Myofibroblastic sarcoma in meningioma: a new variant of "metaplastic" meningioma.

The authors describe a mixed malignant dural tumor composed of meningioma and myofibroblastic sarcoma (MFS). The meningioma component displayed epithelial membrane immunoreactivity and interdigitating cellular processes with desmosomal junctions on electron microscopy. MFS cells were immunoreactive for smooth muscle actin and vimentin, and focally for factor XIIIa, CD31, CD34, and Ulex europeus lectin receptors. Electron microscopy showed collections of intermediate filaments, stress fibers, subsarcolemmal densities of microfilaments, occasional fibronexus fibrils, few pinocytic vesicles, and discontinuous external lamina. After gross total removal, the tumor recurred 1 year later as aggressive MFS only. Development of MFS in continuity with meningioma suggests induction of MFS by meningioma or a divergent differentiation of precursor of the neoplastic arachnoid cell.