[Diffuse hyperplastic oncocytosis of the parotid gland]

Oncocytes are epithelial cells characterized by an granular, eosinophilic cytoplasma, and a centrally situated, pycnotic nucleus. These cells were first observed by Hamperl 1931 in the salivary glands. Ultrastructural studies have shown that the cytoplasma of these cells is filled with numerous large and bizarre mitochondria. The exact biological significance of oncocytes is unknown - Becker, Donath and Seifert suggest an intracellular metabolic disturbance associated with mitochondriopathy, caused by an age dependent metabolic defect. Oncocytes are not specific for the salivary glands; they are also found in the thyroid gland, parathyroid gland, liver, pancreas, esophagus and the kidney. Solitary oncocytes appear most often as incidental findings in aging salivary tissue, they are present in persons older than 70 years up to 80 %. The diffuse hyperplastic oncocytosis of the parotid gland represents an extremely rare, non-tumorous alteration of the parotid gland. Caused by an extensive metaplasia of acinic and ductal cells nearly the entire gland consists of oncocytes. Clinically it is characterized by swelling of the parotid gland. Oncocytic adenomatous hyperplasia is a different disease. It represents a multifocal oncocytic proliferation of the duct system. In contrast to diffuse oncocytosis remnants of the original salivary tissue with acini and fatty tissue are usually present between the oncocytic nodules. Typical oncocytomas may possibly develop from such oncocytic proliferation by a tendency to confluent growth.

Cases of diffuse hyperplastic oncocytosis of the parotid gland were identified by literature review.

Worldwide diffuse hyperplastic oncocytosis of the parotid gland has been observed in 8 cases (Fig. ) as of today.

We report and discuss the case of a 78-year-old male, who was refered to our hospital because of a painless mass of the left parotid gland. MRI showed a tumorous lesion with a diameter of about 5 cm. Lateral parotidectomy was performed. Histology revealed an extremely rare case of diffuse hyperplastic oncocytosis. There has been no recurrence of tumor after 2 years.

Diffuse hyperplastic oncocytosis of the parotid gland is an extremely rare benign disorder, complete excision of the tumor-like lesion is curative. In literature there has been no report of recurrence, malignant transformation or metastasizing illness.