The septum pellucidum is one of the septa dividing the right and left lateral ventricles and consists of two triangular shaped glial membranes. Normally these two membranes will fit tightly together, and some patients have an underlying cavity between the two membranes called the septal interstitial cavity or fifth ventricle. In some patients, this intercompartmental cavity is still found after examination in adulthood. If fluid accumulates in the intercompartmental cavity and there is excess cerebrospinal fluid, a septal cyst may form. The hyaline septal cavity and hyaline septal cyst are growth abnormalities that do not cause clinical symptoms and often this abnormal structure is discovered accidentally during a physical examination. If the cysts progressively increase in size, they may compress the surrounding brain tissue and produce an occupying effect, requiring a neurosurgical visit and, if necessary, surgical management can be considered.