Secretory meningiomas: immunohistochemical pattern of lectin and ultrastructure of pseudopsammoma bodies.
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 structure. The cytoplasm surrounding the intracytoplasmic lumina was electron-dense and contained tonofilaments and desmosomal junctions. All three meningiomas showed expression of carcinoembryonic antigen, cytokeratin, and epithelial membrane antigen in the cells surrounding the hyaline bodies. Keratin, alpha-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.