[A Case of Invasive Intraductal Papillary Mucinous Carcinoma of the Pancreas with Portal Annular Pancreas].

A 70-year-old male patient presented with epigastric pain. Subsequent evaluation revealed a cystic lesion in the head of the pancreas. After 1 year, the cyst had enlarged and a nodular shadow appeared within it, prompting a referral to our hospital. CT imaging revealed a 65 mm cystic lesion extending from the head to the uncinate process of the pancreas, located posterior to the portal vein. Additionally, an indistinct nodule was apparent inside the cyst. Based on a diagnosis of invasive intraductal papillary mucinous carcinoma, pancreaticoduodenectomy was performed. Intraoperative findings revealed that the uncinate process of the pancreas, which was continuous with the tumor, was fused with the dorsal pancreas. The dorsal pancreas, including the main pancreatic duct, was dissected first. Then, the uncinate process was resected from the dorsal pancreas at the fusion site using a linear stapler. Postoperatively, the patient developed a Grade B pancreatic fistula, which was successfully managed with conservative treatment. It has been reported that the portal annular pancreas poses a higher risk of postoperative pancreatic fistula following pancreaticoduodenectomy. This case highlights the challenges in the preoperative diagnosis of portal annular pancreas when a tumor is located in the uncinate process of the pancreas.