Vacuolated (Microcystic) Meningioma

Abstract

Two patients with extensively vacuolated meningiomas are described. The first, a 51-year-old female who had had several convulsive seizures within a 3-month period, was found on a plain computed tomography (CT) to have a diffuse, hypodense lesion in the frontoparietotemporal region. Contrast enhancement was slight. Neuroradiological examination suggested an extra-axial mass lesion. Histopathological examination of the surgical specimen showed extensive vacuolation and meningothelial cell nests, and a diagnosis of meningioma was established. No lipids were demonstrated in the vacuolated component. Electron microscopy of a formalin-fixed specimen showed interdigitations of cytoplasmic processes and desmosomes. Cytoplasmic processes also delimitated intercellular spaces of variable size. The second patient, a 68-year-old female, had had several right facial spasms within 6 months before admission. Plain CT revealed a hypodense lesion in the left frontotemporal region. Enhanced CT showed a well defined mass lesion. Light microscopy of the tumor specimen showed an area of mixed vacuolated and angiomatous components. It is important to note that the CT appearance of such hypodense meningiomas may mimic that of intra-axial tumors, such as filial tumors. The low density is considered to be due to extensive, diffuse vacuolation. Electron microscopic findings suggest that one of the causes of vacuolation in vacuolated meningioma is recapitulation of the subarachnoid structure.