Histopathology of the Minor Duodenal PapillaSuda K.
Departments of Pathology, Tokyo-Nishi Tokushukai Hospital and Juntendo University, School of Medicine, Tokyo, Japan
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.
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The minor duodenal papilla, which is the orifice/duodenal termination of the accessory, or dorsal, pancreatic duct/Santorini duct, mostly accompanied by pancreatic tissue, is situated in the second portion of the duodenum, typically about 2 cm ventroproximal to the major duodenal papilla.
In the following, the histopathology of the minor duodenal papilla is described.
Duodenal Termination of the Accessory Pancreatic Duct
The terminal portion of the accessory pancreatic duct (APD) is the main component of the minor papilla and is nearly always present, but often regresses during development. The patency of the terminal APD is recognized in about half or more of cases [1,2,3] and is related to the degree of fibrosis . The APD contains papillary fronds that are lined by simple columnar epithelium with some goblet cells  and encircled by a smooth muscle layer with surrounding growth (fig. 1). These muscle tissues have been the subject of controversy for more than a century regarding whether or not they form a sphincter muscle .
|Fig. 1. Minor duodenal papilla. The terminal portion of the APD is the main component of the minor papilla, accompanied by pancreatic tissue (arrows). MP = Muscularis propria. HE, ×10 (reproduced with permission from ).|
One of the important roles of the APD is the additional drainage/outflow of pancreatic juice. In cases of pancreaticobiliary maljunction, in which the junction of the pancreatic and bile ducts is located outside the duodenal wall, pancreatic juice may flow freely into the extrahepatic bile duct and also the gallbladder, resulting in a higher risk of biliary tract carcinoma . According to Kamisawa et al. , in these cases of high-level outflow of pancreatic juice into the duodenum through the APD, decreased pancreatic juice reflux into the bile duct may decrease the incidence of biliary tract carcinoma.
Pancreatic tissue was found in about 80% of cases in the minor papilla . Among these cases, the pancreatic tissue was continuous, without a gap, in the proper/original pancreas in about 20% of cases, and was also located within the muscularis propria of the duodenum, just adjacent to the proper/original site, in the other 20% of cases. Hence, the pancreatic tissue was continuous and/or closely related to the proper pancreas in about 40% of cases. The islets of Langerhans in the pancreatic tissue exhibited a round or oval shape with a few pancreatic polypeptide (PP) cells , similar to those of the dorsal pancreas [9,10]. Acinar cells showed positive immunoreactivity for anti-amylase, revealing functioning as in the exocrine pancreas . Although the pancreatic tissue in the minor papilla was considered ectopic , based on the continuous tissue expansion to the proper site, and exhibited the same exocrine and endocrine morphologies/functions, it might be a portion of the dorsal pancreas.
Endocrine Cell Micronests
Endocrine cell micronests are frequently found in the minor papilla, especially in the ductal wall/surrounding area of the terminal APD (fig. 2). Their frequency was 52.2% in autopsy cases, being more frequent than those of the major papilla . Endocrine cell micronests predominantly consist of somatostatin- and PP-containing cells, and most of the cells staining for somatostatin also contained PP [8,11]. In our previous study, PP cells were selectively found in the ventral pancreas and were stained positive for anti-serotonin, but not for anti-somatostatin . Hence, endocrine cell micronests are a characteristic finding in the minor papilla.
|Fig. 2. Endocrine cell micronests (arrows) are present in the ductal wall/surrounding area of the terminal APD. Immunostaining for chromogranin A, ×200 (reproduced with permission from ).|
The significance of PP cells in the minor papilla remains unknown, but might be related to movement of the APD, because the common bile duct ran into the ventral pancreas, which is abundant in PP cells.
Pancreas divisum is a congenital anomaly in which the dorsal and ventral pancreatic ducts do not unite or communicate, and separately drain into the two duodenal papillae. Under this condition, pancreatic juice from the dominant dorsal moiety flows out only through the minor papilla, in which the outlet is notably small in most cases . Subsequently, inadequate pancreatic juice drainage from the minor papilla may occur, called dorsal pancreatitis, a kind of chronic obstructive pancreatitis, which shows inter- and intralobular fibrosis with atrophy or disappearance of the acinar cells/lobuli.
Tumor of Minor Duodenal Papilla
In the minor duodenal papilla, all ductal tumors may occur, such as intraductal papillary mucinous neoplasms and invasive ductal carcinomas, but carcinoid tumors are less frequent in the minor than in the major papilla .
Koichi Suda, MD
Department of Pathology, Tokyo-Nishi Tokushukai Hospital
3-1-1 Matsubara-cho, Akishima-shi
Tokyo 196-0003 (Japan)
Tel. +81 42 500 4433, Fax +81 42 500 6632, E-Mail email@example.com
Published online: June 10, 2010
Number of Print Pages : 3
Number of Figures : 2, Number of Tables : 0, Number of References : 12
Vol. 27, No. 2, Year 2010 (Cover Date: June 2010)
Journal Editor: Büchler M.W. (Heidelberg), Neoptolemos J.P. (Liverpool)
ISSN: 0253-4886 (Print), eISSN: 1421-9883 (Online)
For additional information: http://www.karger.com/DSU