Malignant Nodular Hidradenoma on the Scalp: Report of a Case with Fine Needle Aspiration Cytology Features and Histologic Correlation

Malignant nodular hidradenoma (MNH) is a malignant adnexal tumor of the eccrine sweat glands. The histology is similar to that of benign nodular hidradenoma, but MNH shows an infiltrative and invasive pattern, necrosis and angiolymphatic invasion. A 60-year-old woman, diagnosed with rectal adenocarcinoma 6 months before, underwent fine needle aspiration (FNA) of a nodule on the scalp. The aspirate smears showed (1) necrotic debris; (2) cohesive cell clusters and tissue fragments; (3) tubular formations; (4) globoid or cylindrical clear cells; (5) cells showing dense cytoplasm and a basaloid appearance; (6) cell sheets with anaplasia and squamous differentiation; and (7) multinucleated giant cells. The histology showed a lobulated pattern with necrosis and cyst formation. The clear cells that were seen on cytology occupied the periphery of the lobules, whereas the anaplastic cells were located in the central portion. Squamous differentiation and tubular formations were observed. Rapid, accurate diagnosis of these tumors is important, particularly when they develop at sites where a metastatic process must be ruled out. Cytology of FNA material provides this capability.