Oncocytoma (mitochondrioma) of the parotid gland. An electron microscopical study.

Electron microscopical study of an oncocytoma of the parotid gland disclosed the presence of two cell types, typical oncocytes and condensed oncocytes. The typical oncocyte contains abundant mitochondria that were tightly packed almost completely filling the entire cytoplasm. Only small areas were left for the remaining cytoplasmic organelles. The nuclei in these typical onocytes appeared oval or spheroid. Condensed oncocytes were scattered singly or in nests in tumorous tissue. These cells were also replete with mitochondria, but differed, however, in that many mitochondria showed evidence of degeneration and fusion. Nuclei of these cells were irregular, dense, and contained inclusions and glycogen granules. The relationship of nuclear envelopes to mitochondria and other cellular components has been described previously, but to our knowledge, this represents an original finding in the case of an oncocytoma.