Walsh & Hoyt: Cysts of the Septum Pellucidum

Cysts located between the two laminae of the septum pellucidum occasionally occur as developmental anomalies. These cysts may be of two types: (a) incidental asymptomatic cysts that communicate with the ventricular system and (b) noncommunicating cysts that may become symptomatic as they increase in size. Hughes et al. observed that in some cases, the cyst or ""cave"" is lined by cells resembling ependymal cells but without cilia. Dandy termed this type of cave the ""fifth ventricle"" when it was anterior to the fornix and the ""sixth ventricle"" when it was posterior. In fact, three types of cysts occur in the region of the septum pellucidum.