Histopathology of the minor duodenal papilla

The minor duodenal papilla, which is the orifice of the accessory, or dorsal, pancreatic duct/Santorini duct, mostly accompanied by pancreatic tissue, is situated about 2 cm ventroproximal to the major duodenal papilla. The patency of the terminal accessory pancreatic duct (APD) is recognized in about half or more of cases, and is related to the degree of fibrosis. The APD is lined with simple columnar epithelium and encircled by a smooth muscle layer. It is still controversial whether or not these muscle tissues comprise a sphincter muscle. Pancreatic tissue was found in about 80% of cases in the minor papilla. Among these cases, pancreatic tissue was continuous and/or closely related to the proper pancreas in about 40% of cases, and might have the same exocrine and endocrine morphologies/functions, suggesting that it is a portion of the dorsal pancreas and not an ectopic one. Endocrine cell micronests are frequently found in the ductal wall/surrounding area of the terminal APD, and predominantly consist of somatostatin- and/or pancreatic-polypeptide-containing cells. In cases of pancreas divisum, inadequate pancreatic juice drainage from the minor papilla might occur, resulting in dorsal pancreatitis. In the minor papilla, all ductal tumors may occur, such as an intraductal papillary mucinous neoplasms and invasive ductal carcinoma, but carcinoid tumors are rare.