Navigating the Differential Diagnosis for Oncocytic Salivary Gland Lesions (Cytology and Histology)

Abstract Oncocytic lesions of the parotid gland include nonneoplastic entities and benign and malignant neoplasms. The most common benign neoplasm is Warthin tumor, which can be correctly diagnosed using fine-needle aspiration (FNA) or core biopsy in most cases. However, accurate FNA and/or biopsy preoperative diagnosis of many entities in this category is limited by sampling and overlap in morphological features among the different entities. We report the case of a 77-year-old man who presented with a right parotid mass identified on magnetic resonance imaging and computed tomography scan that was cystic with necrosis and with possible papillary growth in the cyst. The FNA smears were scantly cellular, with a few representative groups with significant nuclear crowding and overlapping in a bloody background. The cells had oncocytic cytoplasm, an increased nuclear-to-cytoplasmic ratio, and round-to-oval nuclei with prominent nucleoli. Necrosis, mitoses, and significant nuclear pleomorphism were not identified. The findings were interpreted as consistent with an oncocytoid/oncocytic salivary gland neoplasm. The cell block was acellular, so the neoplasm could not be further characterized by ancillary studies. The patient underwent a right superficial parotidectomy. The histopathological diagnosis was oncocytic carcinoma primarily based on the identification of perineural invasion. Oncocytic carcinoma is a rare, high-grade malignancy of salivary glands. This case will be used to discuss the differential diagnosis of oncocytoid/oncocytic salivary gland lesions on both cytopathology and histopathology and provide a pragmatic approach to the diagnostic evaluation. Indications for available ancillary testing will also be reviewed.