Malignant Schwannoma associated with von Recklinghausen's neurofibromatosis.

A series of 46 malignant schwannomas occurring in soft parts of patients having von Recklinghausen's neurofibromatosis was analyzed. The diagnosis of malignant schwannoma was based upon the occurrence of malignant spindled cells closely resembling Schwann cells in the neoplasm and the close association or origin of the malignant schwannoma in a neurofibroma (27 tumors), or a large peripheral nerve (31 tumors). Additional histologic features useful in making the diagnosis of malignant schwannoma included the arrangement of the spindled tumor cells in a whorled pattern about thin-walled, gaping blood vessels, perivascular cellular proliferation and the presence of prominent myxoid stroma containing abundant hyaluronidase-sensitive acid mucopolysaccharides. Nuclear palisading was present in only one case. Eight tumors containing both neoplastic Schwann cells and rhabdomyoblasts and five containing both neoplastic Schwann cells and rhabdomyoblasts (malignant "Triton" tumors) and five containing foci of malignant cartilage cells were included in the series. The neoplasms occurred principally in adults (median age, 34 years) and were most common in the lower extremity (18 cases) and retroperitoneum (11 cases). A mass with or without pain was the most common presenting symptom (28 cases). The median size of excised tumors was 11 cm. The malignant schwannomas were highly malignant neoplasms, causing the death of 39 patients within five years and two patients within 6--10 years after diagnosis. Only four patients were alive and free of tumor 5--15 years after diagnosis.