Extensive squamous metaplasia with cystic change in pleomorphic adenoma: A potential diagnostic pitfall in fine needle aspiration cytology

Pleomorphic adenoma (PA) is the most common salivary gland tumor, frequently affects the parotid gland. Histological diversities are common as PA may show mucous, sebaceous, oncocytic cells, and squamous metaplastic cells. Squamous metaplasia rarely results in formation of extensive keratin-filled cyst lined by squamous epithelium. This can be mistaken for malignancy, like squamous cell carcinoma and mucoepidermoid carcinoma on cytological interpretation, due to limited and selective sampling. Here, we report a case of slowly enlarging parotid mass in a 70-year-old male. Cytological smears revealed moderately atypical squamous cells, clumps of keratin material, necrosis, inflammatory cells and macrophages along with bland epithelial and myoepithelial cell in fibromyxoid stroma. Cytological diagnosis of squamous cell carcinoma ex-pleomorphic adenoma was suspected. Subsequent resection showed pleomorphic adenoma, with extensive squamous metaplasia and cystic change on histology. There was no evidence of squamous cell carcinoma. The cytopathology findings are probably related to ischemic infarction, which mimic malignancy. This case emphasizes the need for a cautious and systematic approach in the cytological interpretation of cystic pleomorphic adenoma with metaplastic epithelial changes. We discuss the pitfall in the cytological diagnosis including differential diagnosis of this uncommon presentation.