Malignant intracerebral nerve sheath tumor: A case report and review of the literature

BACKGROUND. Intraparenchymal nerve sheath tumors of the central nervous system are rare, usually benign tumors. Three cases with tumor recurrences have previously been reported in the literature. The authors report a case of a malignant intracerebral nerve sheath tumor in a gift age 8 years and analyze the biologic characteristics of this tumor. METHODS. The tumor was analyzed by histologic, immunohistochemical, and ultrastructural techniques. RESULTS. Magnetic resonance imaging revealed a mixed, attenuating, contrast- enhancing mass in the right posterior temporal lobe. Histopathology of the resected specimen revealed a uniformly S-100 positive and reticulin rich biphasic tumor with a characteristic distribution of spindle and epithelioid cells, with the latter almost entirely confined to the invading edge of the tumor. There was extensive brain infiltration in the form of lobules and fingerlike processes with a targetoid appearance. The spindle cells showed palisading and had elongated, wavy nuclei. Electron microscopy demonstrated basal lamina around both cell types with scattered Luse bodies in between. The patient is perfectly healthy and recurrence free 17 months after surgery. CONCLUSIONS. This represents the fourth and the youngest case in the literature of a malignant intracerebral nerve sheath tumor and highlights the distinctive clinicopathologic features of these tumors. First, these tumors have very great infiltrative potential, as observed histopathologically and reflected in their frequent recurrences. Second, epithelioid cells confined to the infiltrative edge suggest their aggressive role. Epithelioid cells have been shown to represent a malignant component of systemic schwannomas with malignant transformation; however, this case does not have any evidence of origin from a preexisting benign schwannoma. Third, despite histologic similarities to neuraxial desmoplastic neuroepithelial tumors, none of the malignant schwannomas had any evidence of divergent differentiation towards astrocytic or neuronal lineage, and had a much worse prognosis. Fourth, the event free survival after initial resection appears to be an important predictor of overall survival in the reviewed cases. Chemotherapy and radiation therapy have not been successful in the treatment of this rare entity. Hence, an accurate diagnosis and planned extensive resection appear to be the key elements in its management.