Mucinous carcinoma of Vater's ampulla with a unique extension along the main pancreatic duct.

We report a case of mucinous carcinoma of Vater's ampulla with a unique extension along only the main pancreatic duct (MPD) and microinvasion to the pancreas. A 52-year-old man was referred to our hospital for the evaluation and treatment of acute pancreatitis. Abdominal computed tomography (CT) demonstrated swelling in the head of the pancreas with a mass in the duodenum. Hypotonic duodenography and endoscopic examination revealed a well-defined mass, measuring about 25 mm in size, in Vater's ampulla. A biopsy specimen of the tumor showed moderately differentiated adenocarcinoma. A pylorus-preserving pancreaticoduodenectomy with a regional lymphadenectomy was performed, under a preoperative diagnosis of adenocarcinoma of Vater's ampulla with direct invasion into the head of the pancreas. The resected specimen of the duodenum confirmed the presence of the mass, which measured 22 x 15 mm in size, in Vater's ampulla. Microscopically, the tumor consisted of two components: moderately differentiated adenocarcinoma in the peripheral region of the tumor Vater's papilla and mucinous carcinoma in the central region of the tumor. The mucinous carcinoma component uniquely extended along only the MPD with microinvasion to the pancreas. Immunohistochemically, both the moderately differentiated adenocarcinoma and the mucinous carcinoma were positive for cytokeratin 20 (CK20) and negative for cytokeratin 7 (CK7) which is the pattern of intestinal-type carcinoma of Vater's ampulla. We concluded that the original site of this tumor may have been the duodenal epithelium of Vater's ampulla originally moderately differentiated adenocarcinoma-which subsequently changed to mucinous carcinoma that extended along only the MPD with microinvasion to the pancreas.