Microcystic meningioma. Clinicopathologic report of eight cases.

We report herein eight cases of microcystic meningiomas. This unusual variant was originally described by Masson, who labeled it "humid." Grossly, tumors were usually soft, with occasionally a glistening cut surface. Two tumors were cystic and three invaded bone structures. By light microscopy, tumor cells were stellate, with long processes delimitating clear spaces. Whorls were found in all tumors. Intracytoplasmic glycogen, fatty droplets, and phosphotungstic acid-hematoxylin-positive fibrils were sometimes seen. Tumor cells, however, were all negative with the peroxidase-antiperoxidase technique for glial fibrillary acidic protein. Mitoses, hemorrhages, and necrosis were absent. By electron microscopy, interdigitations of cytoplasmic processes and desmosomes were found. The large extracellular spaces were filled with a finely granular substance intermingled with fibrils and collagenic fibers. The clinical and morphological findings point toward a benign course. We also discuss the differential diagnosis and the pathogenesis.