients with PBM and PD. We herein encountered a patient with PBM and incomplete PD, and we considered that PBM and incomplete PD occurred in this case due to abnormal embryology of the ventral pancreas. If the embryological etiology of PBM and PD is an abnormal embryology of the ventral pancreas, the genesis and anatomy of the “complex type” classification of PBM is easy to understand. This case supports the idea that the embryology of PBM and PD is based on abnormal embryology of the ventral pancreas.

Although the recommended treatment for a biliary dilatation with the “complex type” classification of PBM is an extrahepatic bile duct resection and hepaticojejunostomy (biliary diversion procedure), [3] selecting the transection lines of the CBD is occasionally difficult. It is important to leave as little as possible of the bile duct unresected, and in this case, the bile duct on the pancreatic side was transected at the bifurcation of the common channel and ventral pancreatic duct so as not to leave the bile duct because drainage from the ventral pancreatic duct to the dorsal pancreatic duct can be identified by ERCP. The patient is doing well without having an acute pancreatitis due to insufficient drainage of the ventral pancreatic duct. Therefore, it is important for patients with the “complex type” classification of PBM to clear the dynamics of the ventral pancreatic juice by preoperative ERCP, and it is possible to undergo a complete resection of the bile duct on the pancreatic side.