The fine structure of hyaline inclusions in meningioma

Hyaline inclusions of three meningiomas were studied at the ultrastructural level. The inclusions apparently arise as the result of fusion of smaller microvillus-containing intracytoplasmic cysts. The content of the inclusions consists of finely reticulated filamentous material. These findings suggest a secretory differentiation of meningeal cells in these meningiomas.