Ultrastructure of bronchial oncocytoma

A bronchial neoplasm consisted of cells with abundant, finely granular, eosinophilic cytoplasm. Ultrastructurally, this granularity was due to mitochondrial hyperplasia thus fulfilling the criterion of a true oncocyte. Although the terms “pulmonary oncocytoma” and “oncocytic carcinoid” have been used in the past, this is apparently the first pulmonary tumor in which mitochondrial hyperplasia has been demonstrated thereby confirming the accuracy of the term oncocytoma in this particular instance. The bronchial mucosal glands adjacent to the tumor contained numerous foci of oncocytes and are considered the most likely source of the neoplasm.