[Electron microscopic study of hyaline inclusions in meningioma (author's transl)]

Three cases of meningioma showing hyaline-like inclusions by light microscopy were studied at the fine structural level. The hyaline-like inclusions were found to be cyst-like contents of variable size filled with moderately dense finely filamentous material arranged either in a reticulated configuration or closely packed and appearing relatively homogeneous and dense. The surrounding cyst membrane is characterized, especially in the smaller inclusions, by the presence of microvilli. The reticulated material is found at the inner aspect of the cyst membrane and is attached to it. It is identical to the coating material seen at the surface of various epithelia. In addition to the filamentous material, minute membrane-bounded vesicles are often found floating within the larger cysts. The inclusions apparently begin as small, microvillous-filled cysts which eventually cluster and presumably fuse to form a single large body.