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Cerebrospinal Fluid and its Abnormalities

  1. Michael Chan,
  2. Sepideh Amin-Hanjani

Published Online: 15 JAN 2010

DOI: 10.1002/9780470015902.a0002191.pub2

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How to Cite

Chan, M. and Amin-Hanjani, S. 2010. Cerebrospinal Fluid and its Abnormalities. eLS. .

Author Information

  1. University of Illinois at Chicago, Chicago, USA

Publication History

  1. Published Online: 15 JAN 2010

Introduction

  1. Top of page
  2. Introduction
  3. Pathophysiology of the Disease
  4. Frequency and Clinical Importance
  5. Major Clinical Features and Complications
  6. Approaches to Management
  7. Summary
  8. References
  9. Further Reading

Cerebrospinal fluid (CSF) forms a crucial component of the central nervous system (CNS) environment. It is the fluid which bathes the brain and spinal cord. As a result its production, circulation and absorption affect the homeostasis of the CNS milieu.

CSF circulation

CSF is found within the four ventricles of the brain, and the subarachnoid space surrounding the brain and spinal cord (Figure 1). It is formed primarily within the ventricles and circulates from the lateral ventricles through the interventricular foramen of Monro into the third ventricle, then down the cerebral aqueduct of Sylvius to the fourth ventricle (Figure 1). Outflow channels from the fourth ventricle – the foramen of Magendie and paired foramina of Luschka – lead out into the subarachnoid space which forms fluid-filled cisterns at the base of the brain. The CSF flows upward from the basal cisterns over the convexity of the brain, and down into the spinal canal. Over the brain surface, the fluid can extend into the sulci and even into the depths of the cerebral cortex through Virchow–Robin spaces. CSF flow through the ventricles and subarachnoid space is assisted by arterial pulsations, which create a constant ebb and flow. There is a small net movement forward, reflecting the overall pressure gradient. See also Cerebral Cortex, and Vertebrate Central Nervous System

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Figure 1. Pathways of cerebrospinal fluid (CSF) circulation: CSF is formed in the ventricles, circulates to the subarachnoid space and is absorbed into the venous system by the arachnoid villi. Only approximately 25 mL of the 130 mL around the brain and spinal cord is contained within the ventricles; the rest is housed within the subarachnoid space.

CSF production and composition

CSF is secreted mainly by the choroid plexus (a network of capillaries surrounded by cuboidal or columnar epithelium), a fact that was demonstrated by Cushing who directly observed CSF forming on the surface of human choroid plexus (Cushing, 1926). However, as evidenced by the continued production of CSF even after removal of the plexuses, there are other sources of CSF. Extrachoroidal CSF production is believed to be the product of fluid movement from capillaries into the brain parenchyma, subsequently entering the ventricular system across the ependymal lining of the ventricle. The proportion of CSF arising from this source is unknown but is believed to be less than 50%.

The choroid plexus itself is a functionally three-layered membrane between blood and CSF consisting of the endothelial wall of the choroidal capillary, scattered pial cells and collagen and the choroid epithelium (derived from the same layer of cells that forms the ependymal lining of the ventricles). Strands of this vascular and highly convoluted membrane are found in all four ventricles, and appear macroscopically as reddish fronds of tissue. Although the capillaries of the choroid are freely permeable to solutes, the choroidal epithelial cells form a barrier; adjacent cells are connected by tight junctions that occlude the extracellular space around them, impeding the movement of peptides and other molecules. See also Blood–Brain Barrier

CSF is a clear, colourless liquid, low in cells and protein but otherwise generally similar to plasma in its ionic composition. However, it is not merely an ultrafiltrate of blood. The choroid plexus has both filtration and secretory properties; its epithelium, like other secretory epithelia, is specialized with many basal infoldings, numerous apical microvilli and abundant mitochondria indicating the capacity for energy-dependent secretory functions. Furthermore, the formation of CSF is affected by certain metabolic inhibitors, suggesting the presence of an energy-requiring process. Careful analysis of CSF contents reveals that its ionic composition does vary from plasma in ways that are not consistent with an ultrafiltrate (Table 1). CSF contains an excess of magnesium and chloride, and a deficiency of potassium, calcium and bicarbonate. These concentrations are maintained at very stable levels even in the setting of changes in plasma concentration. Filtration of blood occurs through the fenestrations of the choroidal capillaries, followed by the active transport of substances across the epithelium into the ventricle (Figure 2). Water then follows passively to maintain the osmotic balance. There are also specific transporters for certain nutrients, vitamins and other substances.

Table 1. Composition of CSF and plasma in humans
ConstituentMean CSF concentrationMean plasma concentration
  1. Source: Adapted from Fishman 1992.

Osmolarity295 mOsm L−1295 mOsm L−1
Sodium138.0 mEq L−1138.0 mEq L−1
Potassium2.8 mEq L−14.5 mEq L−1
Calcium2.1 mEq L−14.8 mEq L−1
Magnesium2.3 mEq L−11.7 mEq L−1
Chloride119.0 mEq L−1102.0 mEq L−1
Bicarbonate22.0 mEq L−124.0 mEq L−1
pH7.337.41
Glucose60.0 mg dL−190.0 mg dL−1
Lactate1.6 mEq L−11.0 mEq L−1
Creatinine1.2 mg dL−11.8 mg dL−1
Total lipid1.5 mg dL−1750.0 mg dL−1
Total protein35.0 mg dL−17000 mg dL−1
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Figure 2. Transport across the choroid epithelium: cerebrospinal fluid (CSF) formation involves both capillary filtration and active epithelial secretion within the choroid plexus. Both active and passive transport processes are demonstrated within the epithelial cells of the plexus, resulting in regulation of CSF composition. With permission from Spector and Johansen 1989.

Some substances are also known to be transported in the reverse direction. For example, antibiotics such as penicillins are actively cleared from the CSF by the choroid plexus. This bidirectional secretory function allows the active transport of metabolites from CSF into the blood.

The overall rate of CSF formation is 0.35 mL min−1, approximately 500 mL day−1, leading to turnover of the entire CSF volume 3–4 times a day. The rate of the formation is relatively constant regardless of systemic blood pressure or intraventricular pressure. There is sympathetic and parasympathetic input to choroidal blood vessels and epithelium which can modify rates of formation.

CSF absorption

CSF circulating within the subarachnoid spaces over the cerebral hemispheres is absorbed through arachnoid villi into blood-filled venous sinuses, which lie between the inner and outer leaves of the dura. The arachnoid villi are microscopically visible outpouchings of the arachnoid through the dura mater; multiple villi aggregate to form structures called pacchionian granulations. Fluid in the spinal subarachnoid space circulates slowly towards the head. Along the way much of the fluid is absorbed into the venous system through arachnoid villi found in the dural sleeves of spinal nerve roots.

The actual process by which CSF absorption occurs is not fully elucidated, but is thought to involve one or a combination of the following strategies: flow occurring across a membrane (driven by the hydraulic pressure gradient between the CSF and venous sinuses), flow through open channels created by a series of tubules within the arachnoid villi or transcellular vesicular transport by pinocytosis. Regardless of the exact strategy the villi function as one-way valves, allowing bulk flow, i.e. all constituents leave with the fluid, including microorganisms, red blood cells, proteins and small molecules.

CSF functions

The CSF performs several functions that are crucial in protecting the brain and maintaining a stable milieu within the CNS. The three major functions can be summarized as follows.

  1. Mechanical support of the brain and spinal cord, and regulation of ambient pressure are probably the primary functions of CSF. The protective cushion of CSF prevents CNS structures from impacting on the bony skull and spinal column during movement, thus protecting against potentially injurious blows. Furthermore, suspension of the brain within fluid imparts buoyancy, resulting in the reduction of its effective weight from approximately 1500–50 g.

  2. Maintenance of homeostasis in the extracellular environment of neurons is another major function of CSF. CSF is in free communication with the extracellular fluid bathing the neurons and glia and thus indirectly regulates its composition. Furthermore, CSF acts as a sink for potentially harmful metabolites that can then be selectively absorbed by the choroid plexus or nonselectively removed by flow through the arachnoid villi.

  3. CSF also serves as a potential route for chemical messengers such as neuroactive hormones to be widely distributed to remote sites in the nervous system.

CSF dynamics

The cranial vault and vertebral canal form a rigid structure with a fixed capacity. The volume of its three major components, the brain tissue, blood and CSF dictate the intracranial pressure (ICP). Increase in the volume of any component occurs at the expense of the other two, a concept known as the Monro–Kellie hypothesis. As the volume of an intracranial compartment increases, accommodative mechanisms initially limit ICP increases. These mechanisms can include displacement of CSF from the cranial cavity into the spinal canal. The rate of production of CSF is nearly constant within a normal range of ICP, but with elevated ICP the formation of CSF decreases, probably due to reduced cerebral perfusion pressure. A linear increase in reabsorption is also evident with increasing ICP. Ultimately, however, accommodative compliance fails, resulting in exponential rises in ICP, with subsequent neurologic dysfunction and death. See also Traumatic Central Nervous System Injury

The CSF itself can be the source of increased ICP if its flow or absorption are hindered. These abnormalities of CSF dynamics will be addressed later.

CSF in disease states

Pathophysiological states affecting the nervous system primarily can lead to secondary alterations in the CSF. Such changes are reflected in the composition of the CSF and can aid in the diagnosis of disorders, ranging from infection to carcinoma to multiple sclerosis. A sample can be obtained for analysis by lumbar puncture, which involves removal of CSF by a needle inserted into the lumbar subarachnoid space. CSF pressure, which normally varies from 100 to 180 mm water can also be measured. Pathological conditions often lead to changes in the number and type of cells in the fluid, the chemical composition or the protein composition. Bacterial meningitis, for example, frequently results in an increase in the number of white blood cells, accompanied by an elevation of protein levels, a decrease in glucose concentration and an elevation of the CSF pressure.

Pathophysiology of the Disease

  1. Top of page
  2. Introduction
  3. Pathophysiology of the Disease
  4. Frequency and Clinical Importance
  5. Major Clinical Features and Complications
  6. Approaches to Management
  7. Summary
  8. References
  9. Further Reading

Abnormalities of CSF fall into several categories but generally result in the syndrome of hydrocephalus. Hydrocephalus, literally ‘water brain’, can be broadly defined as a hydrodynamic disorder of the CSF leading to an excess of intracranial CSF. This accumulation is usually in the ventricular space leading to enlarged ventricles, but not exclusively so. Generally this excess of CSF within the confined space of the intracranial cavity causes increases in ICP, leading to high-pressure hydrocephalus. However, hydrocephalus with ventricular enlargement can also be seen in the setting of apparently normal ICP, referred to as normal pressure hydrocephalus (NPH; Hakim and Adams, 1965). These forms of hydrocephalus differ in symptomatology but represent a continuum of the effects resulting from conditions which alter CSF dynamics and distribution. The severity and onset of the pathophysiological condition and the adaptability of the brain probably determine the type of hydrocephalus encountered, although high pressure is the predominant variety.

Hydrocephalus must be distinguished from cerebral atrophy, also referred to as hydrocephalus ex vacuo. The latter is a condition in which the ventricles are enlarged with an excess accumulation of CSF, but secondary to the loss of cerebral substance rather a pathophysiological imbalance between CSF formation and absorption.

Theoretically, hydrocephalus can arise in three distinct ways:

  1. overproduction of CSF,

  2. obstruction to the flow of CSF and

  3. inadequate absorption secondary to impaired venous drainage.

In practicality, almost every case of hydrocephalus is associated with an obstruction to the flow of CSF at some level in the pathways of CSF circulation.

Historically the term obstructive (noncommunicating) hydrocephalus, as introduced by Dandy and Blackfan in 1914, has been used to distinguish an obstruction preventing outflow of CSF from the ventricles into the subarachnoid space, as compared to communicating hydrocephalus, indicating a more distal extraventricular problem (Dandy and Blackfan, 1914). This terminology is somewhat misleading in that processes within the subarachnoid space leading to hydrocephalus are also obstructive. However, the distinction remains clinically useful in distinguishing aetiologies and assigning treatment options as discussed later.

Spinal cord cavitation with accumulation of CSF is known as syringomyelia. The condition is divided into communicating or noncommunicating syringomyelia. Communicating syringomyelia is a cavity that communicates with the central canal of the spinal cord and is also known as a hydromyelia. Noncommunicating syringomyelia does not involve the central canal. Pathophysiology of syrinomyelia and syrinx formation is not well understood. Compression of the spinal cord may contribute to their formation. Syringomyelia may be idiopathic or associated with Chiari malformation, tethered spinal cord, scoliosis, spinal tumours or trauma (Albright et al., 2008).

Overproduction of CSF

This is a very rare cause of hydrocephalus, and is almost exclusively seen in the setting of choroid plexus tumours (papilloma or carcinoma). Even in such cases other factors such as direct compression and obstruction of the CSF pathways by the tumour may contribute to the hydrocephalus. Hypervitaminosis A is also believed to be associated with hydrocephalus via this mechanism. See also Brain Cancers

Obstruction to CSF flow

Obstruction to CSF flow is by far the most frequent aetiology for hydrocephalus. Various pathological processes underlie the blockage: congenital malformations leading to focal narrowing of the CSF pathways (aqueductal stenosis); mass lesions (tumours/haematomas) intrinsically or extrinsically compressing CSF pathways; inflammatory processes inducing leptomeningeal fibrosis and obliteration of arachnoid villi (infection and haemorrhage). See also Traumatic Central Nervous System Injury

Impaired cerebral venous drainage

Increases in venous sinus pressure have long been hypothesized as an aetiology of hydrocephalus based on a presumed impairment in CSF absorption. Although the typical picture of ventricular enlargement and high ICP has not been definitively linked to such a mechanism, venous hypertension has been proposed in the aetiology of pseudotumour cerebri (benign intracranial hypertension), a syndrome of increased ICP without associated ventriculomegaly. Pseudotumour cerebri is discussed in detail elsewhere. In infancy, elevated cerebral venous pressure can potentially lead to accumulation of CSF in the subarachnoid space rather than the ventricles, so-called external hydrocephalus. See also Benign Intracranial Hypertension

Frequency and Clinical Importance

  1. Top of page
  2. Introduction
  3. Pathophysiology of the Disease
  4. Frequency and Clinical Importance
  5. Major Clinical Features and Complications
  6. Approaches to Management
  7. Summary
  8. References
  9. Further Reading

Hydrocephalus has an approximate prevalence of 1–1.5% within the population. The frequency and aetiology of hydrocephalus varies with age. In the paediatric population a congenital abnormality is the most common aetiology and results in hydrocephalus in approximately 3–4/1000 live births.

Paediatric hydrocephalus

The aetiologies for hydrocephalus in a series of 170 paediatric patients are outlined in Table 2.

Table 2. Aetiology of hydrocephalus in 170 paediatric patients
AetiologyNumber
  1. Source: Adapted from Amacher and Wellington 1984.

Congenital113 (66.5%)
Perinatal haemorrhage18 (10.6%)
Tumour18 (10.6%)
Infection13 (7.6%)
Trauma/subarachnoid haemorrhage8 (4.7%)
Prenatal aetiologies

The prenatal conditions giving rise to congenital hydrocephalus include the general categories of developmental/genetic abnormalities and infectious agents.

Developmental abnormalities

Several malformations of brain development lead to neonatal hydrocephalus. Aqueductal stenosis, a sporadic developmental abnormality with stenosis of the aqueduct of Sylvius has an incidence of 0.5–1/1000, and accounts for approximately 10% of all neonatal hydrocephalus. The Dandy–Walker malformation, characterized by cystic expansion of the fourth ventricle with poor communication to the subarachnoid space, results in 2–4% of neonatal hydrocephalus. The Chiari type II malformation (Arnold–Chiari malformation) is associated with a constellation of CNS abnormalities, including hydrocephalus. Changes in the posterior fossa result in presumed compression of the outlets of the fourth ventricle with subsequent impairment of CSF outflow. Myelomeningocoele has also been associated with hydrocephalus with an incidence of 0.2/100 000 patients (Green et al., 2007).

Infection

In utero infections involving the CNS can induce hydrocephalus. Congenital toxoplasmosis is one such infection that causes secondary aqueductal stenosis in addition to parenchymal damage, as well as certain viral infections, such as cytomegalovirus which causes a basal arachnoiditis, thus impairing CSF flow. See also Cytomegalovirus Infections in Humans, and Toxoplasmosis

Genetic

Rare familial disorders have been implicated. X-linked hydrocephalus, also known as the Bickers–Adams syndrome, is a recessive disorder that results in hydrocephalus and mental retardation. Hydrocephalus may also be a feature of major aberrations affecting other chromosomes. See also Chromosomal Genetic Disease: Structural Aberrations

Postnatal aetiologies

The postnatal aetiologies for hydrocephalus in the paediatric population are most commonly related to tumours, although other causative conditions exist.

Mass lesions

An expanding mass, whether a tumour, abscess or arachnoid cyst, within the brain can cause obstruction of CSF flow. Tumours, like other mass lesions, can block CSF flow either by extrinsic compression of pathways, or intrinsic growth within the ventricular system. Yet another mechanism for tumours to obstruct CSF circulation is spread of tumour cells along the subarachnoid pathways, leading to blockage at this level.

Haemorrhage

Acutely, haemorrhage can form mechanical obstructions in the pathway within the ventricular system, cisterns, subarachnoid space and arachnoid villi. Inflammatory reaction to blood products may result in chronically induced fibrosis in the leptomeninges with subsequent persistent resistance to CSF flow, and permanent hydrocephalus. The causes of haemorrhage in the paediatric population include head injury and rupture of vascular malformations. In premature infants, intraventricular extension of haemorrhage within the periventricular germinal matrix is a well-recognized phenomenon.

Infection

Bacterial meningitis, as with haemorrhage, can induce an inflammatory meningeal reaction with subsequent fibrosis, leading to hydrocephalus. Gram-negative organisms are frequently implicated, in addition to other agents such as tuberculous meningitis and cysticercosis. See also Bacterial Meningitis

Adult hydrocephalus

The frequency of aetiologies leading to hydrocephalus differs for adults presenting with hydrocephalus. Subarachnoid haemorrhage, especially of aneurysmal origin, is the most common cause, with hydrocephalus following up to 20% of cases. Tumours causing obstruction of the ventricles or their outflow are another important cause of hydrocephalus. In addition to intraventricular tumours, tumours may also obstruct the ventricular system extrinsically. Aqueductal stenosis, although a congenital condition, may present in adulthood. NPH may arise from the same aetiologies as high-pressure hydrocephalus, but typically if there is only low-grade scarring or obstruction of the ventricular system and subarachnoid pathways. NPH is limited to adults in the >60 year range. A significant number of cases appear to be idiopathic, especially in older patients, but are reminiscent of communicating hydrocephalus from other causes.

Major Clinical Features and Complications

  1. Top of page
  2. Introduction
  3. Pathophysiology of the Disease
  4. Frequency and Clinical Importance
  5. Major Clinical Features and Complications
  6. Approaches to Management
  7. Summary
  8. References
  9. Further Reading

The clinical presentation of hydrocephalus varies significantly based on the age of onset of the disorder. Acute or active hydrocephalus with increased ICP early in life manifests overtly with head enlargement. Later in life when the cranium is fused, other manifestations are apparent.

Infantile hydrocephalus

Before fusion of the cranial sutures by the end of the second year of life, increased intracranial pressure secondary to hydrocephalus results in enlargement of the cranium beyond normal growth curves. Increased head circumference is accompanied by other manifestations such as a bulging fontanelle, splaying of the cranial sutures and engorged scalp veins (reflecting the secondary increase in venous sinus pressure due to increased ICP). The infant will often be irritable with frequent episodes of vomiting. Poor head control and motor skills are frequently evident. Failure of upgaze from pressure on dorsal midbrain brainstem structures with relative down turning of the eyes, and retraction of the upper lids, leads to a ‘setting sun’ appearance to the eyes. As the condition progresses the child becomes more listless and unable to sustain activity. Ultimately, respiratory centres may be affected, resulting in irregular respirations and apnoeic spells.

Paediatric and adult hydrocephalus

Once the cranium has fused into a rigid structure, hydrocephalus is no longer overtly apparent as with the macrocrania seen in infancy. Clinical manifestations, however, again reflect increased ICP, but can range considerably in severity based on the rapidity of onset of the disorder. Headache is the most frequent complaint, usually bifrontal in location but may be generalized. Headaches may be worst in the mornings, temporarily relieved by vomiting, and exacerbated by lying flat or coughing. Nausea and vomiting commonly occur in association with the headache, and are also often worse in the morning. Examination of the optic fundi reveals papilloedema. See also Headache

Abnormalities in ocular movements include upgaze palsy (due to pressure on the dorsal midbrain), and double vision (due to pressure on the abducens nerve along its long course from the brainstem to the eye). There may be gait abnormalities, typically an unsteady, broad-based gait. Changes in mental status can be seen, ranging from impairment of recent memory to confusion. Intellectual function may be impaired with slowness of response, inattentiveness, distractibility, perseveration and inability to plan or sustain complex actions. Symptoms may arise slowly and subtly, but the rapid onset of high-pressure hydrocephalus can also be life-threatening, causing obtundation, coma and death.

NPH, the syndrome characterized by enlargement of the ventricles but normal CSF pressure, presents with a classic triad of clinical symptoms: gait disturbance, dementia and urinary incontinence. Symptoms of high-pressure hydrocephalus such as headache, nausea and vomiting, and visual changes are not seen. Papilloedema is absent and extraocular movements and upward gaze are intact.

Syringomyelia

Presentation of syringomyelia varies depending on the location of the syrinx. Patients may complain of dissociated sensory loss (normal light touch, position and vibration sense but aberrant pain and temperature perception), central cord syndrome (motor impairment in the upper more than lower extremities associated with variable sensory abnormalities), brainstem function disturbance (difficulty with cough or swallowing functions), scoliosis and pain (Albright et al., 2008).

Diagnosis

Definitive diagnosis of hydrocephalus is made through the use of neuroimaging studies. In infants with open fontanelles, ultrasound can be used as an initial imaging device. Ultimately, however, computed tomographic (CT) scanning illustrates the ventricular dilatation in addition to identifying the potential existence and nature of an obstruction in the CSF pathway. Magnetic resonance imaging (MRI) can offer more structural detail and evaluate for pathology with greater sensitivity (Figure 3). MRI is also the imaging of choice for evaluation of syringomyelia. Ventriculocisternography may be used to identify the normal CSF pathways and may assist with the diagnosis of cerebral aqueductal stenosis (Jones and Kinge, 2008). In cases of suspected NPH, lumbar puncture is required to measure and establish the presence of normal CSF pressure. See also Computed Tomography, and Magnetic Resonance Imaging

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Figure 3. T1 weighted axial and sagittal magnetic resonance images of the brain in patients with ((b) and (d)) and without ((a) and (c)) hydrocephalus. The ventricles are markedly enlarged compared to normal. The cerebral aqueduct (arrow) is patent and there is no evidence of obstruction within the ventricular system. This is a case of communicating hydrocephalus.

Approaches to Management

  1. Top of page
  2. Introduction
  3. Pathophysiology of the Disease
  4. Frequency and Clinical Importance
  5. Major Clinical Features and Complications
  6. Approaches to Management
  7. Summary
  8. References
  9. Further Reading

The management of hydrocephalus predominantly requires surgical intervention aimed at establishing an outflow for the excess intracranial CSF.

Surgical interventions

The standard current treatment of hydrocephalic conditions is the placement of a shunt device which diverts CSF beyond the level of suspected obstruction, most commonly to other locations in the body such as the bloodstream or body cavities capable of absorbing the fluid. Historically, other procedures had been advocated, from head wrapping in infants to repeated ventricular taps. In the early part of the century, Dandy introduced the technique of choroid plexectomy involving extirpation of the plexus from the lateral ventricles. The procedure was based on the premise that the choroid plexus was the sole source of CSF. Ultimately, it became clear that the procedure failed to control the progression of hydrocephalus and was abandoned primarily in favour of modern shunt techniques and other surgical interventions.

Shunts

The majority of patients with hydrocephalus require shunt insertion, a device for CSF diversion which establishes a communication between the CSF space and a drainage cavity. The choice of the receptive cavity varies on the circumstances discussed later. A typical CSF diversion shunt system consists of several basic components: a proximal catheter, a valve system and distal tubing (Figure 4).

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Figure 4. Ventriculoperitoneal shunt.

Proximal catheter

Ventricular catheters are typically inserted into the frontal horn of the lateral ventricle via a frontal or parietoccipital burr hole. In cases of communicating hydrocephalus CSF drainage from the lumbar CSF space is an option and carries the advantage of avoiding ventricular puncture. However, lumbar shunts have a much greater tendency for obstruction, and are used infrequently.

Valve

The valve is interposed between proximal and distal shunt components, usually near the site of ventricular catheter insertion. This device regulates the pressure and prevents retrograde flow of shunted CSF. Several valve designs exist which vary based on their mechanism of outflow regulation but the majority of designs are fixed-pressure valves functioning at high, medium or low settings. Recently, variable-pressure valves have become available, offering the potential advantage of fine-tuning ICP in shunted patients without reoperation. Variable pressure valves may be unintentionally reset by magnetic fields such as that found in MRI machines, cellular telephones and home magnets (Jones and Kinge, 2008). The ideal opening pressure of the valve for hydrocephalic patients is controversial.

Distal tubing

Silastic tubing is attached to the proximal catheter and tunnelled subcutaneously to the distal site of entry. The choice of the receptive cavity varies on the circumstances. Options include the atrium of the heart, the peritoneal space, the pleural space, the ureter and the gallbladder. In children especially, the peritoneum is a desirable recipient as it can accommodate long lengths of shunt tubing, allowing for growth without the need for replacement. The introduction of shunt systems has markedly decreased mortality associated with hydrocephalus. However, there are a variety of shunt-related complications including catheter obstruction, infection and CSF overdrainage. Acute shunt obstruction is estimated to occur at a rate of approximately 2% a year. Infection rates range from 10% to 20% during the first year after implantation in pediatric patients and 5–10% in adult patients. Subdural fluid collection formation from overdrainage can be observed in 2% of patients with shunts (Jones and Kinge, 2008). Patients may require repeated operative interventions to replace or revise the shunt system.

Aetiological treatment

Treatment of the underlying aetiology, such as resection of a mass hindering CSF flow, or correcting a malformation is the most desirable therapeutic strategy. However, such treatment does not always re-establish normal CSF hydrodynamics. Secondary changes such as leptomeningeal fibrosis may have developed, invoking the need for further intervention.

Membrane fenestration

In particular cases of obstructive hydrocephalus secondary to obstructions in the posterior fossa, such as aqueductal stenosis, the blockage can be ‘bypassed’. This is achieved by creating an alternative route for CSF flow into the subarachnoid space, typically by fenestrating the floor of the third ventricle. This procedure is performed endoscopically by the insertion of a neuroendoscope into the ventricular system, and creation of a hole in the floor of the third ventricle, allowing communication with the underlying cisterns and subarachnoid space. Success rates have approached 90% for first time fenestration. Complications may include injury to structures in the third ventricle, bleeding, stroke, infection and delayed closure of the opening. Repeat fenestration carries a higher complication rate of 55% versus 10% for first time fenestration (Jones and Kinge, 2008).

Syringomyelia treatment

Surgical treatment of syringomyelia includes treatment of associated chiari malformations, release of associated tethered cord or shunting of the syrinx. The latter can be performed with local shunting with a small ‘T-shaped’ tube to divert CSF into the subarachnoid space or distal shunting with implantation of catheter devices similar to the ventriculoperitoneal shunt (Albright et al., 2008).

Medical interventions

Medical management is aimed primarily at decreasing the rate of CSF formation by the choroid plexus, or alternatively, by increasing reabsorption with drugs such as isosorbide (a hypertonic osmotic agent). Diuretic medications such as acetozolamide, an inhibitor of carbonic anhydrase which contributes to ion exchange mechanisms within the choroidal epithelium, results in a 50% decrease in CSF production. However, the effects are generally transient, and clinical benefits have been unimpressive to date. Such treatments are merely temporizing measures in cases of mild hydrocephalus before a more definitive treatment strategy is undertaken, and are not an effective long-term treatment modality.

Summary

  1. Top of page
  2. Introduction
  3. Pathophysiology of the Disease
  4. Frequency and Clinical Importance
  5. Major Clinical Features and Complications
  6. Approaches to Management
  7. Summary
  8. References
  9. Further Reading

CSF forms a crucial component of the CNS environment. It is produced within the cerebral ventricles by a combined process of ultrafiltration and secretion, circulates over the brain and spinal cord and is absorbed into the cerebral venous sinuses. Pathological states, primarily those leading to the obstruction of CSF pathways, result in hydrocephalus, a condition characterized by an excess of intracranial CSF. Such an accumulation of fluid within the rigid cranial vault often leads to increases in intracranial pressure with potentially life-threatening complications. Surgical interventions, such as shunting of the fluid to extracranial compartments, are employed to treat the condition successfully.

End Notes
  1. Based in part on the previous version of this Encyclopedia of Life Sciences (ELS) article, Cerebrospinal Fluid and its Abnormalities by Sepideh Amin-Hanjani and Paul H Chapman.

Glossary
Arachnoid villi

Microscopically visible outpouchings of the arachnoid through the dura mater, protruding into the lumen of venous sinuses.

Hydrocephalus

Accumulation of intracranial cerebrospinal fluid (CSF) resulting in ventricular enlargement, and, frequently, increased intracranial pressure; caused by alterations in the production, circulation or absorption of CSF within the brain.

Normal pressure hydrocephalus (NPH)

Syndrome of ventricular enlargement with normal intracranial pressure, characterized by a symptom complex of dementia, gait instability and incontinence.

Papilloedema

Swelling of the optic nerve head visible on fundoscopic examination reflecting increased intracranial pressure; results from increased pressure in the nerve sheath slowing the axoplasmic transport within the optic nerve.

Virchow–Robin spaces

Extensions of the subarachnoid space along blood vessels which penetrate the brain parenchyma.

References

  1. Top of page
  2. Introduction
  3. Pathophysiology of the Disease
  4. Frequency and Clinical Importance
  5. Major Clinical Features and Complications
  6. Approaches to Management
  7. Summary
  8. References
  9. Further Reading
  • Albright AL, Pollack IF and Adelson PD (2008) Principles and Practice of Pediatric Neurosurgery, 2nd edn. New York: Thieme.
  • Amacher AI and Wellington J (1984) Infantile hydrocephalus: long term results of surgical therapy. Childs Brain 11: 217229.
  • Cushing H (1926) Studies in Intracranial Physiology and Surgery. London: Oxford University Press.
  • Dandy WE and Blackfan KD (1914) Internal hydrocephalus: an experimental, clinical and pathological study. American Journal of Diseases of Children 8: 406.
  • Fishman RA (1992) Cerebrospinal Fluid in Diseases of the Nervous System, 2nd edn. Philadelphia: WB Saunders.
  • Green AL, Pereira EA, Kelly D, Richards PG and Pike MG (2007) The changing face of paediatric hydrocephalus: a decade's experience. Journal of Clinical Neuroscience 14(11): 10491054.
  • Hakim S and Adams RD (1965) The special clinical problem of symptomatic hydrocephalus with normal CSF pressure. Journal of Neurological Sciences 2: 307327.
  • Jones HC and Kinge PM (2008) Hydrocephalus 2008, 17–20th September, Hannover Germany: a conference report. Cerebrospinal Fluid Research 5: 19.
  • Spector R and Johansen CE (1989) The mammalian choroid plexus. Scientific American 261: 6874.

Further Reading

  1. Top of page
  2. Introduction
  3. Pathophysiology of the Disease
  4. Frequency and Clinical Importance
  5. Major Clinical Features and Complications
  6. Approaches to Management
  7. Summary
  8. References
  9. Further Reading