Oncocytic carcinoma of the parotid gland: A rare malignancy with diagnostic and therapeutic challenges

Abstract

Oncocytic carcinoma of the parotid gland is an exceptionally rare malignancy, accounting for approximately 0.18% of all salivary gland cancers. Its diagnosis is often delayed due to overlapping clinical and radiologic features with benign oncocytic tumors such as oncocytoma and Warthin tumor. We report the case of a 64-year-old man who presented with a progressively enlarging right parotid mass over 4 months, accompanied by new-onset facial nerve palsy and trismus. MRI revealed a multilobulated, ill-defined, heterogeneously enhancing mass in the superficial lobe of the right parotid gland, without overt signs of perineural spread. Despite the absence of clear radiological evidence of nerve invasion, intraoperative findings confirmed extensive tumor infiltration of the facial nerve, requiring its complete sacrifice. Histopathological examination, complemented by immunohistochemical analyses demonstrating strong CK7 and PAX8 expression, was essential in confirming the diagnosis of oncocytic carcinoma and distinguishing it from benign oncocytic lesions. This case highlights the limitations of conventional imaging in detecting perineural invasion and underscores the importance of integrating clinical, surgical, and detailed histopathologic evaluation, including immunohistochemistry, in managing atypical parotid tumors.