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The septum pellucidum (meaning translucent wall in Latin - SP), also known as the ventricle of Sylvius, is a thin, triangular double membrane separating the frontal horns of the right and left lateral ventricles of the brain. It extends between the anterior portion of the corpus callosum and the body of the fornix, and its width varies from 1.5 to 3.0 mm. The cavum septum pellucidum (CSP) is a potential cavity between the membranous leaves of the septum pellucidum, separated by at least 1 mm, and is considered a normal anatomical variation . It contains a filtrate of cerebrospinal fluid transferred from the ventricles through the septal laminae, and it does not communicate with the subarachnoid space. Sometimes, it may connect to a more posterior cavity called cavum vergae (CV), but separates from each other by an arbitrary vertical plane formed by the columns of the fornix. This activity reviews the cause and presentation of cavum septum pellucidum and stresses the importance of an interprofessional team in its management. Objectives: Describe the pathophysiology of cavum septum pellucidum. Review the necessary testing involved in the evaluation of a patient with cavum septum pellucidum. Summarize when treatment of cavum septum pellucidum is necessary, and describe the treatment and management. Explain the importance of interprofessional team strategies for improving care coordination and communication to aid in prompt diagnosis of cavum septum pellucidum and improving outcomes in patients diagnosed with the condition. Access free multiple choice questions on this topic.

The septum pellucidum (meaning translucent wall in Latin), also known as the ventricle of Sylvius, is a thin, triangular double membrane separating the frontal horns of the right and left lateral ventricles of the brain. It extends between the anterior portion of the corpus callosum and the body of the fornix, and its width varies from 1.5 to 3.0 mm The cavum septum pellucidum (CSP) is a potential cavity between the membranous leaves of the septum pellucidum, separated by at least 1 mm, and is considered a normal anatomical variation (see Images. Cavum Septum Pellucidum). It contains a filtrate of cerebrospinal fluid transferred from the ventricles through the septal laminae, and it does not communicate with the subarachnoid space. Sometimes, it may connect to a more posterior cavity called the cavum vergae, but it separates from it by an arbitrary vertical plane formed by the columns of the fornix. CSP and the cavum vergae were, respectively, incorrectly called the fifth and sixth ventricles in the past. Neither is part of the ventricular system, as they have different embryological origins and lack a lining of ependymal or choroid plexus cells. Boundaries of the septum pellucidum: Superiorly: Inferior surface of the body of the corpus callosum Anteroinferiorly: Superior surface of the genu of the corpus callosum Posteroinferiorly: Corpus and columns of the fornix Laterally: Medial wall of the frontal horns of the lateral ventricles Medially: Virtual space with the contralateral septum Boundaries of CSP: Anteriorly: Genu of the corpus callosum Superiorly: Body of the corpus callosum Posteriorly: Anterior limb and pillars of the fornix Inferiorly: Anterior commissure and the rostrum of the corpus callosum and Laterally: Leaflets of the septum pellucidum.[1] Septum pellucidum is an important part of the limbic system, with prominent connections to both the medial and the basolateral limbic circuit. Disease affecting the CSP can cause symptoms either by mass effect or by disruption of the limbic system's emotional and behavioral functions.

The septum pellucidum is formed embryologically by 2 closely opposed leaves enclosing a cavity called the CSP. The leaves of the septum pellucidum fuse in a caudal to the rostral direction at approximately 6 months of intrauterine life. The CSP cavity usually disappears by 3 months of postnatal life. However, if the gap is not closed, CSP may persist and can be seen even in adults.

CSP is estimated to occur in all premature infants, in 85% of full-term neonates, and 12% of children between 6 months and 16 years old. Eighty-five percent of CSP fuses around 3 to 6 months after birth.[2] In adults, the prevalence varies from 4 to 74%, depending on detection methods and anatomical definition. Cysts of CSP are rarer, with an incidence of 0.04%, as found by Wang et al, whereas symptomatic CSP cysts are very rare lesions with only a few cases described in the literature.[3]

CSP does not cause symptoms. Symptoms are more likely to occur with CSP cysts, though most of them are incidental findings. There are mainly 3 mechanisms described: Ball-valve phenomenon: Obstruction of the interventricular foramina by the cyst, leading to hydrocephalus and increased intracranial pressure. Compression of the hypothalamo-septal triangle: Compression of structures formed by the septal and periseptal nuclei and their associated projection pathways may lead to neuropsychiatric symptoms and compression of the optic chiasm and visual pathways. Chronic deep venous impairment: Displacement and stretching of the internal cerebral and subependymal veins may result in progressive focal neurologic deficits.[4] The CSP cavity may expand to form a CSP cyst, probably due to the ability to secrete fluid internally. The well-accepted definition of a CSP cyst is a cystic structure having a width of 10 mm or more in the septum's region, the walls of which exhibit lateral bowing.[5] There is no strict definition differentiating a large CSP from the CSP cyst. CSP cysts are classified into 2 categories: communicating and noncommunicating, depending on whether they communicate with the ventricles. A noncommunicating cyst may become communicating due to spontaneous rupture or during head trauma, diagnostic procedures (ventriculography and pneumoencephalography), or surgery. The reverse is also possible if fibrosis occurs at the site of communication. CSP cysts can also be classified as symptomatic or asymptomatic.

CSP has a lining of glial and neuronal cells.[6] The boxer’s cavum displayed a characteristic fenestration with the detachment of the fornix from the undersurface of the corpus callosum, with the 2 flattened forniceal bodies splaying out horizontally.[7]

Many symptoms and diseases have historically been attributed to cysts of the CSP - mental disturbances, ataxia, disordered speech, epilepsy, and bilateral pyramidal signs. But these are now being questioned because of a lack of proper evidence. CSP cysts may also cause acute or chronic headaches, papilledema, emesis, syncope, cognitive impairment, emotional and behavioral disturbances, and visual and sensorimotor findings.

Proper evaluation of CSP requires brain magnetic resonance imaging. In fetal life, visualization of the CSP between 18 and 20 weeks’ gestation indicates normal brain development.[8] Its assessment is a mandatory part of a second-trimester ultrasound. The absence of CSP is a marker of associated fetal anomalies (listed under complications).

Treatment indications for CSP are the following conditions: Association of a CSP cyst on imaging studies and clinical signs and symptoms because of the obstruction of the cerebrospinal fluid flow in the foramen of Monro Direct compression of the surrounding tissues by the cyst Mental status changes or focal neurological deficits attributable to the CSP cyst The primary goal of treatment is to relieve the mass effect caused by the cyst; it is surgical only. The classic treatment in these cases is surgical, including open procedures, conventional shunting, and stereotactic fenestration. Dandy published the first report of a treated CSP cyst in 1931; he treated a 4.5-year-old boy with a transcallosal fenestration.[9] Since 1995, when Jacowski et al described the first endoscopic approach, neuroendoscopic fenestration has become a well-established therapeutic option and is currently the treatment of choice for symptomatic CSP cysts.[10] Three endoscopic approaches are described: A frontal approach to the coronal suture 3 cm from the midline, targeting the frontal horn of the lateral ventricle (used by the majority of authors) The same cortical frontal approach, but directly targeting the cyst that is punctured, and then a fenestration of the 2 walls is performed An occipital burr hole to optimize the trajectory into the atrium of the lateral ventricle, which would allow an approach to both leaflets of the cyst perpendicularly.[11] The endoscopic fenestration offers a less invasive approach, direct visualization, and effectiveness. Direct visualization of neural and vascular structures prevents inadvertent injury. It is also important to inspect the foramina of Monro to look for potential adhesions, which may play a role in the persistence of hydrocephalus after apparently successful cyst drainage. Additionally, this technique avoids the need to place a shunt and allows cyst wall biopsy. The presence of CSP and cavum vergae may affect the choice of route for intracranial endoscopic surgery, with the transcavum interforniceal path preferred over the transforaminal approach into the third ventricle.[6]

The cavum vergae extends from the CSP posterior to the anterior columns of the fornix, lying anterior to the splenium of the corpus callosum (see Image. Cavum Vergae). The cavum veli interpositi extends from below the splenium of the corpus callosum and the column of the fornix and above the internal cerebral veins. Its shape is triangular, with the apex pointing anteriorly, reaching as far forward as the foramen of Munro Vein of Galen aneurysm - Diagnosed by color Doppler technology Arachnoid cyst Dilated third ventricle (distinguished by its location between the thalami)

Enlarged CSP is seen in the following conditions: Schizophrenia patients (First reported by De Greef) Aggressive individuals with an alcohol use disorder People with neurological development disorders Boxers due to repeated head trauma Post-traumatic stress disorder patients Military population currently participating in war conflicts or veterans of wars Obsessive-compulsive disorders [6][12][13][14] The absence of the CSP in fetal life correlates with the following conditions: Holoprosencephaly Septo-optic dysplasia Agenesis of the corpus callosum Alexander disease Tuberous sclerosis Phacomatosis Pinealoma Trisomy 21 Schizencephaly Lissencephaly Chiari malformation

Patients need reassurance that CSP is a normal anatomical variation and requires no surgical intervention and is unlikely to progress. Only if the size is >1 cm or if symptomatic does an enlarged CSP require further evaluation and management.

Symptomatic enlargement of the CSP is rare and most commonly causes intermittent obstructive hydrocephalus with headache and loss of consciousness. It is amenable to surgical treatment such as cyst puncture or shunting, ventriculoperitoneal shunting, or radical excision. CSP is an important marker for evaluating the normal development of the fetal neural axis.

A rigorous evaluation, including neurological and radiological examinations, is necessary before treatment. Hence, discussions with the radiologist, neurologist, and neuropsychiatrist are needed before proceeding with surgery for CSP cysts, even though they appear to be symptomatic.