[Electron-microscopic study of the arachnoid cyst (author's transl)].

The primary arachnoid cyst developed on the left middle cranial fossa of 5 year-old girl was examined with electron-microscope and discussed its pathogenesis. The cyst wall was mainly composed of two distinct layers, one was compact arranged flattened cells and others loosely arranged of collagen fibers and fibroblast. Various junctions were observed between those cells. Those features were similar to that was seen in normal arachnoid membrane. However, the abundant attenuated cell processes, whole formation and psammoma body were observed in cyst wall. Those finding suggested the cyst was congenital arachnoid malformation, resulting from abnormal proliferation of developing arachnoid cells.