Ampulla of Vater

Primary Site. The ampulla is a small dilated duct less than 1.5 cm long, formed in most individuals by the union of the terminal segments of the pancreatic and common bile ducts (Figure 23.1). In 42% of individuals, however, the ampulla is the termination of the common duct only, the pancreatic duct having its own entrance into the duodenum adjacent to the ampulla. In these individuals, the ampulla may be difficult to locate or even nonexistent. The ampulla opens into the duodenum, usually on the posterior-medial wall, through a small mucosal elevation, the duodenal papilla, which is also called the papilla of Vater. Although carcinomas can arise either in the ampulla or on the papilla, they most commonly arise near the junction of the mucosa of the ampulla with that of the papilla. It may not be possible to determine the exact site of origin for large tumors. Nearly all cancers that arise in this area are well-differentiated adenocarcinomas.