Solid and Cystic Hidradenoma of the Forearm: A Case Report.

A 41-year-old woman presented with a two-year history of a gradually enlarging, tender nodule on the left forearm. Ultrasonography revealed a subcutaneous mass with both solid and cystic components. The lesion was surgically excised in its entirety with local flap closure, and the postoperative course was uneventful. Pathological evaluation confirmed a solid-cystic hidradenoma, a rare tumor of sweat gland origin. While the coexistence of solid and cystic components is an inherent, defining feature of this tumor subtype rather than an atypical finding, this case is notable for its occurrence on the volar forearm, a site with very few comparable adult cases in the published literature. Because hidradenoma is easily mistaken for more common and, in the case of dermatofibrosarcoma protuberans, potentially malignant, cutaneous lesions, recognizing this diagnosis at atypical sites has direct implications for surgical planning and patient counseling. We present this case to contribute to the limited literature on adult extremity hidradenomas and to reinforce the value of including hidradenoma in the differential diagnosis of nodular cutaneous lesions arising outside its typical head, neck, and trunk distribution.