Endoscopic Treatment of Symptomatic Septum Pellucidum Cyst in an Adult Patient—Case Report and Technical Notes

Abstract

Background: Midline cysts of the brain are comprised of the following entities, septum pellucidum cysts, cavum vergae cysts and velum interpositum cysts. These lesions are uncommon and often asymptomatic; nonetheless, certain clinical manifestations may be linked to midline cysts, including headaches, signs of elevated intracranial pressure, neurological deficits, or alterations in mental status. Controversy persists in the therapy of symptomatic cases, mostly due to the challenge of establishing a correlation between the symptomatology and the presence of the cyst. Case description: We present the case of a 64-year-old female known with type—1 neurofibromatosis that associated a midline cyst. The cyst was treated endoscopically, in the initial stage (single wall perforation) showed no clinical or imagistic improvement. The incriminated symptoms in these cases are caused not only by compression or obstruction of the CSF flow but also to a complex alteration of CSF dynamics, in this case the stoma was found permeable at the second surgery but there was no obvious communication on the preoperative evaluation by ventriculocisternostomy. A second surgery was performed, with bilateral perforation and subsequent improvement of symptomatology and decrease of cyst dimensions. A literature review is presented concerning clinical presentation, therapeutic options, and possible outcomes. Conclusions: Endoscopic fenestration is an efficacious method for treating midline cysts, with bilateral wall fenestration representing the standard practice. Understanding the anatomical and developmental specifics of the septal region, together with cerebrospinal fluid dynamics, is essential for effective treatment of this condition.

1. Introduction

The septum pellucidum is a two leaflet structure located between the fornix and the rostrum, body and genu of the corpus callosum [1]. The cavum septum pellucidum (CSP), cavum vergae (CV), and cavum velum interpositum (CVI) are either chronic or acquired midline abnormalities of the central nervous system [2] and consist in a fluid collection between the two leaflets. The presence of CSP is a common finding in newborns, frequencies of 85% being reported in this group [3], gradually disappearing during infancy to reach a frequency of about 15% in adult population [4].

A cyst of the septum pellucidum is defined as a liquid collection between the lateral ventricles whose walls exhibit lateral bowing and are larger than 1 cm [5]. The cysts are named according to the locations as: cyst of the septum pellucidum for lesions located anteriorly, cysts of the cavum vergae for lesions located posteriorly and cyst of the velum interpositum for those located inferiorly [2]. These cystic lesions are rare, with a prevalence of about 0.04% on imagistic studies, according to Wang [6]. Symptomatic cysts may cause different disorders that vary from headache to signs of hydrocephaly with vomiting and loss of consciousness [2] and even psychiatric disorders [7,8]. In the absence of symptomatology the clinical significance of these lesions remain unclear.

2. Case Report

A 64-year-old woman with a prior diagnosis of NF-1 was referred to our neurosurgical department with a history of intermittent occipital headache accompanied by episodes of nausea and vomiting. The episodes spontaneously resolve within hours after bed rest.

Neurological exam including fundoscopy was unremarkable, the physical exam revealed: café au lait spots, axillary freckles and neurofibromas (Figure 1).

Psychological exam showeds fixation hypomnesia with a MMSE score of 26/30, a digit span test of 4 for forward and 4 for reverse and mnesic retention with reproduction at 15 min of 5/10.

Imagistic exams, magnetic resonance imaging (MRI) revealed a large cyst of the velum interpositum measuring 2.47 cm in width and exhibiting lateral bowing against the lateral ventricles, (Figure 2) the cyst content being isointense with CSF. The ventricles were slightly enlarged, Evans index equal 0.3, but with no signs of active hydrocephaly.

The patient was positioned supine with the head slightly flexed. The entry point was settled on the right side, at 3.5 cm from the midline in front of the coronal suture. The ventricle was punctured at 4 cm from the bone and a 30⁰ angled rigid endoscope (KarlStorz GmbH & Co, Tuttlingen, Germany) was inserted in the frontal horn of the right ventricle. Once in, the normal anatomy of the ventricular system was identified (foramen of Monro, fornix, choroid plexus, anterior septal vein), then he endoscope was turned counterclockwise and the cyst wall was identified and perforated in a translucent avascular area, above and posteriorly to the foramen of Monro. The orifice was dilated using a 3F Fogarthy balloon and a second hole was performed above a septal vessel, and the cavity of the cyst was inspected. The patency of the dilated stoma was checked and the endoscope was retreated (movie 1).

The postoperative course was uneventful.

At 3 months the patient presented the recurrence of the symptomatology and the control MRI showed the same aspect of the cyst (Figure 2A,B). Given that, we decided to check the patency of the communication between the cyst and the ventricular system. We performed a CT ventriculocystenography which showed abnormalities in the CSF dynamics: first of all it was a delay of contrast reaching the ventricular system (presence at the level of basal cisterns but not at the level of the ventricles—acquisition at 15 min) and finally at delayed scan, 35 min after the injection, we observed the abundant presence of the contrast medium in the subarachnoid space and ventricular system but not at the level of the cyst. (Figure 3C,D). We assumed closure of the stoma and decided on a second surgery with the aim of performing the perforation of both cystic walls.

A second burr hole was performed more laterally (at 6 cm from the midline) in order to have the appropriate angle to fenestrate both walls of the cyst. Intraoperatively, surprisingly the stoma from the first intervention was patent (Figure 4), and we completed the surgery with the enlargement of the previous stoma and the perforation of the contralateral wall of the cyst (movie 2).

At 2 months the patient showed clinical improvement with resolution of headaches, and the MRI showed a decrease in the cyst volume compared with the preoperative exam and also a decrease of the ventricles (Evans index equal 0.27) (Figure 5).

3. Discussions

The septum pellucidum is a bilayered structure, including gray and white matter, situated between the genu of the corpus callosum anteriorly, the body of the corpus callosum dorsally, the fornix posteroventrally, and the lateral ventricles laterally [2].

Cavum septum pellucidum and cavum vergae are midline are fluid filled structures, between the leaflets of the septum pellucidum [1]. Collections larger than 1 cm are considered cysts, the term giant being reserved for lesions larger than 4 cm [2].

The existence of a cavum septum pellucidum signifies a typical anatomical variant that is generally asymptomatic. The incidence in children diminishes with age, observed at necropsy in all preterm infants, 85% of one-month-old infants, and 12–15% of six months old infants and gradually disappearing during infancy to reach a frequency of about 15% in adult population [4,9].

The velum interpositum space is the arachnoid space situated between the fornices and their corresponding choroid plexus, as well as the choroid that constitutes the inferior ceiling of the third ventricle [10]. The cavum veli interpositi is a cavity created by the pia mater fold (tela choroidea) during the interhemispheric separation associated with the development of the corpus callosum, situated within the transverse cerebral fissure (choroid fissure). It denotes a prospective cisternal area harboring cerebrospinal fluid between the internal cerebral veins and the posterior medial choroidal artery [11]. Cysts of the velum interpositum will have a particular MRI image, showing on axial images a distinct triangular appearance with an apex oriented anteriorly and on coronal images, large cysts will displace the cerebral veins inferiorly and laterally [10].

3.1. Cavum Vergae

Cavum vergae is a posterior extension of the cavum septum pellucidum, extending beyond the columns of the fornix and the foramen of Monro. This structure is observed in up to 30% of neonates but remains in less than 1% of adults. The posterior floor of the cavum vergae is constituted by the fornix commissure. This syndrome manifests as a separation of the leaflets of the septum pellucidum, extending posteriorly to the splenium of the corpus callosum. The anterior columns of the fornix delineate the anterior cavum septum pellucidum from the posterior cavum vergae. Historically, the midline cavities (cavum septum pellucidum and cavum vergae) were regarded as the fifth and sixth ventricles, respectively [12,13]; however, this notion is undermined by their lack of choroid plexus. The cavum vergae is delineated anteriorly by the posterior margin of the cavum septi pellucidum, inferiorly by the body of the fornix, and superiorly and posteriorly by the corpus callosum.

Midline cysts are seen in 0.04% on imagistic explorations (CT or MRI) [5] and are classified in two major groups: asymptomatic, that communicate with the ventricular system and are discovered incidentally on scans performed for other suspected intracranial pathology, often remain stable and do not require treatment; and symptomatic cysts, less frequent, always non-communicating (with the ventricular system or subarachnoid space), may be associated with other structural brain modifications [14,15] or it may signify the progression of a communicative cyst that has transitioned to a non-communicant state by mechanisms such as fluid secretion by the cyst, the presence of migrating ependymal cells leading to cyst growth, or the check valve phenomenon between the cyst and the subarachnoid space. Head injury was also proposed as mechanism in the cyst enlargement, but the exact mechanisms of cyst expansion remain undetermined [16].

As for the association of the midline cysts and type 1 neurofibromatosis, we found no reports in the English literature.

The symptomatology can be divided in two groups:

1st group in which the manifestations are secondary to elevated intracranial pressure, associated with cerebrospinal fluid circulation disorders at the foramen of Monro due to CSP, leading to obstructive hydrocephalus from intermittent obstruction, and include: headaches, nausea/vomiting, papilledema, and loss of consciousness [3,16].

2nd group in which the manifestations are secondary to direct compression on the structures surrounding the CSP.

Compression of the hypothalamo-septal triangle, situated within the area delineated by a line extending from the posterior aspect of the anterior commissure to the dorsal surface of the optic chiasma, then to the junction of the rostrum and genu of the corpus callosum, and returning to the anterior commissure. Certain symptoms observed in this condition, namely neuropsychiatric, autonomic, and visual are due to the compression of this area. Symptoms may encompass emotional lability, erratic conduct, alterations in mental status, deterioration in academic performance, sleep disturbances, enuresis, incontinence, anorexia, atypical epigastric sensations, disruptions in sleep patterns, hypothermia, and weight loss [3,16].

Alteration of vascular structures accompanied by compromised deep venous drainage. Dandy was the first to identify the distortion in vascular structures, while Aoki observed the chronic impairment in deep venous drainage, specifically in the deep vein system and subependymal vein, which could lead to motor or sensory deficits [16,17,18,19].

The visual structures, specifically the optic chiasm and optic tract, may experience compression either directly from the cyst or indirectly due to hydrocephalus [16,20].

The patient may exhibit nystagmus, sixth cranial nerve palsy, reduced visual acuity, visual field defects, papilledema, optic pallor, and retinal hemorrhage [16].

3.2. Imaging

MRI scan is the preferred imagistic technique to sustain the diagnosis of symptomatic CSP and offers high resolution images in order to define the cyst content, and define the relationships with the key anatomic structures (thalamus, internal cerebral veins, fornices).

The preferred sequences for the diagnosis are:

• T1-Weighted Images: Midline cysts typically appear hypointense (dark) on T1-weighted images.
• T2-Weighted Images: These cysts usually appear hyperintense (bright) on T2-weighted images, reflecting their fluid content.
• Fluid-Attenuated Inversion Recovery (FLAIR) Images: The cysts often remain hypointense on FLAIR images but may vary depending on the protein content of the cyst.
• Diffusion-Weighted Imaging (DWI): Most cysts do not show restricted diffusion.
• Contrast Enhancement: Midline cysts generally do not enhance with gadolinium.

The MRI can also help in identifying the structural modifications on the adjacent anatomic structures but also in defining the cyst type (communicating/non-communicating) by using the cine MRI sequences.

CT Scan may be useful for initial assessment, especially in emergency settings, helps identify calcifications and acute hemorrhage.

3.3. Differential Diagnosis of Midline Cysts

Cavum Septum Pellucidum (CSP)—Slit-like or triangular fluid-filled space located between the leaflets of the septum pellucidum. Imaging Characteristics: It generally exhibits hypointensity on T1-weighted MRI and hyperintensity on T2-weighted MRI. It does not exhibit enhancement with contrast and is typically situated anterior to the foramen of Monro.

Cavum Vergae (CV)—extension of the cavum septum pellucidum that extends posteriorly beyond the foramen of Monro towards the splenium of the corpus callosum. Imaging Features: Similar to CSP.

Cavum veli interpositi (CVI)—This condition represents an anatomic variant characterized by a dilatation of the normal cistern of the velum interpositum, exceeding 1 cm in size. It is situated inferior to the splenium of the corpus callosum and the column of the fornix, and superior to the internal cerebral veins. The structure is triangular, with the apex oriented anteriorly, extending to the foramen of Monro. Imaging Characteristics: Analogous to CSP.

Arachnoid Cysts—Cerebrospinal fluid-filled sacs situated between the brain and the arachnoid membrane, typically observed in the middle cranial fossa, though they may also be present in the septum pellucidum region. Imaging Characteristics: Their signal intensity on all MRI sequences resembles that of cerebrospinal fluid and does not demonstrate enhancement with contrast administration. Mass effect may occur depending on the size.Pineal cysts are classified as arachnoid cysts located in the quadrigeminal cistern. The internal cerebral veins serve as a significant landmark, as their location may yield valuable insights into the cyst’s origin. The pineal gland is typically situated inferior to the internal cerebral veins, while the venous confluence of the internal veins encircles these veins at its lateral and inferior margins [11].

Colloid Cyst—benign cysts usually located in the anterior third ventricle near the foramen of Monro. They can cause obstructive hydrocephalus. Imaging Features: Typically hyperintense on T1-weighted images and variable on T2-weighted images. They may show restricted diffusion on DWI and occasionally enhance with contrast.

Neurocysticercosis—infection caused by the pork tapeworm Taenia solium, which can form cysts in the brain. Imaging Features: Cysts may vary in appearance depending on the stage of the disease. Viable cysts are often thin-walled with a scolex visible inside, and they may show ring enhancement with contrast during the degenerative phase.

Ependymal Cyst—cysts are lined by ependymal cells and typically found within the ventricular system or brain parenchyma. Imaging Features: They appear similar to CSF on MRI and do not enhance with contrast. They are usually asymptomatic.

Cystic Tumors—Cystic components of tumors such as gliomas, craniopharyngiomas, or pineal region tumors. Imaging Features: These cysts often have complex features, including solid components, irregular borders, and contrast enhancement. Associated peritumoral edema and mass effect are common.

Other pathologies that should be taken in consideration are: enlarged 3rd ventricle, vein of Galen aneurysm.

3.4. Treatment

The management of symptomatic cysts remains a subject of debate, lacking established standards or guidelines to assist clinicians in determining the appropriate treatment:

For small cysts spontaneous resolution is cited in the literature, through different mechanisms: spontaneous fenestration [1,21] secondary to conditions associated with increased intracystic pressure that create shear forces able to cause spontaneous fenestration: straining, coughing, crying, head trauma; the cyst content is reabsorbed by the capillaries and veins of the septal wall, with osmosis facilitating the displacement of fluid from the cyst into the ventricle due to a pressure gradient [5,22].

For large cysts causing hydrocephalus or neural compression, surgery represents the first choice, the primary goal of treatment being to relieve the mass effect caused by the cyst [3].

The first report regarding the surgical treatment of CSP being published by Dandy in 1931, who performed a transcallosal fenestration [18]. In 1995 was reported the first endoscopic fenestration of a midline cyst by Jackowski. Since then, ventricular endoscopy, through frontal or seldom posterior (occipital) approach has become the modality of choice to treatment of CSP cyst [23] with sufficient data in the literature to support the effectiveness and safety of the technique, in terms of infection, brain damage or damage to deep cerebral vein injury [4,24,25]. Other options, formerly used, include open craniotomy, stereotactic drainage [4,5,15] and shunting (cystoventriculoatrial or cystoperitoneal) [1].

Endoscopic access to the cavum via small frontal horns poses potential risks. The entry of the endoscope may result in tissue damage to adjacent parenchyma and bleeding, occurring within a confined and occasionally distorted cavity. We advocate the use of neuronavigation (optical or electromagnetic) during the endoscopic ventriculo-cystostomy, to assist and enhance the orientation and precision during the procedure [19]. The endoscope itself should be calibrated within navigation protocol in order to serve as a navigated tool to be able to provide continuous position if the instruments.

The endoscopic surgical technique involves the fenestration of the cyst within the ventricular system. Two approaches have been described by Miki: type 1, which extends from the anterior horn of the right lateral ventricle to the cyst and subsequently to the left lateral ventricle; and type 2, which proceeds from the cyst cavity to the lateral ventricles in a “inside out” manner [26]. In most series the frontal approach is the preferred and safest route [19].

In our case we performed a right frontal approach and did the fenestration of the cyst in the right lateral ventricle (fenestration of a single wall).

The ideal approach is to open both walls of the cyst but cases with unilateral fenestration are reported with good results [15,25,27]. Technically the perforation of the first wall is easily performed and does not pose any particular problems. The communication is made by concentric coagulation and sectioning of the remaining adherences (same technique used for the perforation of the septum pellucidum) [28] or more simply by advancing the endoscopic perforator against the cystic wall and by enlarging the stoma using a Fogarthy balloon, as described in the surgical technique. Care must be taken in order to ensure a sufficient large communication, particularly if unilateral fenestration is wanted.

In our case the patient showed no clinical improvement on follow up and the image remained stable, same dimension of the cyst, with no signs of flow through the stoma.

Given the condition, we assumed an early closure of the stoma and in order to verify the patency of stoma we performed a ventriculocystenography (Figure 3C,D), which showed that the contrast medium does not pass from the ventricular system in to the cyst.

The ventriculocystenography shows not only the absence of the contrast into the cyst cavity (despite a patent communication with the ventricular system found intraoperatively), but also a perturbation of CSF dynamics with a slow circulation of the CSF—delayed opacification of the ventricular system (at 35 min—after injection) and a different distribution of the contrast medium in the ventricular system (lower intensity in the frontal horns compared with the occipital horns) confirming a dysfunction in the CSF circulation within the ventricular system—which is probably at the origin of the clinical symptomatology.

There are previously CT cysternography studies performed by Miki et al. [26] in order to study the dynamics of CSF in patients with septum pellucid cyst, but there are done preoperatively, in order to identify a communication between the cyst and ventricular system. Our case is the first in the literature in which a CT cysternography was performed after fenestration and is showing the absence of the flow through the stoma despite an endoscopic confirmed patency.

During the second surgery we were able to identify the ancient stoma (Figure 5B), which surprisingly was patent, we continued the surgery with the enlargement of the first stoma and the fenestration of the contralateral cyst wall in the left lateral ventricle (Figure 5C). In performing a bilateral fenestration care must be taken in order to avoid injury of the fornix and septal vein within the ipsilateral ventricle and fornix, septal vein, thalamostriate vein, thalamus, internal capsule, on the contralateral ventricle.

The reasons for contrast enhancement not passing trough the stoma are not fully understood, most probably due to a impairment of CSF circulation with gradient pressure difference between the cystic and ventricular compartment. This theory is supported by the difference of contrast medium distribution within the ventricular system (given the patency of the foramen Monro) and by the fact that after bilateral perforation we obtained a reduction of the cyst size and improvement of the symptomatology.

It would have been of real help to have a PC-MRI (phase contrast magnetic resonance imaging) in order to investigate the CSF flow and obtain information about the velocity of flow in the ventricles, as this exploration, according to recent studies, has a measuring error of less than 10% [29].

4. Conclusions

Symptomatic cysts of the CSP, CV, and CVI represent a rare condition in adults that can be effectively resolved through surgical intervention. Neuroendoscopic surgery is a highly effective treatment and is considered the preferred approach for this condition, particularly in cases involving bilateral cyst walls, which provide the greatest likelihood of success regarding cyst reduction and symptom improvement.