Multifocal nodular oncocytic hyperplasia of bilateral parotid glands: A case report with a histological variant of clear cells.

A case of multifocal nodular oncocytic hyperplasia (MNOH) of the bilateral parotid gland is presented. An 80-year-old woman was admitted to hospital because of painless swellings in bilateral parotid regions. Histologically, the nodular lesion had incomplete capsules and engulfed the surrounding parotid gland at the periphery. The lesions were mostly composed of clear cells, while the peripheries of the lesions had typical oncocytic cells with abundant fine granules. The histological existence of the clear cell component in the lesions led to misdiagnoses of other clear cell neoplasms. However, this case had multiple nodules in bilateral glands. No evidence of malignant histological findings was found. Moreover, the clear cells, as well as the oncocytic cells, were demonstrated to have mitochondria and glycogen in their cytoplasm using special staining. Based on these findings, the diagnosis of this case was MNOH in the parotid gland. We also discuss the differential diagnosis for clear cell lesions.