[Diffuse oncocytosis of the parotid gland. Definition and differential diagnosis]

Diffuse oncocytosis represents an extremely rare, nontumourous alteration of the parotid gland which could be observed in only 2 cases in a group of over 7000 salivary gland cases. Viewed under the light microscope, the glandular lobuli show complete oncocytic metaplasia of the acinar cells and the duct epithelia. The oncocytic cells are characterized by a swollen granular acidophilic cytoplasm. In semi-thin sections, transformed oncocytic clear basal cells are found in the vicinity of typical oncocytes. The electron microscope shows that the oncocytes contain multiple mitochondria in the cytoplasm. The mitochondria are almost always swollen, display cristolysis very often and contain osmiophilic granules. The ductular oncocytes are characterized by isolated tonofilaments, whereas the myoepithelial oncocytes are notable for peripherally arranged myofilaments. The endothelial cells of the vessels show hydropic swelling. Ultrastructural changes are observed in the terminal axons of the vegetative nervous system of the parotid gland. Diffuse oncocytosis is an intracellular metabolic disturbance associated with mitochondriopathy. Its occurrence in elderly persons is suggestive of an age-dependent metabolic defect. In differential diagnosis, diffuse oncocytosis must be differentiated from sialadenosis which is a primarily vegetative neuropathy with secretory disturbance of the acinic cells, and from oncocytic neoplasias, especially from oncocytomas and cystadenolymphomas. Oncocytic adenomatous hyperplasia is a different disease. It represents a multifocal oncocytic proliferation of the duct system. Typical oncocytomas may perhaps develop from such oncocytic proliferation by a tendency to confluent growth.