Pleomorphic adenoma: Cytologic variations and potential diagnostic pitfalls

The diverse morphological features encountered in pleomorphic adenoma (PA) may cause diagnostic errors in fine needle aspiration cytology (FNAC). The present study was performed to evaluate the variations in the cytological features of pleomorphic adenoma and to assess the efficacy of FNAC in its diagnosis. Fifty cases diagnosed as PA on FNAC were retrieved from the records of the Pathology Department. Cytologic smears and sections were reviewed and the cytologic diagnoses were compared with the definitive histologic diagnoses. In cases correctly diagnosed on aspiration, morphological variables like patterns of the epithelial component, type and extent of the mesenchymal matrix, metaplastic cells, hyaline globules, cystic change, giant cells, crystalline deposits, nuclear inclusions/grooves, and nuclear atypia were evaluated. The extreme diversity in morphologic features seen in histologic sections was reflected in the smears of PA. Metaplastic changes were observed more frequently in sections, while nuclear changes like inclusions/grooves were more commonly seen in smears. Other morphological features like cylindromatous pattern, giant cells and crystalline deposits were observed with equal frequency in smears and sections. Cytohistologic agreement was present in 45 of the 50 cases (90%). In 5 cases diagnosed as pleomorphic adenoma on FNAC, the histology revealed 1 case each of schwannoma, perineurioma, ectomesenchymal chondromyxoid tumor of tongue, adenoid cystic carcinoma and mucoepidermoid carcinoma. FNAC is a fairly accurate pre-operative procedure for the diagnosis of PA. The cytopathologist needs to be aware of the cytologic variations in pleomorphic adenoma so as to avoid diagnostic errors.