Unmasking Nodular Hidradenoma: Navigating Deceptive Cytological Patterns with Atypical Squamous Differentiation

Abstract Atypical squamous cells in hidradenoma cytology, often detached and degenerated in cystic fluid, can mimic squamous cell carcinoma (SCC). Squamous differentiation requires careful assessment to avoid overcalling malignant transformation. A 53-year-old female came to our surgery outpatient department with a chief complaint of a nodular mass in the left posterior aspect of her leg, 5 cm from the Achilles tendon. On fine-needle aspiration cytology, it showed deceptive atypical squamous cells that were reported as positive for malignancy – SCC. Wide local excision was done and reported as nodular hidradenoma with squamous differentiation. Any adnexal lesion suspected of malignant transformation on cytology needs to be evaluated for malignant transformation only after histopathology examination, along with immunohistochemistry, to make sure wide local excision is chosen, thereby preventing recurrence.