Septum pellucidum

The septum pellucidum is a thin, triangular, double-layered membrane situated in the midline between the frontal horns of the right and left lateral ventricles. It extends between the corpus callosum superiorly and anteriorly and the fornix posteroinferiorly. Its thickness is approximately 1.5–3 mm.

Relations

The principal relations of septum pellucidum are:

• Superiorly: inferior surface of the body of the corpus callosum

• Anteroinferiorly: genu of the corpus callosum

• Posteroinferiorly: body and columns of the fornix

• Laterally: frontal horns of the lateral ventricles

• Medially: the opposing septal leaflet.

The two leaflets may enclose a potential midline space called the cavum septi pellucidi (CSP). It contains fluid similar to cerebrospinal fluid but is not part of the ventricular system, because it lacks an ependymal or choroid plexus lining and normally does not communicate with either the ventricles or subarachnoid space. Posteriorly, it may be continuous with the cavum vergae; neither cavity should be regarded as a true ventricle.