A normal anatomical variation.
The potential cisternal space, containing Csf.
Triangular in shape with a wide base dorsally.
Located superior to the pineal gland, its boundaries are corpus callosum superiorly, tela choroidea inferiorly and the crus of the fornix on each side laterally.
Embryologically a part of the normal developing mid line structures of brain.
Seen at all ages, as an incidental finding, incidence decreases with age.