[A case of malignant oncocytoma of the parotid gland]

A case of malignant oncocytoma of the left parotid gland occurring in a 57-year-old man presenting with a painless lump is reported. The tumor was round, firm, mobile, well defined, and located in the left preauricular area. There was no evidence of facial weakness. At operation the left parotid gland was exposed to reveal a tumor arising from the superficial lobe, but involving the facial nerve. Superficial lobectomy was performed followed by reanastomosis using the great auricular nerve for the sacrificed facial nerve. Subsequently, the tumor recurred 13-months after the primary excision. The patient underwent radical neck dissection and was given supplementary radiation therapy. Because DNA-FCM of the tumor showed diploid-type with a large G2/M peak, we regarded radiation therapy as being potentially effective. Follow-up examinations performed two years later revealed no evidence of regional or distant metastases. The histologic examination of the original and the recurrent lesion showed large atypical cells, with abundant eosinophilic granular cytoplasm, which were often pleomorphic and highly-mitotic. Under ultrastructural examination, the cytoplasm contained numerous mitochondria of various shapes and sizes. These pathological findings were consisted with malignant oncocytoma.