Fine Needle Aspiration Cytology of Cutaneous Adnexal Tumours-Navigating a Field Full of Landmines!

BACKGROUND: Cutaneous adnexal tumours are uncommon and are rarely diagnosed clinically. Occasionally, these cases are encountered during fine-needle aspiration cytology (FNAC) performed as part of the routine evaluation of skin or subcutaneous tissue lesions. MATERIALS AND METHODS: This retrospective study evaluated FNAC of skin adnexal tumours over a period of 10 years. Smears stained with Papanicolaou and Giemsa stains were reviewed. Cytology diagnosis was correlated with histopathological diagnosis, wherever possible. RESULTS: A total of 34 cases of skin adnexal tumours were evaluated in the study. None of the cases had been diagnosed clinically. Most patients were in the 2nd-4th decades of life, with a male predominance. The head and neck region was the commonest site of involvement. Of the 34 cases, 32 (94.1%) were diagnosed as benign and 2 (5.9%) as malignant. Tumour subtyping on FNAC was possible in only 11 cases, comprising seven cases of pilomatrixoma and four cases of eccrine spiradenoma. Histopathological correlation was available in 13 cases, of which 10 showed concordance with the cytological diagnosis. The three discordant cases were pilomatrixoma and trichoblastoma, which had been misdiagnosed as malignant adnexal tumour on FNAC and a squamous carcinoma that was mistaken for a pilomatrixoma on FNAC. CONCLUSIONS: FNAC can play a valuable role in the preoperative diagnosis of cutaneous adnexal tumours. However, the cytological diagnosis of these tumours remains challenging. Correlation with clinical features, familiarity with the varied cytomorphological features and awareness of potential diagnostic pitfalls can minimise diagnostic errors.