Intracellular inclusions in meningothelial meningioma. A histochemical and ultrastructural study.

This is a study on the histochemical and electron microscope findings of the intracellular inclusions in a case of meningothelial meningioma of the frontoethmoidal region with orbital involvement. The inclusions are PAS-positive, diastase resistant, and stain strongly positive with the modified Morel-Sisley reaction for protein-bound tyrosine and weakly with dihydroxy-dinaphthyl-disulfide (DDD) for the demonstration of sulfhydryl (SH) and disulfide (S-S) groups of proteins. These staining reactions suggest the inclusions are composed of conjugated proteins (glycoproteins). Ultrastructurally, the inclusions are located within intracellular spaces lined by microvilli and are composed of granular material, usually forming a dense core that is intermixed with small vacuoles. Numerous desmosomes and whorls of tonofibrils are concentrated around them. Our findings support the view that the intracellular inclusions, which are rarely found in meningiomas, represent an active secretory product of the meningothelial cells rather than a degenerative or phagocytic process.