(also called the septum Pellucidum), and not to be confused with the medial septum, is a thin, triangular, vertical membrane separating the anterior horns of the left and right lateral ventricles of the brain.
The septum pellucidum consists of two laminae of both white and gray matter. During fetal development, there is a space between the two laminae called the cavum septum pellucidum, which disappears during infancy in most individuals.
Liss and Mervis 1) described three variations of the septum pellucidum. The first variation (50%) is the single midline membrane with an ependymal lining on each ventricular surface. The second variation (25%) consists of two separate but closely apposed leaves that delineate a potential space. The third variation (25%) is the cavum septum pellucidum in which the leaves of the septum are visibly separated by a space of variable size. Congenital perforations of the septum pellucidum may be present in any of these variations. These perforations characteristically have smooth margins and may be single or multiple 2).