What is pancreas divisum?

A congenital anomaly of failure of fusion of the dorsal and ventral pancreatic buds, resulting in two ducts. The main pancreatic duct drains through the minor papilla and is seen to cross the common bile duct (rather than join it) on MRCP or ERCP. The lesser duct (the duct of Santorini), rather than the major duct (the duct of Wirsung), drains most of the pancreas. The minor papilla may be too small to allow adequate drainage, leading to pancreatitis.