ABSTRACT
Non-neoplastic epithelial cysts resembling the neuroepithelial cysts of the IV ventricle have also been described outside of the ventricular cavities, either within the brain and spinal cord parenchyma (Friede and Yasargil, 1977; Shuangshoti et al., 1988; Kumar et al., 2001; Saito et al., 2005) or in the subarachnoid space (Tandon et al., 1972; Ho and Chason, 1987). In all of these cases, the lining of the cyst is composed of a single layer of columnar or cuboidal cells supported by gliotic tissue, sometimes with an intervening thin collagen membrane. No age or gender predilection has been noted (Shuangshoti et al., 1988). Despite the fact that extraventricular ependymal cysts can reach considerable volume, most of them are asymptomatic and present as incidental neuroradiological or autopsy findings (Gherardi, 1984). However, an occasional lesion may present with mass effect, seizures, or, rarely, with movement disorders (Shuangshoti et al., 1988; Goh and Maguire, 1996). The development of the extraventricular cyst has been reported by various authors as being attributed to either the ectopic displacement of segments of the neural tube wall or to leptomeningeal neuroglial heterotopia.
