Intracytoplasmic Lumina in Meningioma: An Ultrastructural and Immunohistological Study

Abstract

Three surgically removed meningotheliomatous meningiomas with hyaline inclusions or pseudopsammoma bodies were studied. Ultrastructurally, the lumina seemed to be predominantly intracytoplasmic, defined by a systemic unit membrane; they displayed abundant microvilli and contained granular or filamentous material, vacuoles, vesicular bodies, and lamellar structures. The cytoplasm surrounding the intracytoplasmic lumina was electron-dense and contained tonofilments and desmosomal junctions. All three meningiomas showed expression of carcinoembryonic antigen, cytokeratin, and epithelial membrane antigen in the cells surrounding the hyaline bodies. Keratin, α-1-antitrypsin, and immunoglobulin M showed weak positive staining. There was widespread vimentin except in the cells with hyaline inclusions. Glial fibrillary acidic protein and S₁₀₀ were negative. These results provide additional confirmation of immunohistochemical data that can serve as evidence for epithelial and secretory differentiation in meningiomas.