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Case Reports

Abstract

Epithelioid schwannoma is a rare subtype of benign nerve sheath tumor first described by Stewart and Copeland in 1931. It is more likely to be encapsulated and lacks the classic Antoni A and B areas which, in combination with the epithelioid morphology, may make diagnosis challenging. Often, adjacent foci of classic schwannoma provide an important clue. Epithelioid schwannomas exhibiting clear cell morphology have been reported only rarely. Herein we present a novel case of cutaneous epithelioid schwannoma with clear cell change, which lacked adjacent areas of conventional schwannoma, and presented a diagnostic conundrum. A 63-year-old man presented with a one-year history of a growing subcutaneous nodule in the popliteal skin. Gross examination was significant for a 1 cm pink-tan crusted lesion. Histologic examination revealed a well-circumscribed, encapsulated, solid and cystic neoplasm with ulceration and extension into the subcutaneous tissue. The neoplasm consisted of nests, cords, and large sheets of pleomorphic epithelioid cells with abundant amounts of clear to eosinophilic cytoplasm and scattered hyalinized blood vessels. The tumor cells were diffusely positive for SOX10 and S100, and negative for a battery of other stains including keratins, HMB45, Melan-A, PRAME, and other cell lineage markers. The EMA and GLUT-1 stains highlighted perineurial cells in the capsule, helping confirm the diagnosis of epithelioid schwannoma. Clear cell epithelioid schwannoma must be differentiated from melanoma and epithelioid mesenchymal neoplasms, including ballon cell melanoma, clear cell sarcoma, and epithelioid malignant peripheral nerve sheath tumor. Demonstration of perineurial cells in the capsule can assist the differential diagnosis.