Structure and Shape of the Papilla of Vater

The papilla of Vater, also called the major papilla, which is usually situated medially at the midportion of the second part of the duodenum, is a cylindrical protuberance that houses a common channel or the terminations of the common bile duct (CBD) and main pancreatic duct (MPD) (fig. 1). In most cases, especially among Japanese, both ducts join within the duodenal wall [1] and have a short common chamber, named an ampulla or the common channel (fig. 2).

Fig. 1. Longitudinal section of the PV (3 days, F). The CBD and the MPD merge and formed a common channel. HE. Low magnification. CBD = Common bile duct; MPD = main pancreatic duct; PV = papilla of Vater. (Reproduced with permission from [7].)

Histologically, the papilla of Vater is covered by a triangular fold of the duodenal mucosa along the outer surface including the plica longitudinalis. The duodenal mucosa in the region immediately surrounding the outlet of the common channel, where CBD and MPD join, is covered by a sheath of epithelium with small villi. In contrast, the ampullary or intrapapillary mucosa is present with numerous papillary processes that are much larger than those of the duodenal villi, and form valvules at the orifice. The transition from the mucosa of the ampulla or the pancreaticobiliary duct to the duodenal mucosa is more abrupt and occurs just at the outlet of the ampulla or the outer edge of the papilla of Vater, and such areas of transition are inherently unstable [2]. Hence, the region surrounding the outlet of the common channel/pancreaticobiliary duct is simply covered by ampullary and duodenal mucosae. Therefore, the 'papillary mucosa' is morphologically and anatomically equal to the ampullary mucosa, but not to the duodenal mucosa.

Normally, the plica longitudinalis at the papilla of Vater is prominently protuberated, and reflects a transition between the termination of the CBD/ MPD and the common channel, as mentioned above (figs. 1-3). In cases with t • 1 I I I I I 1 I

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