A Rare Case of Cutaneous Oncocytic Hidradenoma

Abstract

Oncocytes are epithelial cells characterized by their abundant eosinophilic and finely granular cytoplasm. Their histologic appearance is due to excessive amounts of cytoplasmic mitochondria. Oncocytes generally occur in the setting of benign neoplasms. Oncocytomas, or tumors composed primarily of oncocytes, are typically found in the kidneys. Other common sites include the salivary, thyroid, and parathyroid glands. Oncocytic metaplasia has only been rarely reported in various cutaneous neoplasms. We report a case of an elderly male presenting with a 5 millimeter erythematous papule on his left scalp, who underwent a shave biopsy showing a nodular, dermal-based adnexal tumor with prominent ductal differentiation, composed of multiple small, well-formed lumina surrounded by enlarged, bland-appearing epithelioid cells. CK7, EMA, and mCEA immunohistochemical stains were positive, consistent with adnexal differentiation. PTAH and LFB stains highlighted the cytoplasmic granules, consistent with mitochondria. The overall findings were consistent with oncocytic nodular hidradenoma. Oncocytic hidradenoma is a very rare entity, with only 1 previously reported case in the literature.

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