Abstract

Apocrine hidrocystoma (AH), and apocrine cystadenoma (AC) exist as a spectrum of benign sweat gland neoplasms. These lesions can appear anywhere on the body but have predilection for head and neck, especially the scalp. Apocrine tubular adenosis in association with AH and AC has rarely been reported in literature. We present a case of a 42-year-old male with no significant past medical history who presented with a stable large fluid-filled cystic lesion (3.0 x 3.0) of the left parietal scalp. Surgical excision was performed under local anesthesia followed by wound closure with local tissue rearrangement. During surgery, the cystic mass ruptured and expressed brownish-black fluid. Gross examination of the surgical specimen revealed a cystic cavity with a smooth lining. Microscopic examination revealed a multiloculated cystic tumor in the dermis and subcutis with a double layered lining consisting of an inner columnar cell layer with bland basal nuclei and decapitation secretion and an outer layer of flattened myoepithelium. Areas of pseuopapillary projections and tubular growth were seen. Multifocal aggregates of small tubules lined by similar epithelium were seen outside the cyst wall within adjacent and intervening fibrous stroma. This finding initially raised concern for apocrine cystadenocarcinoma; however, the confinement of these small tubules to surrounding fibrous stroma, the absence of cytologic atypia and presence of myoepithelial cells confirmed with SMA and p63 immunostains are supportive of apocrine tubular adenosis. This case highlights the importance of recognizing this benign entity to avoid over diagnosing infiltrative growth in an otherwise benign adnexal neoplasm.

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