Rapidly Progressive Neuroendocrine Carcinoma of the Ampulla of Vater Detected During Intraductal Papillary Mucinous Neoplasm Surveillance.

A 77-year-old woman undergoing surveillance for an intraductal papillary mucinous neoplasm (IPMN) was found to have new enlargement of the major papilla on esophagogastroduodenoscopy. Contrast-enhanced computed tomography and endoscopic ultrasound (EUS) revealed an ampullary mass with multiple hepatic lesions. Because no tumor exposure was evident on the duodenal mucosal surface, endoscopic ultrasound-guided fine-needle biopsy (EUS-FNB) was performed. Histopathological and immunohistochemical findings, including a high Ki-67 labeling index, confirmed the diagnosis of neuroendocrine carcinoma (NEC). The lesion had not been detected on esophagogastroduodenoscopy 12 months earlier, and magnetic resonance cholangiopancreatography obtained two months before diagnosis had not raised suspicion of ampullary malignancy. Despite biliary drainage and carboplatin-etoposide chemotherapy, the disease progressed rapidly, and the patient died four months after diagnosis. This case highlights the aggressive clinical course of ampullary NEC and the importance of careful evaluation of newly detected ampullary changes during IPMN surveillance. It also demonstrates the practical usefulness of EUS-FNB for establishing a pathological diagnosis in a non-exposed ampullary lesion.