Cave of septum pellucidum

Cave of septum pellucidum
Stylized horizontal section through the brain showing normal and cave of septum pellucidum.
Difference between cave of septum pellucidum (CSP), cavum vergae (CV), and cavum veli interpositi (CVI). 3=third ventricle, 4=fourth ventricle.
Details
Identifiers
Latin	Cavum septi pellucidi
TA	A14.1.09.263
FMA	61874
Anatomical terms of neuroanatomy []

The cave of septum pellucidum (CSP), or cavum septi pellucidi, describes a slit-like space in the septum pellucidum. The septum pellucidum is a laminated thin translucent vertical membrane in the midline of the brain separating the anterior horns of the right and left ventricles. It lies posterior to the corpus callosum. In fetal life the laminae of the septum pellucidum separate to form a small cavity – the cavum septi pellucidi. This is an important normal structure to identify in the sonographic assessment of the fetal brain. In post-natal life the laminae of the septum pellucidum usually fuse which obliterates the cavum. The cavity contains cerebrospinal fluid (CSF) that filters from the ventricles through the septal laminae.

The cave of septum pellucidum is bounded anteriorly by the genu of the corpus callosum; superiorly by the body of the corpus callosum; posteriorly by the anterior limb and pillars of the fornix; inferiorly by the anterior commissure and the rostrum of the corpus callosum; and laterally by the leaflets of the septum pellucidum.

There are individual differences in the degree of CSP; whereas some have complete closure of the cavum, others present with a small degree (4-6mm in the coronal plane) of incomplete closure.

The most common type of CSP is noncommunicating, that is, it does not connect to the brain's ventricular system. Because of this lack of communication, the erstwhile term for CSP, the "fifth ventricle," is not anatomically correct and its use has fallen out of favor in recent years.

CSP is present in 100% of fetuses, but over 85% of them fuse by 3–6 months after birth.

The cause of CSP is basically unknown, although it is thought that prenatal alcohol exposure plays a significant role.

CSP is a marker for fetal neural maldevelopment. The septum pellucidum is a thin, triangular, vertical membrane separating the anterior horns of the left and right lateral ventricles of the brain. It runs as a sheet from the corpus callosum down to the fornix. During fetal development at approximately the twelfth week of gestation, a space forms between two laminae, which is the CSP. At approximately the twentieth week of gestation, the laminae start to close. This closure ends shortly after birth (3–6 months postnatally). Fusion of the CSP is attributed to rapid development of the alvei of the hippocampus, amygdala, septal nuclei, fornix, corpus callosum and other midline structures. Lack of such limbic development interrupts this posterior-to-anterior fusion, resulting in preservation of the CSP into adulthood.