Primary meningeal sarcomas with leiomyoblastic differentiation - A proposal for a new subtype of primary meningeal sarcomas

Two cases of primary meningeal sarcoma with leiomyoblastic differentiation are presented. In case no. 1, the tumor showed anaplastic spindle cell tumo r components intermingled with anaplastic meningothelial components. Mening othelial tumor cells gradually became transformed into spindle tumor cells. Spindle tumor cells reacted with antisera to muscle actin (HHF-35) and alp ha-smooth muscle actin. However, unchanged meningothelial tumor cells did n ot react with the antisera to HHF-35 and alpha-smooth muscle actin. Electro n microscopy showed condensations of cytoplasmic fibers and pinocytotic ves icles in spindle tumor cells similar to those seen in smooth muscle cells. In case no. 2, the tumor cells consisted predominantly of sheets of round o r polygonal cells as seen in an epithelioid leiomyosarcoma. The neoplastic cells had frequent nuclear inclusions, such as those seen in meningiomas. I mmunohistochemically, the tumor cells reacted with antisera to desmin and t o HHF-35. Electron microscopy showed a basal lamina around the cytoplasm of tumor cells. Intranuclear inclusions with various cytoplasmic organelles w ere frequently observed in the tumor cells, as in meningiomas. Interdigitat ing cytoplasmic processes and intercellular junctional complexes, however, were not found in the tumor cells. Two possible hypotheses explain the occu rrence of leiomyoblastic characteristics of these cases. In case no. 1, lei omyoblastic cells originated from meningothelial cells with the advancement of meningothelial anaplasia. Tn case no. 2, pluripotential mesenchymal cel ls in the meninges differentiated into meningothelial and smooth-muscle cel l lines at the time of tumor growth. With consideration of previous publica tions on primary meningeal sarcoma, these cases are the first reported prim ary meningeal sarcoma with leiomyoblastic and meningothelial differentiatio n.