Neuroepithelial (colloid) cysts of the septum pellucidum.

The authors present two cases of neuroepithelial (colloid) cysts found above the diencephalic roof, occupying the space between the two fornices and the two leaves of the septum pellucidum, and describe the clinical history, neurological, and neuroradiological findings. Both lesions were removed through a right transventricular-transseptal approach. No other report of such a lesion in this location could be found in the review of literature. The pathogenesis of these cysts, both above and below the diencephalic roof, is discussed in light of the developmental anatomy of the area under consideration. In view of their origin from the neuroepithelium in the diencephalic roof, whether by a process of invagination into the third ventricle or by evagination into the velum interpositum, the so-called colloid cysts are more appropriately termed neuroepithelial cysts.