Abstract

A 51-year-old male with no significant past medical history presented for further evaluation and management of a painless right groin mass that was noticed on self-examination and had been on-going for several months. An abdominopelvic CT scan revealed a 3 cm peripherally enhancing, well-circumscribed right inguinal mass superficial to and displacing the surrounding common femoral vessels. The clinical differential diagnosis included an enlarged lymph node, as well as inflammatory and neoplastic etiologies, including metastases. Surgical excision was performed, and histopathologic examination revealed a well-circumscribed epithelioid neoplasm involving a lymph node and composed of large, cuboidal, bland-appearing cells with prominent clear cell features and small round nuclei, growing in sheets. Metastatic hidradenocarcinoma was considered; however, no significant cytological atypia, necrosis, or mitotic activity was noted. Immunohistochemistry was performed to exclude the possibility of a metastatic renal cell carcinoma and revealed no staining of the neoplastic cells for PAX8 and RCC, focal luminal staining for CD10, and a low Ki67 proliferative index. The morphological and immunophenotypic findings were most consistent with a clear cell hidradenoma arising in a lymph node. The presentation of this benign cutaneous adnexal tumor associated with a lymph node is highly unusual, but has rarely been reported in the literature in case reports and limited small case series, with excellent prognosis. Awareness of this exceptionally rare presentation pattern among dermatopathologists is crucial to avoid misdiagnosis.

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