A Case Report of Pancreatic Neuroendocrine Tumor Resected with the Preoperative Diagnosis of Gastrointestinal Stromal Tumor of the Jejunum

: A 61-year-old man was examined for cervical pain and CT showed a 9 cm tumor to the third part of the duodenum and proximal jejunum. CT /MRI showed that the tumor was separated from the pancreas body. We scheduled a laparoscopic partial resection of the intestine with a suspected diagnosis of GIST of the intestine. The tumor was adhered to both the proximal jejunum and uncinate process of the pancreas. Therefore, we converted to an open surgery and resected part of the pancreas, duodenum, and proximal jejunum including the tumor. Histopathological examination showed the tumor capsule included the tissue of the pancreas and that the border between the intestine and the tumor was clear, suggesting that the origin of the tumor was the pancreas. We diagnosed the patient as having a grade 2 pancreatic neuroendocrine tumor based on the tumor growth pattern and immunohistochemistry findings. We examined the preoperative CT images retrospectively and found that the tumor had adhered to the uncinate process of the pancreas, which extends over the left side of the superior mesenteric artery. When GIST close to the proximal jejunum is suspected, the possibility of pancreatic neuroendocrine tumor should be considered.