An Intraductal Papillary Mucinous Neoplasm-Like Lesion Manifesting as a Duodenal Polyp: A Rare Case Report.

Intraductal papillary mucinous neoplasms (IPMNs) typically originate within the pancreatic ductal system. However, the occurrence of an IPMN-like mucinous neoplasm outside the pancreas, presenting as an isolated duodenal polyp, is extremely rare. An asymptomatic 64-year-old woman underwent routine screening endoscopy, which revealed a 25-mm Yamada type IV pedunculated polypoid lesion in the second portion of the duodenum. En bloc endoscopic mucosal resection was performed without procedural complications, although histological evaluation revealed focal involvement of the deep resection margin. Histopathological examination demonstrated a mucinous neoplasm confined within the duodenal submucosa with papillary architecture and low-grade dysplasia, which was designated as a duodenal IPMN-like lesion. Post-procedural CT showed no concurrent pancreatic involvement, and endoscopy at 6 months demonstrated a stable post-resection scar without local recurrence. Extended follow-up with dedicated pancreatic imaging is ongoing. This case report describes a particularly uncommon duodenal IPMN-like lesion presenting as a polyp. This case highlights the importance of careful histological evaluation and the inclusion of pancreaticobiliary-type neoplasms in the differential diagnosis of atypical periampullary lesions, along with long-term surveillance.