Non-invasive Intraductal Oncocytic Papillary Neoplasm Forming a Protruding Lesion Toward the Duodenum from the Accessory Papilla: a Case Report.

BACKGROUND:Intraductal oncocytic papillary neoplasm (IOPN), previously classified as a subtype of intraductal papillary mucinous neoplasm (IPMN), has been described as an independent disease by the WHO since 2019. IOPN is a rare tumor, with few reported cases. Herein, we report a case of resected non-invasive IOPN that formed a lesion protruding toward the duodenum from the accessory papilla.CASE PRESENTATION:An 80-year-old woman was referred to our hospital because of a giant mass in the pancreatic head detected on abdominal contrast-enhanced computed tomography (CT) performed for a close examination of a mass in the right breast. CT revealed a 90-mm-sized tumor with a mixture of solid and cystic components, with contrast enhancement in the pancreatic head, and a dilated main pancreatic duct. Esophagogastroduodenoscopy revealed a semi-circumferential papillary tumor protruding toward the duodenal lumen, which did not protrude from the papilla of Vater. Transpapillary biopsy led to a preoperative diagnosis of IPMN with an associated invasive carcinoma. As there were no distant metastasis, open subtotal stomach-preserving pancreaticoduodenectomy was performed. Analysis of the surgical specimen and histopathological examination revealed that the tumor was an IOPN that protruded toward the duodenal mucosa from the accessory papilla while replacing the duodenal mucosa with no obvious stromal invasion.CONCLUSION:IOPN is a rare and poorly recognized tumor with few reported cases. There have been no reports describing IOPN forming a protruding lesion toward the duodenum from the accessory papilla. Therefore, further accumulation of cases such as this one is important to advance the study of IOPN.