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Abstract

Epithelioid schwannoma is a rare, diagnostically challenging variant of schwannoma that can appear morphologically similar to other benign and malignant soft tissue tumors. We report a case of a 50-year-old female with a 1.2 cm nodule in the left thigh. The excised lesion was a well-circumscribed, dermal-based tumor with a thick fibrous capsule. Histologically, it was composed of clusters and cords of epithelioid cells embedded in a highly myxoid stroma with reticular and microcystic areas. The tumor cells had uniform oval to round nuclei with minimal pleomorphism and rare mitoses. The combination of cord-like growth pattern and abundant myxoid stroma raised a differential diagnosis of chordoma, myoepithelioma (parachordoma pattern), extraskeletal myxoid chondrosarcoma, and epithelioid schwannoma with myxoid change. Immunohistochemical staining showed diffuse positivity for S100 and SOX10 but negative staining for EMA, p63, desmin, CK903, CK7, CK5/6, CAM 5.2, pancytokeratin, brachyury, calponin, and MART-1. Collagen IV highlighted abundant basement membrane material surrounding individual tumor cells. The Ki-67 proliferative index was low. Fluorescence in situ hybridization (FISH) was negative for EWSR1 gene rearrangement. The combined morphologic, immunophenotypic, and molecular features supported the diagnosis of a benign epithelioid schwannoma with myxoid change. This case highlights the unique histologic features of a rare schwannoma variant complicated by abundant myxoid stroma and the critical role of thorough histopathologic and immunohistochemical workup in distinguishing it from other benign and malignant entities.