A Case of Difficult Diagnosis between Intraductal Tubulopapillary Neoplasm and Intraductal Papillary Mucinous Neoplasm

Abstract

We report a case of an intraductal tumor presenting as a nodule in the accessory pancreatic duct, which was difficult to distinguish postoperatively from intraductal tubulopapillary neoplasm (ITPN) and intraductal papillary mucinous neoplasm (IPMN). A 56-year-old man was referred to our hospital following the detection of a dilated pancreatic duct on abdominal ultrasonography during a physical examination. Further evaluation revealed a nodular tumor in the accessory pancreatic duct and erosion with a dent in the duodenal mucosa. The preoperative diagnoses included pancreatic divisum, ITPN in the accessory pancreatic duct, and duodenal invasion. A subtotal stomach-preserving pancreaticoduodenectomy was performed. In the specimen, a 15 × 9 mm tumor was found in the accessory pancreatic duct, and the atypical epithelium without mucin grew papillary and tubular structures. The tumor partly invaded the duodenal muscle layer. Immunohistochemical staining was negative for MUC1 and MUC6 but positive for MUC2 and MUC5AC. Although ITPN was initially suspected based on clinical features, immunohistochemical findings were more consistent with IPMN, making the final pathological diagnosis challenging.