Challenges in the Cytodiagnosis of Intraparotid Schwannoma

Clear cell tumors of parotid gland encompass a wide spectrum of neoplasms, including benign and malignant epithelial neoplasms. Additionally, tumors from adjacent structures such as paraganglioma, and metastatic neoplasms may also show clear cells. Overlapping cytological features may cause difficulty in diagnosis. This 50-year-old female presented with inability to close the right eye for 4 years, and with an infra-auricular swelling. Fine-needle aspiration cytology (FNAC) done outside was submitted for review with a diagnosis of neuroendocrine tumor. Smears showed clusters of tumor cells with abundant vacuolated cytoplasm and uniform round to ovoid nuclei. Features were those of salivary gland neoplasm of uncertain malignant potential, that is Milan category IVB: cellular neoplasm with clear cell features, with differential diagnoses of myoepithelial cell neoplasms, acinic cell carcinoma and paraganglioma. FNAC repeated for better characterization showed similar polygonal cells, accompanied by few spindle-shaped cells with ovoid nuclei, suggestive of paraganglioma. However, DOTANOC uptake was absent. Patient underwent radical parotidectomy; intraoperative frozen section showed a spindle cell tumor. Final histopathology revealed an intraparotid facial nerve schwannoma. The tumor was multi-nodular, with some nodules being composed almost entirely of polygonal cells with clear cytoplasm, that is, Antoni B areas, and others showing typical Antoni A areas admixed with Antoni B areas. Parotid FNAC has high accuracy for diagnosis of epithelial lesions; however, mesenchymal tumors often pose a diagnostic difficulty. Intraparotid schwannoma is not uncommon and may be diagnosed easily on FNAC when morphology is classical. However, intra-tumoral heterogeneity and less common histological subtypes may present a pitfall in cytodiagnosis.