Pancreatic neuroendocrine tumor with abundant mitochondria.

A 40-year-old woman presented with dull, boring periumbilical region pain radiating to the back and vomiting for 1 year. Magnetic resonance cholangiopancreatography detected a polypoid growth in the ampullary region. The patient underwent Whipple's procedure. The specimen revealed a 4.9 × 4.5 × 3.7 cm tumor arising from the pancreas, abutting the posterior pancreatic surface and infiltrating the terminal common bile duct and the ampulla. Microscopic examination showed a pancreatic tumor composed of neuroendocrine cells. In addition, many large foci showing solid sheets of oncocytic cells with abundant granular eosinophilic cytoplasm were observed. Immunohistochemistry studies revealed positivity for synaptophysin, chromogranin, and Ki67 index above 70%. A diagnosis of oncocytic neuroendocrine tumor of Grade 3 was made. In electron microscopy, oncocytic cells showed abundant mitochondria dispersed throughout the cytoplasm. Oncocytic pancreatic neuroendocrine neoplasms are uncommon and can be diagnosed only on histopathological examination. These tumors tend to show a malignant behavior.