A rare case of cutaneous pseudoglandular schwannoma.

Schwannomas are benign tumors that arise from the peripheral nerve sheath. Many variants of schwannomas exist, including plexiform, epithelioid, cellular, glandular, and ancient. The pseudoglandular subtype is extremely rare, as fewer than five cases of cutaneous pseudoglandular schwannomas have been reported based on our literature review. Herein, we report a case of a 64-year-old female who presented with a skin-colored nodule on her right arm for several years. Histopathology showed a superficial and deep dermal nodulocystic neoplasm composed of epithelioid and spindle cells surrounded by a fibrous stroma. The epithelioid cells surrounded multiple spaces suggestive of glandular differentiation, although many of these spaces also contained serum and red blood cells, raising consideration for vascular differentiation. Multiple epithelial markers, including pancytokeratin and epithelial membrane antigen, were all negative, providing no support for an epithelial tumor with true ductal/glandular differentiation. In addition, CD31, CD34, smooth muscle actin, and desmin stains were negative in these spaces, making a vascular neoplasm or smooth muscle tumor unlikely. However, SOX10 and S-100 stains were positive, including in cells lining the pseudoglandular spaces, supporting the diagnosis of pseudoglandular schwannoma. Complete excision was recommended. This case highlights an extremely rare presentation of the pseudoglandular variant of schwannoma.