MICROCYSTIC-MENINGIOMA - TUMORS OF ARACHNOID CAP VS TRABECULAR CELLS

Three unusual meningiomas with extensive microcystic formation were st udied by light- and electron-microscopy. The tumor cells in the first and second cases had many morphological characteristics in common with the arachnoid cap cells: prominent and complex interdigitation of the fine cytoplasmic processes, numerous well developed desmosome attachm ents, and intracytoplasmic microfilaments. The prominent features of t hese tumors were a marked vascularization and hyaline thickening of th e vessel walls, and the microcystic formation was considered to be rel ated to these changes. In contrast, the tumor cells of the last case h ad characteristic structures in common with trabecular arachnoid cells . They were stellate in shape, and had only a small number of intracyt oplasmic filaments. Arborizing relatively thick and long cytoplasmic p rocesses showed simple junctions with occasional desmosomes, and delim itated microcysts. The tumor cells in this case were considered to rec apitulate the subarachnoid structure and formed microcysts. Although t he histogenesis of microcysts in meningiomas is not considered to be u niform, the biological behavior of these 3 tumors corresponded to thos e of meningiomas in general.