Pulmonary oncocytoma

The fine structure of a pulmonary oncocytoma was compared with that of a typical bronchial carcinoid, in an effort to determine the histogenesis of this rare neoplasm. The oncocytoma cells contained large argyrophilic secretion vesicles with dense core aggregation typical of endocrine tissue. Smaller secretion granules were present in both the carcinoid and oncocytoma. Large dense core vesicles were not found in the carcinoid, but other ultrastructural characteristics of the neoplasms were similar. Available evidence suggests that the oncocytoma is a morphologic variant of the bronchial carcinoid and is not of exocrine gland origin. The oncocytic appearance of the pulmonary tumor via light microscopy was related to the large secretion vesicles within the cells rather than to mitochondria. In “oncocy-tomas” of other organs, the eosinophilic granular cytoplasm reflects cytoplasmic packing by large mitochondria. Pulmonary oncocytoma is best differentiated from metastatic or primary carcinoma by the absence of mitoses.