Vacuolated meningioma. A light and electron microscopic study.

Two unusual cases of meningioma with extensive vacuolization have been studied by light and electron microscopy. There were two kinds of vacuoles in the tumor cells which had the characteristic ultrastructure of meningioma as well. The smaller intracytoplasmic vacuoles were lipid droplets, while the larger, more prominent vacuoles were found to be extracellular spaces probably containing plasmatic fluid. The tumor cells were very much stellate with extremely thin and long cytoplasmic processes having desmosome junctions and forming cavernous intercellular spaces, some of which contained collagen fibers and fibrils. Although the xanthomatous change has been well known, the latter features provide a resonable interpretation for the histology of the present tumors and fat-negative vacuoles in the ordinary meningiomas. The picture may be recapitulation of the subarachnoid structure. Furthermore, recognition of this type of meningioma is practically important especially in frozen section diagnosis not to misinterpret the tumor as liposarcoma, chordoma or metastatic adenocarcinoma.