The Cavum Septum Pellucidum (CSP) is a small, fluid-filled space located deep within the center of the brain. While its identification on an imaging scan can cause concern, the CSP is usually a normal and temporary part of fetal brain development. In infants and young children, it is often an incidental finding that poses no threat to health. Understanding when the CSP is a typical developmental variant and when it signals a need for further investigation is essential.
The Structure and Expected Development of the CSP
The Cavum Septum Pellucidum is situated between the two lateral ventricles, separating the frontal horns. This space is enclosed by the thin, translucent double membrane known as the septum pellucidum, which stretches from the corpus callosum down to the fornix. The CSP is present in nearly all developing fetuses, forming a cerebrospinal fluid (CSF)-filled pocket between the two layers of the septum.
Its presence serves as an indicator of normal forebrain development during the prenatal period, and its visualization on a fetal ultrasound is a routine part of a second-trimester assessment. As the brain matures, the surrounding structures expand and press the two leaves of the septum pellucidum together, causing the space to fuse and disappear. This fusion typically occurs in a back-to-front direction.
For full-term neonates, the CSP is still present in about 85% of cases, but this number rapidly declines shortly after birth. The fusion process is generally complete within the first three to six months of life. The eventual closure is believed to be influenced by the growth of nearby brain structures, primarily the corpus callosum and the fornix.
When the Cavum Septum Pellucidum is Considered Persistent
A Cavum Septum Pellucidum is considered persistent if the two septal membranes fail to fuse and the cavity remains open past the typical closure period. Although the exact age threshold varies, persistence is generally defined as the CSP remaining open beyond six months to one year of age. This persistence is relatively common, appearing in approximately 15% of the adult population, and is often considered a benign anatomical variant.
The definition of persistence also includes the size and location of the cavity. A normal, persistent CSP is usually a small, slit-like space, typically measuring between 1 and 4 millimeters in length.
Other Cavum Variants
If the fluid-filled space extends further back beyond the columns of the fornix, it is termed a Cavum Vergae. If it is located above the third ventricle, it is called a Cavum Veli Interpositi.
The existence of a persistent CSP means the normal developmental fusion of the septal leaves did not occur. It is a structural finding that, in isolation, does not automatically imply neurological or developmental impairment. However, a persistent CSP can signal a need for closer observation, especially when it is unusually large or complex.
Potential Clinical Significance of a Persistent CSP
For most individuals, a persistent CSP is an incidental finding on a brain scan and is asymptomatic. This is particularly true for an isolated CSP that is small and does not exceed five millimeters in length. When the cavity is non-communicating and significantly enlarged, however, it can become a symptomatic “CSP cyst.”
A CSP is considered enlarged when its width is six millimeters or more, often causing the septal walls to bow laterally. In rare instances, a significantly enlarged cavity (a true CSP cyst) can obstruct the normal flow of cerebrospinal fluid. This obstruction leads to hydrocephalus and increased intracranial pressure. Symptoms can include persistent headaches, visual changes, or nausea.
Beyond physical obstruction, a persistent CSP is sometimes found in conjunction with other serious brain anomalies, pointing to a disruption in early brain development. These associated conditions include structural midline defects such as agenesis of the corpus callosum.
The CSP is also associated with certain neurodevelopmental and psychiatric disorders, such as schizophrenia and post-traumatic stress disorder, particularly when the cavity is complex or excessively large. These associations are debated and do not mean the CSP causes these disorders. Instead, a failure of the septum to close may be a marker for underlying developmental differences in the limbic system.
Monitoring and Management Following Identification
When a Cavum Septum Pellucidum is identified prenatally or in a young infant, medical professionals may recommend follow-up imaging to monitor the cavity. This tracking, often done with ultrasound or MRI, observes whether the CSP closes naturally or if its size increases. The primary concern is ruling out associated brain malformations that might require early intervention.
If a CSP is discovered in an older child or adult and is isolated, small, and asymptomatic, no specific treatment or intervention is necessary. The finding is noted as a benign anatomical variant. Management is only required if the CSP is symptomatic, usually due to its enlargement causing obstructive hydrocephalus.
For symptomatic CSP cysts, the treatment is typically surgical, with the goal of relieving pressure and restoring the normal flow of CSF. The most common procedure is neuroendoscopic fenestration, which involves creating a small opening in the cyst wall to allow the fluid to drain into the ventricular system. A neurologist or developmental specialist may be consulted to evaluate the individual for any associated neurodevelopmental or cognitive concerns if the CSP is complex or found alongside other anomalies.