The ventriculus terminalis (VT) is a small ependyma-lined cavity within the conus medullaris that is in direct continuity with the central canal of the anterior portion of the spinal cord. Normally, such a cavity is identifiable only histologically in children and adults and can be visualized using common neuroradiological techniques only after dilation. Currently, the mechanisms of isolated dilation are not documented. The present work describes 2 cases of VT in elderly patients. Data from a histological and ultrastructural study of a case of VT dilation are reported, and the results are compared with those obtained from the VT of 5 fetuses to explain the nosological aspects of nontumoral VT lesions. Our data suggest that the site, age, and histological characteristics of the lesion allow us to define VT dilation as a nosological entity distinct from other cystic dilations of the conus medullaris.