[Pseudo-oligodendrogliomatous meningioma. Report of 2 cases and review of the literature].

We report two cases of oligodendroglioma-like meningioma revealed by symptoms of increased intracranial pressure, progressive hemiparesia and partial epileptic seizures. Brain CT-scan or scintigraphy and carotid arteriography were suggestive of a convexity meningioma. One patient had received radiation treatment for scalp tinea capitis 25 years previously. In spite of complete surgical removal, the tumor recurred in both cases respectively 17 years and 18 months later. The two patients were operated again, and one underwent a complementary radiotherapy. Pathologic diagnosis was particularly difficult in the first case where the pattern at conventional histologic technics was that of oligodendroglioma. On the occasion of recurrence, immuno-histochemistry and ultrastructural studies were performed. The tumor was positive for epithelial membrane antigen (E.M.A) and cytokeratin, but was negative for glial fibrillary acidic (G.F.A.) protein, S 100 protein (S 100), neuron-specific enolase (N.S.E.), vimentin, anti-LEU-7 (N.H.K.1), and neurofilaments (N.F.). Electron microscopy showed closely adjacent cells with tonofilaments and numerous desmosomes. These findings permitted to establish the diagnosis of oligodendroglioma-like meningioma instead of oligodendroglioma. In the second case, the histologic pattern was also reminiscent of oligodendroglioma, but presence of few cellular whorls in some part of the tumor permitted the correct diagnosis. The pathogenesis of this atypical form of meningioma, its tendency for recurrence, and usefulness of radiotherapy are discussed and literature is reviewed.