Epithelioid psammomatous melanotic schwannoma with osseous metaplasia.

Psammomatous melanotic schwannoma is a very rare soft tissue neoplasm, which is clinically, biologically, and histologically distinct from conventional schwannoma. A significant proportion of patients may present with Carney's heritable complex of myxomas, spotty pigmentation, and endocrine overactivity. Typically, the lesion is composed of spindled and epithelioid cells displaying abundant intracytoplasmic melanin pigment, together with the formation of psammoma bodies. We report an epithelioid example of this tumor arising in the anterior abdominal wall of a 23-year-old man. A unique feature was a peripheral rim of osseous metaplasia. The tumor was erroneously diagnosed as a metastatic malignant melanoma on initial examination owing to its immunohistochemical coexpression of S100 protein and HMB-45. Psammoma bodies have not to our knowledge been described in melanomas, and their presence serves as a useful clue to the diagnosis of psammomatous melanotic schwannoma.