Cytomorphological spectrum of pleomorphic adenoma with emphasis on differential diagnosis and diagnostic pitfalls

Introduction: Pleomorphic adenoma exhibit wide morphological spectrum varying from predominantly epithelial types to predominantly stromal types which often pose diagnostic challenge to cytopathologists. Aim: The aim of the present study was to evaluate varied cytomorphological features of pleomorphic adenoma with an emphasis on differential diagnosis and to highlight diagnostic pitfalls. Materials and Method: This was a retrospective study from January 2011 to December 2015 in our Department of Pathology. During this period 220 patients with salivary gland space occupying lesions underwent FNAC, out of which 190 aspirates were satisfactory for evaluation, 75 aspirates were reported as pleomorphic adenoma and these 75 cases were reviewed by two cytopathologists independently for cytomorphological findings, diagnosis and differential diagnosis where needed. Results: On revised cytology 67 cases out of the 75 cases reported initially as pleomorphic adenoma were concordant with the earlier diagnosis. The remaining 8 cases on revised reporting were diagnosed as adenoid cystic carcinoma in 5 cases, mucoepidermoid carcinoma in 2 cases and basal cell adenoma in one case. The cytological smears of 67 cases of pleomorphic adenoma were categorized on basis of cellularity as mild (4.477%), moderate (44.776%) and marked (50.746%) as well as for ratio of epithelial to mesenchymal component. Varied morphological variations like squamous metaplasia (17.9%), mucinous metaplasia (2.9%), oncocytic change (5.9%), hyaline globule (2.9%), giant cells(4.47%), cystic degeneration (22.38%) and plasmacytoid cell differentiation (32.83%) were observed in cytological smears of pleomorphic adenoma. Conclusion: We conclude that adequate and representative sample is essential for proper cytological examination, further Romanowasky stain is mandatory for FNA of salivary gland lesions. Cytopathologists should be aware of varied cytomorphological characteristic of pleomorphic adenoma in order to minimize the possibility of diagnostic errors.