Hydrocephalus is a term of Greek origin2 which describes an abnormal accumulation of cerebrospinal fluid ( CSF ) in the ventricles of the brain leading to an increase in the intracranial pressure.

Classification
Hydrocephalus is classified under 2 main subdivision : Communicating hydrocephalus and Non-communicating Hydrocephalus.

External or Communicating hydrocephalus occurs when communication exists between the fourth ventricle and the subarachnoid space 1 and an increase in the ventricular volume and the subarachnoid spaces of the cranium and spine is present. 2 Here the ventricular pathways are clear and a failure of reabsorption results in increased CSF . 3

Internal or Non-communicating Hydrocephalus occurs when there is a blockage at one of the ventricular levels and causes an excess of cerebrospinal fluid ( CSF ) 3 to be present within the ventricular system up to the level of the outlet foramina of the fourth ventricle.2 The common sites of obstruction are at the outlet foramina of the fourth ventricle, the aqueduct of Sylvius or at the foramina of Monro . 2

Aetiology
There are numerous causes for hydrocephalus. Prenatally determined hydrocephalus occurs due to congenital ( chromosomal ) malformations, maternal diabetes resulting in holoprosencephaly, neural tube defects, occipital meningocele and encephalocele. Dandy-Walker syndrome1 which occurs when the fourth ventricle distends into a huge cyst, 4 arachnoid cysts causes hydrocephalus.

Communicating Hydrocephalus occurs when there is an excess production of CSF in Choroid plexues papilloma, or in impaired CSF absorption which occurs in meningitis , Cerebral atrophy. 5

Noncommunicating Hydrocephalus occurs due to an obstruction to the flow of CSF in intracerebral tumors, Aqueduct or foramen stenosis , by blood in subarachnoid heamorrhage. 5

Congenital Hydrocephalus occurs due to Arnold-Chiari malformation in spina bifida cystica , also due to forking or stenosis of the aqueduct of Sylvius1. Atresia of foramina of Magendie and Luschka when the fourth ventricle distends into a large cyst ( Dandy-Walker syndrome) occurs as an autosomal recessive form and will result in hydrocephalus1. Developmental failure of subarachnoid cisterns and congenital toxoplasmosis is also another cause1.

Acquired Hydrocephalus Pyogenic or Tuberculous meningitis , intracranial tumors, intracranial tumors at birth, metastatic tumor and brain abscess 1.

Incidence
The incidence of hydrocephalus per 10 000 births around the world is particularly high in alexandria ( 20.8 ) , Belfast ( 12.5 ) and Dublin ( 35.0 ). A collaborative perinatal survey (Chung & Myrianthopolous 1975) found an incidence of 15 per 10 000 births , only half of which were evident at birth. 2 Infantile hydrocephalus where the common presenting sign is head enlargement during infancy occurs in 1 in 2000 live births. 4

In a study conducted by the World Health organization in Philippines it has been reported that Hydrocephalus ( Congenital type ) is one among the 12 most common birth defects occurring in that region. 6 In India hydrocephalus accounted for 9.5 out of 10, 000 infants with common craniofacial malformations. 6 A research done in the Royal Victoria Hospital in Gambia from January 1996 to May 1998 claims that children of ages in the range of 0.1 to 10 years accounted for 0.9% of the admissions to the hospital where Hydrocephalus was the top ranked in neurosurgical diagnosis . 7

Clinical Features
Infantile hydrocephalus occurs during infancy. The appearance and the size of the head are related more to the age of the onset of the hydrocephalus then to its cause. 1 The symptoms of infantile progressive hydrocephalus are vague and consists mainly of vomiting and irritability , but as vomiting is a non specific symptom and irritability is accounted for as a behavioral change, about 50% of the cases are considered asymptomatic . 2 The most common clinical sign is an inappropriately increasing head circumference ( until a child is eighteen months of age, the circumference of the head is approximately equal to that of the thorax an this ratio is disturbed in hydrocephalus 8, which assumes a globular shape with an overhanging forehead and a disproportionately small face. 1 The anterior fontanel which is normally measures 3 cm approximately and 2 cm transversely at birth and continues to decrease progressively in size with age, becomes enlarged, tense 8 and non-pulsative 1 , then clinical and radiological separation of the sutures ( which may gape widely1) and the scalp veins become distended ( which is an valuable sign in early cases of hydrocephalus 8with taut skin over the scalp . 2

When the obstruction to the cerebrospinal fluid pathway occurs later when the disease progresses, there maybe little or no enlargement of the head. 1 The classic presentation is of the signs of raised intracranial pressure as headaches, cerebral vomiting, a cracked-pot sound on percussion of the skull, papilloedema, radiographic changes in the bones of the skull. 1

The ‘sunsetting’ is another common sign in hydrocephalus. It occurs due to the compensation for the raised ventricular pressure.2 Here the eyeballs tend to be pushed downwards so that a rim of the sclera is visible between the iris and the upper eyelid1 and thus the patient is unable to look upwards 2 and appears to be always looking at the floor. 8 It is due to pressure on the superior quadrigeminal plate against the free edge of the tentorium causing paralysis of the fourth nerve. 2

Fig . Sunset eyes

Neurogenic stridor also occurs due to deranged lower brainstem function caused by bilateral corticobulbar disruption. There will be abnormalities in sucking and feeding in hydrocephalic infants with seriously raised intracranial pressure. 2 Other neurological manifestations are found such as squints, optic atrophy and specific paraplegia or tetraplegia. 1

Diagnosis
Various imaging techniques such as X-ray examinations, Computer Axial Tomography (CAT), Ultrasound and magnetic resonance imaging ( MRI ) are useful in the diagnosis purpose. X-ray examinations of the skull may show a ‘ Copper-beaten’ appearance, shallow orbits and splayed sutures . 2 CAT scans, MRI scans and ultrasounds are useful in detecting the abnormalities of the ventricles . 5 The scans will all define the ventricular size 2 and maybe useful in suggesting the site of block . 5

CAT scans provide information about the size and symmetry of the ventricles and also if there is any underlying cause for the disease. 2 However, a single scan has a limited use as it cannot be used if the hydrocephalus is progressive or arrested. 2 Periventricular lucencies, rounding of ventricles, absence of a cortical subarchnoid space and a spherical appearance of the third appearance instead of the usual barrel shape are seen on the CAT scans when there is increased intraventricular pressure from progressive hydrocephalus. 2

Repeated ultrasound investigations and MRI scans can be used to detect the progress of the condition. Also definitive CAT and MRI investigations are done prior to any surgical intervention.

Fig : A hydrocephalic MRI and a normal MRI scan respectively.

During neuroimaging, certain anatomical changes are seen in normal pressure hydrocephalus, such as flattening of cortical sulci, widening of temporal horns, a dilated third ventricle, enlarged Sylvian fissures, focally dilated sulci and an increased flow void signal in the aqueduct. 9 None of these signs have proved reliable as diagnostic markers – their presence merely supports the diagnosis. 9

Measurement of the circumference of the skull is also done to assess the progress of the disease. 3 Occipitofrontal circumference is a measurement of the circumference of the head around the occiput, or posterior aspect, of the skull, to the most anterior portion of the frontal bone. 3 The measurement should be taken with a device that cannot be stretched, such as a flexible metal tape measure. As everyone’s head is slightly different, the tape should be moved around the circumference of the head in order to obtain the ‘largest possible measurement’. 3

Ventricular CSF pressure monitoring is the only accurate way of assessing the activity of the hydrocephalus . 2 Until the anterior fontanel closes at 18 months , it is done by direct puncture of the ventricle via the fontanel. However, if repeated ventricular punctures should be required then a frontal ventricular access devise is inserted to the frontal horn of the right lateral ventricle to allow sequential pressure measurements . 2

Disturbed CSF dynamics induce metabolic and degenerative changes in the periventricular brain tissue. 9 It is well known that cerebral blood flow (CBF) is reduced globally, and regional reductions have been reported in frontal lobes and hippocampus, thalamus and basal ganglia and periventricularly. Oxygen metabolism is reduced in the basal ganglia and periventricular regions; in most cases above penumbra level with intact auto-regulation. 9CSF biomarkers have shown interesting changes in idiopathic normal pressure hydrocephalus.9 CSF TNF-α (a pro-inflammatory cytokine involved in apoptosis and toxic to oligodendrocytes) is very high before surgery and normal after surgery indicating that the altered CSF dynamics radically changed the inflammatory state. 9 Neurofilament protein an axonal marker has been reported as increased in several studies, indicating dysfunction or damage to the axons. 9 Sulfatide, a marker of demyelinisation, has been reported increased in patients with Binswanger’s disease but normal in NPH patients, potentially making it a good differentiating marker. The water content measured as apparent diffusion coefficient or fractional anisotropy is high in the periventricular tissue in acute hydrocephalus but normal in chronic or NPH patients. 9

Treatment.

Shunts and reservoirs
About 40 % of all the cases of hydrocephalus in infancy undergo spontaneous arrest, therefore surgical intervention is only confined to cases in which serial measurements of the skull circumference show progressive and rapid enlargement. 2 There are many surgical maneuvers devised for this disease, the most usual one where the CSF is drained by a one-way drainage system form the ventricles to another site. A shunt is a mechanical device designed to transport the excess CSF from or near the point of obstruction to a re-absorption site and it is implanted under the skin .10 There are numerous valves and shunt systems such as Spitz-Holter valve, Pudez-Hakim, the Denver . 2
A shunt system has two functions. It allows fluid to go only in one direction and the valve allows fluid to flow out only when the pressure in the head has exceeded some value (usually referred to as the “opening pressure”). This system regulates the amount of the CSF in the body so that not too much is taken, nor too little . 10
A shunt has 3 components. The first portion is the called the shunt catheter or proximal portion of the shunt. This is a small narrow tube (catheter), which is implanted into the ventricle of the brain, above where the obstruction has occurred. It is then connected to the valve and reservoir. 10 The valve controls how much fluid is withdrawn from the brain, it is then stored in the reservoir until it is released to drain down the distal (bottom) end. It is through the reservoir that the working condition of the shunt can be check and also samples of CSF can be obtained through it. The distal end is a small, narrow piece of tubing (catheter) which leads to the point where the excess CSF will drain and be absorbed by the body . 10
Shunts are composed of a silicone elastomer (plastic) and are often impregnated with barium. In general, there are fixed shunts or programmable shunts. A fixed shunt has fixed values for pressure adjustments while programmable shunts allows a greater range of choices in choosing the pressure at which the fluid drains.10 The pressure can be easily changed as the neurosurgeon has a magnetic device to change the setting, in the convenience of his office. 10 Newborns and infants often are implanted with a fixed shunt and when they are older the shunt can be replaced with valve and reservoir unit with a programmable shunt. 10
Various routes of drainage have been used. Among the popular drainage routes, the ventriculo-peritoneal drainage, the ventriculo-atrial drainage routes and the ventriculoazygous routes are the ones used.

The ventriculoatrial route was the earliest one to be used in which a tube was passed via the common facial vein to the right atrium 2 where the CSF was drained from the lateral ventricle into the superior vena cava and then into the atrium. 1 The most popular one is the ventriculo-peritoneal drainage 1 where the distal end of the shunt is placed in the peritoneum.

Patients may have active hydrocephalus (mean ICP above 12 mmHg), compensated hydrocephalus (mean ICP 5–12 mmHg) or even low-pressure hydrocephalus (< 5 mmHg). 9 In patients with active or compensated hydrocephalus, we recommend using low or very-low pressure opening ball-in-cone valves together with gravitational devices (GD). G-valves alone or adjustable valves plus GD are alternative options. 9

Fig – A ventriculo-peritoneal shunt.

Fig -A ventriculo-peritoneal and ventriculatrial shunts

Complications of CSF shunting
Shunt surgery, is the most common treatment for both pediatric and adult normal pressure hydrocephalus (NPH). However due to lack of clinical collaboration and because there is no robust evidence proving that any valve is superior, neurosurgeons face important dilemmas in choosing the most adequate shunt. 9 This step is essential for improving outcome and avoiding shunt-patient mismatch. The most frequent complications of shunt surgery are: over- and under drainage and infections. Over drainage presents as symptomatic subdural hygromas, haematomas and slit ventricles. Under drainage is either related to obstruction, disconnection, malpositioning, or migration of the shunt system or to a valve with, or set at, excessively high opening pressure, leading to functional under drainage. 9 Less frequent complications related to the surgical procedure are intracranial bleeding or pneumatocephalus, and in the case of adjustable valves, the likelihood for accidental readjustment. The type and rates of complications differ for pediatric and adult hydrocephalus. 9 During the first year after shunt surgery in pediatric hydrocephalus, 10–20% have a shunt infection and about 17% have shunt malfunction. In adult hydrocephalus, the complication rates for surgery are: infection 5–10%, mechanical malfunction 10–30%, and subdural haematoma, 10–15%.9

1. Shunt Blockage
Early complications occur when fontanels are still open, such as building fontanels, increasing head circumference, Poor feeding, Projectile vomiting, Impaired vision – sunset phenomenon, squint eyes. All are signs of the shunt not draining properly either due to a shunt blockage or malfunction.11 Survival analysis showed no significant relationship between the onset of the mechanical blockage and the type of the shunt, the age at reservoir insertion, the sex of the child, the etiology of hydrocephalus or the time relationship of the shunt insertion to reservoir insertion. 2 The complications are reduced by the introduction of a reservoir. It maybe due to the ability to measure the intracranial pressure directly and so reduce the number of unnecessary shunt revisions. 2

Complications follow later when the fontanels are closed such as headache, blindness, vision problems, developmental regression ( losing a skill that the child previously had), convulsions, vomiting and poor feeding leading to malnutrition. 11

2. Ventriculitis
Among the complications of cerebrospinal fluid shunting and intracranial pressure management by external ventricular drainage (EVD), infection is one of the most serious. 9 Shunt infections or Ventriculitis occur with fever, convulsions, signs of meningitis and redness along shunt track.11 Many factors influence the incidence of shunt infection, such as the length of the operation, the skin preparation and the type of shunt. 2 However shunt infections remain a problem in a significant number of children. 2 It is difficult to diagnose and there is still controversy about the optimal management. Several different treatment regimes have been suggested including vancomycin into the shunt and systemic therapy with oral trimethoprim and rafampicin. 2 The clinical consequences of ventriculitis include deterioration in cognition, which can result in decline in quality of life so that the patient becomes uneducable, unemployable and profoundly dependent. In ventriculoperitoneal shunts, infection often causes obstruction of the distal catheter and in some cases loss of absorptive capacity in the peritoneal cavity, requiring alternative routing of the shunt. In both shunting and EVD most infections are caused by staphylococci, but gram negative bacteria are also important, especially in EVD . 9

3. Slit Ventricle Syndrome
In patients with normotensive hydrocephalus the normal intracranial pressure in the sitting position is negative and approximately 5 mmHg. After a shunt insertion in the erect position, the pressures are approximately -18 mmHg.2 Therefore in most situations with the patient upright and mobile during the day, the pressures will be negative but when supine and in rapid eye movement sleep, there may be significant elevation of pressure. 2This has resulted in the concept of slit ventricles and the slit ventricular syndrome. 2

The slit ventricle syndrome incorporates three components : intermittent or chronic headache secondary to episodic ventricular catheter obstruction : a slit-like ( y shaped ) ventricles on the CT scan : and a slowed refill of the palpable valve mechanism. 2The pathogenesis of the slit ventricle syndrome involves a siphon effect of continuing CSF flow down a shunt tubing ( particularly with the ventriculoperitoneal route ), excessive drainage from thecoperitoneal shunts in patients who are predominantly in the upright posture and the possibility that with ventriculoatrial shunts the diastolic phase of blood flow may encourage CSF withdrawal from the distal end of the shunt. 2

The management of slit ventricle syndrome has involved several procedures such as the use of high pressure valves, an antisiphon device, a calve upgrade together with an antisiphon device, a sub temporal decompression, a volume-regulated shunt system and lastly the use of steroids and the head down position. 2

Shunts with adjustable valves enable the functioning pressure to be modified in situ and allow non-invasive management of complications such as over drainage and slit ventricles, and under drainage. 9 One problem with adjustable valves is that they can become re-set accidentally with magnetic fields, as in MRI, cell phones, headphones and home magnets. 9

Risk of infection can be reduced by shorter pre-operative hospital stay, less use of antibiotics with, where possible, shorter courses, locally targeted antibiotics (intraventricular route, antimicrobial catheters), and enhanced state spending on health care. Treatment of infection should include catheter removal, preferably with intraventricular antibiotics. Antimicrobial catheters have shown benefit in both shunting and EVD . 9

Alternative Treatment
Some patients can be treated with an alternative procedure called an Endoscopic Third Ventriculostomy (often referred to as an ETV, Third Ventriculostomy, or Third Vent). For this operation, a tiny burr hole is made in the skull and a neuroendoscope is utilized to enter the brain. A small hole (several millimeters) is made in the floor of the third ventricle. This allows the CSF to flow from the blocked ventricles into the open spaces surrounding the brain 10 via lamina terminalis . 2 If this procedure is successful, it will eliminate the need for a shunt. However, not everyone with hydrocephalus can qualify for this type of operation. It is also meant for patients older than 6 months of age.1
Choroid Plexestomy is also another operation done to treat hydrocephalus, but in most cases as hydrocephalus is due to an increased resistance to drainage rather than an over secretion of CSF and a reduction of over 50% of CSF production may not produce any substantial effect on the degree of hydrocephalus or pressure. 2

Various drugs have been shown to have an effect on the rate of production of CSF but it is unlikely that those drugs are a definitive management for progressive hydrocephalus. However various drugs can be used as additional measures to help control CSF pressure in various conditions as patients with external ventricular drainage due to ventriculitis. Drugs as Frusemide and Acetazolamide reduce CSF production by their ability to inhibit the action of Carbonic Anhydrase. 2 For any acute rise in intracranial pressure associated with hydrocephalus, Mannitol may reduce the pressure sufficiently to prevent coning. Other drugs with receptor sites on the choroid plexus may also reduce CSF production without diminishing the overall choroidal perfusion . 2

Conclusion
Universal guidelines in hydrocephalus have been absent through a lack of prospective and standardized trials to support recommendations for standards of care. As a consequence, prospective multicenter trials involving standardized reporting of diagnosis, treatment and outcome in a larger number of patients are evolving around the world.9 Therefore new experimental research programmes are conducted in experimental hydrocephalus and other aspects of the disease such as pharmaceutical modulation of the CNS ( CNS drug delivery), in order to underline and peruse the translational aspect of hydrocephalus research . 9