Superficial spreading malignant melanoma with neurosarcomatous metastasis.

Metastatic malignant melanoma often poses a difficult light and ultrastructural diagnostic challenge. A superficial spreading malignant melanoma without desmoplasia displayed neurosarcomatous light and electron microscopic features in metastatic sites. The ultrastructure displayed some Schwann cell features and strong-S-100 immunostaining. Metastatic melanoma with Schwannian differentiation in metastatic sites without lesional desmoplasia is rare and must be included in the differential diagnosis of spindled neoplasms involving lymph nodes. The evolution of this lesion illustrates the spectrum of melanocytic differentiation, i.e., pigment synthesis, adaptive fibroplasia and Schwannian differentiation.