A Case of Oncocytomatous Carcinoid

A 74-year-old asymptomatic male was admitted because of abnormal chest X-ray findings. Chest films showed a tumor shadow in the left lower lung field. The tumor which obstructed the basal bronchus, was recognized by bronchofiberscopy. Left lower lobectomy was carried out. The tumor, 8×3×2.5 cm, extended from B9+10 into the lumen of basal bronchus, which was occluded. Invasion to lung parenchyma was not recognized. Microscopical examination of tumor cells showed abundant granular, eosinophilic cytoplasm, and round nucleis. In the cytoplasm of some tumor cells grimelius stain revealed many argyrophilic granules, but their contents were not defined by immunochemical methods. Electron microscopy showed mitochondrial hyperplasia and a few small dense core granules. Judging from these characteristic histological findings, this tumor was diagnosed as a rare case of oncocytomatous carcinoid.