Slit Ventricle Syndrome - an overview (2023)

Slit Ventricle Syndrome

The importance of valve-regulated shunts, first used in the 1950s for patients with congenital hydrocephalus, cannot be overstated.⁹² However, the nonphysiologic regulation of CSF diversion has inadvertently led to chronic shunt-induced headaches in many of these patients. The effect of chronic, unremitting, CSF shunt–induced overdrainage in a growing child has been termedslit ventricle syndrome (SVS) and is associated with episodic headaches. SVS may be defined as the development of intermittent headaches, usually lasting 10 to 30 minutes, in a shunted patient with smaller than usual ventricles. In addition, the reservoir refill may be slow. Intermittent headaches, small ventricles, and a slowly filling reservoir have been termed theslit ventricle triad.⁹³

Children with chronic overdrainage may do well for many years as their ventricles collapse. The pediatric literature has estimated that small ventricles exist in as many as 60% of shunted children, only 10% of whom have symptoms.⁹³ Young adults, asymptomatic as children, may present with progressive headaches or proximal occlusions requiring surgery. In one estimate, ventricular enlargement may not be evident in at least 20% of patients.⁹⁴ Because this group of patients is at high risk for morbidity and even mortality, the diagnosis should be sought early and subjective complaints should not be disregarded despite stable imaging.

The general etiology of SVS is chronic, nonphysiologic CSF drainage. Although chronic low pressure and volume are likely involved, the intraventricular pulse amplitude hypothesized to maintain ventricular size may also be reduced by the pressure regulation of the shunt.^95,96 The etiology of the pain that is described may be low or high pressure. It is important to note that headaches may be associated with high pressures even as the ventricles remain small. The tendency of ventricles to remain small in SVS despite elevated pressures has been considered evidence of reduced compliance.⁷⁶ However, the ependymal or glial scarring purported to develop in the setting of chronic hydrocephalus that resisted ventricular expansion was not substantiated by pathology studies.⁹⁷ Vascular engorgement may be a mechanism of decreased brain compliance.⁹⁸ Increased vascular engorgement is seen intracranial hypotension^97,99,100 as caused by other origins of CSF leak. However, in the case of cerebral hypotension, the vascular engorgement is compensatory and associated with a sagging, and not a stiffer, brain. In IIH, the high venous pressures may reduce compliance. These patients with small ventricles and high pressures have similarities to those with SVS. However, the observation of the sudden conversion of slit ventricles into large ventricles with progressive increase in opening pressure or after reduction of subarachnoid volume and pressure via lumbar puncture (LP) (Fig. 199-2) suggests that a pressure differential and a higher than normal brain compliance could be the cause of the slit ventricles.

Abstract

Slit ventricle syndrome is a complication that occurs after years of overshunting in patients who had a ventricular shunt placed as an infant. The disease is characterized by severe, life-modifying headaches with normal or smaller-than-normal ventricles. Treatment can be difficult. Initially, it should include placement of an adjustable shunt valve with an antisiphon device. If severe symptoms persist, then accurate classification and treatment can be obtained through a ‘shunt-removal protocol.’ The primary goal of treatment is to control symptoms through normalization of cerebrospinal fluid dynamics followed by medical management.

Slit Ventricle Syndrome

In general, small ventricles in a child with a shunt are good, and large ventricles are bad. A small subset of 1% to 5% of patients with very small, or slit, ventricles becomes symptomatic with acute or chronic headaches, nausea, vomiting, and lethargy. These patients have been lumped together under the term slit ventricle syndrome (Fig. 32.15). This terminology is confusing as it has been used for multiple clinical entities.¹⁹ At one end of the spectrum is a child with small ventricles who is very sick as a result of intracranial hypertension. At the other end of the spectrum is an asymptomatic child with a harmless and inconsequential CT finding.

26 What is “slit ventricle syndrome”?

Slit ventricle syndrome occurs as a complication in 1% to 5% of patients after shunting procedures for hydrocephalus during infancy and was first described in the 1960s. These patients usually have had a shunt in place for years with overdrainage of cerebrospinal fluid resulting in very small ventricles. Slit ventricle syndrome is recognized as a triad of chronic, intermittent headaches accompanying findings of a slowly refilling shunt reservoir on physical examination and “slit” ventricles on radiographic evaluation. Additional radiographic findings include a “copper-beaten” appearance or “thumb printing” and scalloping of the inner calvarial table (Fig. 30-5). Excessive intracranial decompression may result in cranial vault collapse with secondary craniosynostosis. With continued brain growth within the now-restricted cranium, increased ICP recurs with potentially devastating consequences.

Slit Ventricle Syndrome

Slit ventricle syndrome is thought to occur from chronic overdrainage and results in noncompliant ventricles. The patient will present with cycles of shunt malfunction—when the ventricles are very small, they block the shunt. This is followed by ventricular expansion, unblocking the shunt and relieving the clinical symptoms. Several theories have been suggested as mechanisms behind noncompliant ventricles, including a link between venous congestion and increased brain elasticity, subependymal and periventricular gliosis leading to increased ventricular wall stiffness, or overshunting during the neonatal period leading to microcephaly. These patients can be difficult to manage because their ventricles do not significantly change on imaging even though the intraventricular pressure is high. In such cases, ICP monitoring is the “gold standard” for diagnosis. In cases where multiple shunt revisions have been performed, subtemporal window decompression has been shown to be effective in decreasing ICP.

Slit ventricle syndrome

Slit ventricle syndrome is a very challenging complication of shunt placement. Although the actual incidence is not known, slit ventricle syndrome has been reported to occur in 0.9% to 33.3% of shunted children and more commonly in older children than in infants.⁹ Radiographically, it appears as very small, slitlike ventricles. Clinically, it is associated with frequent headaches. The mechanism is controversial and probably related to multiple causes. Intermittent shunt malfunction, overdrainage of CSF, periventricular fibrosis, and decreased intracranial compliance all are suggested mechanisms. Thus it may be associated with increased or decreased ICP. Management is controversial and includes medical options such as furosemide, acetazolamide, and antimigraine medications, as well as surgical options such as revising the shunt, upgrading the pressure on the valve, changing the valve to a flow resistance valve, adding an antisiphon device, subtemporal decompression, and performing endoscopic third ventriculostomy.

Slit Ventricle Syndrome

A consequence of chronic overdrainage is slit ventricle syndrome. Nomenclature in the literature is confusing. Some authors define the condition as small ventricular size associated with symptoms of intermittent shunt blockage. When the ventricles are very small, the shunt blocks. As the ventricles expand, the shunt unblocks, thus creating a cycle of intermittent shunt blockage.⁸⁹ A product is noncompliant ventricles. There are three theories as to the pathogenesis of noncompliant ventricles; however, it is likely that the true pathophysiology involves more than one mechanism. The first is that ventricular pressure is intimately related to intracranial venous pressure and when CSF pressure drops, uncoupling occurs. This leads to increased venous congestion and increases brain elasticity. The second is that increased pressure with subependymal flow can cause subependymal gliosis and periventricular gliosis with increased ventricular wall stiffness. If this happens, intraventricular pressure would need to be higher than usual to obtain ventricular dilatation. The third proposed mechanism is that low-pressure valves in neonates lead to overshunting with radiologic slit ventricles, the development of microcephaly, and synostosis. This in turn predisposes the ventricular catheter to obstruction and prevents the ventricles expanding in response to obstruction.

This group of patients is among the most difficult to manage. They can be difficult to diagnose because their ventricles do not change significantly in size when the intraventricular pressure is high. The principles of management of a patient with slit ventricles and possible features of shunt blockage include accurate characterization of the intracranial pressure. Careful evaluation of the CT scan may demonstrate subtle changes suggestive of raised pressure, such as reduced CSF over the hemispheres. Intracranial pressure (ICP) monitoring, although invasive, is often required and is the gold standard investigation in the assessment for potential shunt malfunction in the context of complex hydrocephalus. Another recognized technique is to externalize the VP shunt and modulate the pressure according to symptoms. ICP monitoring, if performed, should be continued for 24 to 48 hours, in conjunction with a headache and activity diary, and should be maintained during sleep.

Treatment usually involves shunt revision. Variable pressure valves are often used in this instance so that the pressure can be altered with ease. CSF flow-limiting valves, such as the Orbis Sigma, may also normalize intracranial pressure, possibly by improving intracranial compliance. Intraoperative image guidance is important because the ventricular size is often so small. In cases where multiple shunt revisions have been performed, subtemporal decompression has been shown to be effective. By removing bone (in effect creating a new fontanelle), the defect can act as an alternative pressure relief valve to the shunt, thus increasing intracranial compliance. Endoscopic third ventriculostomy (ETV) and cranial vault expansions have also been attempted.

Shunt obstruction

Shunt obstruction is a common complication that can present with many nonspecific symptoms. Mechanical failures or obstructions can occur at any time within any of the three components. The most common proximal obstruction takes place when the choroid plexus or debris occludes the ventricular catheter tip.^41,42 In growing patients with a shunt placed at infancy, it is common to encounter a distal malfunction once the catheter tip dislodges from the peritoneal cavity. The surgical assessment is a combination of clinical findings interpreted on the backdrop of objective measures. Clinical findings consist of headache, CN VI palsies, upward gaze paresis, irritability, lethargy, nausea, and/or vomiting. Infants with a shunt malfunction may display irritability, poor feeding, increased OFC, and/or inappropriate sleepiness. It is important to inquire if the presenting signs and symptoms are the same as when the shunt malfunctioned in the past.

When a shunt malfunction is suspected, imaging studies consisting of a head CT as well as anteroposterior and lateral x-rays of the skull, chest, and abdomen should be performed (Fig. 40.7).⁴³ Proper imaging can detect changes in ventricular size, catheter disconnections, and fractures. Confirmation of the programmable valve setting with a skull x-ray film perpendicular to the valve is important in shunt-dependent patients and serves as a reference for symptoms with equivocal objective changes.

Noninvasive methods to demonstrate an obstruction include an evaluation of the scalp for a subcutaneous fluid collection. More invasive methods consist of a percutaneous puncture and aspiration of the valve reservoir by a 23-gauge or smaller needle. This can rapidly diagnose a proximal catheter obstruction based on the ease of fluid egress.⁴⁴ It can be a temporizing measure for intracranial hypertensive emergencies if immediate operative intervention is not feasible and allows the collection of CSF for analysis. A nuclear medicine shuntogram can be obtained by injecting radioactive tracer into the valve reservoir to determine the patency of the shunt system. Patients who are diagnosed with a shunt malfunction must be taken urgently to the operating room for a shunt revision.

In less urgent situations and indeterminate clinical data, a dilated fundoscopic examination may be of some use to monitor changes over time. The presence of papilledema is specific, but not sensitive, for detecting elevated ICPs. Age, duration of hydrocephalus, optic atrophy, and intrinsic properties of the brain all contribute to the variable presence of funduscopic clues of malignant ICP.^2,45

These symptoms are oftentimes confusing and may overlap with the slit ventricle syndrome in up to 22% of children with headaches and radiology characterized by collapsed ventricles.^46,47 Incontinence, worsening focal neurological deficits, seizures, and lethargy in patients with slit ventricle syndrome may represent a sudden increase in ICP. In adults, the most common reasons for shunt revisions relate to suboptimal drainage of CSF. With prolonged overdrainage, about 10% of patients may develop subdural hematomas, stenosis/ occlusion of the cerebral aqueduct, slit ventricle syndrome, intracranial hypotension, or premature closure of the skull sutures.^47,48

Complications that affect distal drainage locations range from inadequate placement to obstructions. In the setting of shunt-dependent hydrocephalus, abdominal discomfort preceding symptoms of inadequate CSF drainage and the presence of an abdominal mass are highly suggestive of a pseudocyst. An abdominal CT or ultrasound can confirm the presence of the fluid collection. Although the etiology for a delayed CSF malabsorption is unclear, an inflammatory reaction resulting in thickened peritoneum is observed.^49,50 Current theories suggest an infectious source, CSF protein moiety, or autoimmune allergic response. The cysts may be percutaneously aspirated, and the fluid cultured. If a potential infection is suspected, a shunt tap and/or period of externalized drainage may be necessary until an infection has effectively been ruled out.

Helpful Clues for Common Diagnoses

Shunt Malfunction

A common complication of CSF shunting is malfunction from underdrainage of CSF (see Fig. 6.18). Generally, this is due to an obstruction or disconnection causing impedance of CSF drainage anywhere along the course of the shunt system.⁶⁴ Patients present with symptoms of increased intracranial pressure, which differ depending on the age group. Often the presentation can be with symptoms similar to a previous malfunction, though patients can develop a different constellation of symptoms with subsequent obstructions, and such complaints should not be dismissed.

Shunt malfunctions can be proximal, from obstruction of the ventricular catheter, or distal, from a blockage in the extracranial components. Ventricular catheters that migrate toward the choroid plexus are more prone to occlusion. Disconnections can be seen along the distal tubing in areas with increased movement, generally occurring in children undergoing growth spurts in areas with increased movement. The presence of multiple tubing connectors puts the shunt at risk for disconnection (Fig. 6.19). With time distal tubing can calcify, predisposing the shunt system to fracture.

Shunt catheters can migrate and dislodge. Proximal catheters can malfunction from migration into the brain parenchyma or subependymal space, either because of initial misplacement or because of continued head growth in children or ventricular collapse. Sometimes catheters can even migrate outside the cranial vault. Ventricular catheters connected to reservoirs are felt to be less likely to migrate. Particularly in children undergoing growth spurts, catheters can dislodge from the peritoneum, especially if not enough tubing was initially placed in the abdomen.

If a shunt obstruction is suspected, the initial evaluation includes imaging studies. A CT of the head allows for evaluation of the ventricles, especially when compared to previous scans. Though many shunted patients present with some degree of ventricular enlargement if the shunt becomes obstructed, those with altered ventricular compliance (e.g., slit-ventricle syndrome) may not show any change in ventricular size on imaging studies with a malfunction.³⁰ A shunt series is also obtained, which includes radiographs of the skull and the body along the peripheral shunt tract, which allows for evaluation of the continuity of the distal tubing. Other adjunctive studies include radionuclide scans, which require injection of a tracer into the reservoir, which travels into the ventricle and then through the distal tubing.⁶⁵ Failure of visualization of the tracer into the peritoneum indicates a shunt failure.

The valve can be examined at the bedside. The valve can be compressed against the skull. If the valve depresses but does not refill, it may indicate a shunt system obstruction. The shunt reservoir can also be accessed percutaneously with a small-gauge needle (23-25 gauge butterfly needle). Good flow of CSF indicates that the proximal part of the shunt is patent; in addition, ICP can be measured. In patients with symptoms concerning for shunt malfunction, but with imaging studies that are equivocal, CSF pressure can be measured by performing a lumbar puncture and checking the opening pressure, if there are no contraindications (e.g., mass lesion, history of myelomeningocele).

CSF shunt malfunctions require prompt operative revision. Most shunt malfunctions are secondary to occlusion of the ventricular catheter. When possible, a new ventricular catheter can be inserted before removing the old obstructed catheter. If there is resistance to removing the obstructed catheter, a stylet can be inserted into the catheter and monopolar cautery can be used along the stylet to free it from tethering tissue (e.g., choroid plexus adhesions). Sometimes the new catheter can be inserted without a stylet along the trajectory of the malfunctioning catheter, but sometimes such a catheter may again become obstructed by scar tissue.

Shunt malfunction can also be observed from shunt overdrainage.⁶⁶ This is can be seen with a variety of shunt valves, and is particularly augmented by the negative hydrostatic pressures generated when a patient is upright. Common symptoms include low-pressure headaches more pronounced in the upright position. A review of the literature by Pudenz and Foltz revealed that complications of overdrainage occur in at least 10% to 12% of patients with shunted hydrocephalus, usually within 6.5 years from the time of initial shunt placement.⁶⁷ Overdrainage complication includes the formation of subdural hematomas, intracranial hypotension, craniosynostosis and microcephaly, and slit-ventricle syndrome.⁶⁷ Valve pressure upgrades and the addition of antisiphoning devices may help with overdrainage symptoms.

Occasionally patients with known shunted hydrocephalus can present with concerning symptoms in the setting of small ventricles on imaging studies. Slit-ventricle syndrome refers to headaches lasting 10 to 90 minutes in the setting of imaging studies showing small ventricles and slow refill of pumping devices.⁶⁸ However, consensus is still lacking as far as the exact definition of the condition, and evaluation and treatment paradigms. Overdrainage symptoms are treated accordingly, while patients with increased ICP without ventriculomegaly are treated with shunting procedures such as lumboperitoneal shunt placement.

Subdural hematoma (SDH), acute or chronic, may occur from brain collapse due to ventricular overshunting, with resultant tearing of bridging veins. SDH can be ipsilateral to the side of the shunt (more common), contralateral (less common), or bilateral. Symptomatic SDHs should be removed, and the shunt valve pressure may need to be upgraded or a siphoning control device may need to be added.