Intradermal Nevus with Prominent Schwannian Differentiation

Summary: Melanocytes and Schwann cells share a common embryologic origin from the neural crest. Peripheral nerve sheath differentiation has been described in melanocytic nevi. We report a case of a predominantly intradermal nevus with prominent Schwannian differentiation. Histopathology revealed a polypoid lesion with epidermal thinning and effacement of rete ridges. The dermis had multiple nodules of nested melanocytes; epithelioid cytology predominated in the superficial and peripheral portions, while spindled melanocytes arranged in a palisaded pattern were present centrally. Both epithelioid and spindled cells lacked cytologic atypia and mitotic figures. Melan-A/Ki67 staining revealed absence of cell proliferation; Melan-A expression was strongest in the superficial and peripheral epithelioid cells, while the central spindled melanocytes showed weak Melan-A staining. HMB45 demonstrated maturation, with strong staining of melanocytes at the superficial and peripheral portions of the dermal nests, and weak staining of the central spindled melanocytes. BAP1 and p16 exhibited retained nuclear staining throughout the lesion. Prominent Schwannian features present in this intradermal nevus underscores the close developmental relationship between melanocytes and Schwann cells, likely derived from shared precursor cells. This case illustrates the essential role of immunohistochemistry in accurately differentiating between melanocytic and neural tumors, particularly when dual features coexist in a single lesion.