Incidentally detected pancreatic neuroendocrine microadenoma with lymph node metastasis

Pancreatic neuroendocrine microadenomas (NEMAs) are non-functioning neuroendocrine tumors < 0.5 cm with a low proliferation rate and are considered benign. We report on a pancreatic NEMA with lymph node metastasis. A male in his 70s had pylorus-preserving pancreaticoduodenectomy for a distal bile duct carcinoma, which was a 2.1 cm well-differentiated-infiltrating adenocarcinoma with invasion limited to the bile duct wall. An incidental separate 0.4 cm well-differentiated NEMA was found in the pancreatic head with metastatic well-differentiated neuroendocrine tumor in one peripancreatic lymph node. Both neuroendocrine tumors in the pancreatic head and in the lymph node were composed of nests of uniform neoplastic cells with a fine chromatin pattern. The Ki-67 labeling index of NEMA was 0.85%. The neoplastic neuroendocrine cells in both the pancreas and node were diffusely positive for synaptophysin, chromogranin, and insulin. Therefore, this unusual case provides an exception to the current classification system which regards NEMAs as benign lesions.