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Difficulty in the intraoperative identification of a small non-functional pancreatic neuroendocrine tumor detected by FDG-PET: A case report

A 74 ― year ― old man was referred for removal of a 10 mm mass in the uncinate process of the pancreas, identified by increased fludeoxyglucose (FDG) uptake (SUVmax 4.32) on a FDG ― positron emission tomography ― computed tomography (PET/CT) scan, performed during preoperative workup for thyroid carcinoma. A contrast ― enhanced CT scan showed a 7 mm early ― enhancing mass at the same site. This was diagnosed as a pancreatic neuroendocrine tumor (PNET). A partial pancreatectomy was performed as an excisional biopsy with intraoperative ultrasonography. No tumor was found in the resected specimen, but was seen on CT during follow ― up. Four months after the first resection, we performed a repeat partial pancreatectomy. Three resections were performed, but the tumor was not found in the resected specimens by frozen section examination. Therefore, we finally performed a subtotal stomach ― preserv-ing pancreaticoduodenectomy. On pathological examination, we finally located a 7 mm tumor in the specimen following detailed analysis. This tumor was immunohistochemically positive for synapto-physin, chromogranin A, and CD56. The Ki ― 67 index was less than 1.5%. The mass was diagnosed as a PNET (WHO classification Grade 1). We report our experience with difficulty in intraoperative identification of a small PNET.