Fine needle aspiration cytomorphology of parotid gland oncocytoma: a case series

Salivary gland oncocytoma is a benign tumor consisting of oncocytes, which are epithelial cells characterized by abundant eosinophilic cytoplasm due to mitochondria accumulation. Fine needle aspiration (FNA) is commonly employed as a primary diagnostic tool in evaluation of salivary gland lesions. Per the 2nd edition of the Milan System for Reporting Salivary Gland Cytopathology, oncocytoma can be classified as benign when supported by clinicoradiographic findings and ancillary studies. However, in practice, oncocytoma is typically indeterminately classified on FNA. We assessed clinical and cytologic features of ten oncocytoma cases to identify key morphologic features that could enhance diagnostic interpretation.

In this retrospective study, we reviewed FNA findings in cases of resection-confirmed oncocytoma. Cytologic diagnoses and clinicoradiographic findings were analyzed. All slides were reviewed for morphologic features, including architectural, cytoplasmic, and nuclear features.

Ten cases were identified, all from the parotid gland. None were specifically diagnosed as oncocytoma on FNA. All patients were nonsmokers and no invasion was identified on imaging. All cases displayed benign oncocytes with granular eosinophilic cytoplasm in acinar/organoid arrangements within cohesive tissue fragments, which architecturally resembled normal salivary gland acini. Absent were features of malignancy, such as atypia, mitoses, necrosis, cytoplasmic vacuolization, or loss of cohesion.

Tightly-cohesive tissue fragment arrangements of bland oncocytes are characteristic of parotid gland oncocytoma on FNA, and benign classification may be favored in the correct clinicoradiographic context. Additional studies are necessary to determine if oncocytoma can be reliably distinguished from "oncocytoid" salivary carcinomas by cytomorphology.