Introduction
The term hydrocephalus is of Greek origin which means “the abnormal accumulation of fluid within the head“.1 Hydrocephalus results from the expansion of ventricles secondary to a block in the normal pathway of cerebrospinal fluid (CSF).2 The normal intracranial pressure in humans represents a balance between the intracranial contents that is blood brain n CSF. Any increase in the production, obstruction of flow or absorption will result in ventricular dilation.2 In hydrocephalus there is an increased pressure in the ventricular system.It is usually secondary to obstruction of CSF flow in the ventricular system(non-communicating) or failure of CSF reabsorption (communicating).6 In normal subjects CSF is formed at a rate of 0.3-0.5ml/min.In hydrocephalus patients on external drainage the CSF production rate is similar .
The production rate is similar in newborn and older children. A number of factors influence the CSF formation rate .Increased secretion may occur with a choroid plexus papilloma. Frusemide and acetazolamide reduce CSF production .Hypothermia will also reduce the rate of production and although pressure, when high intraventricular pressures exist the production rate falls,due to decreased choroidal perfusion. Ventricular outflow rates appear to be pulsatile so that peaks and troughs of CSF evaluation occur from ventricles when measured objectively in children undergoing closed ventricular drainage.2
It is usual to measure CSF pressure by lumbar puncture,but this may accurately reflect pressure in the brain,for example if there is obstruction by spinal tumours or herniation of brain through the foramen magnum .The main causes include tumours, abscesses, hydrocephalus ,haemotomas and benign intracranial hypertension.

Effects of raised intracranial pressure
A rise in the intracranial pressure is usually associated with headache ,especially in the morning, nausea, vomiting and loss of vision and balance. There may be false localizing signs, for example sixth nerve palsies. The most reliable sign is the appearance of papilloedema but this is not always seen even when the pressure is high. Urgent action to reduce pressure is needed in patients with impending herniation of brain through foramen magnum.4
Raised intracranial pressure results in either ischemic or brain shift. The ischemia results from a reduced cerebral perfusion pressure(CPP) (mean arterial pressure minus intracranial pressure). At levels of CPP below 60mmHg in the older child there is a progressive reduction in brain perfusion .At 40-50mmHg profound ischemic results. In the newborn , cerebral perfusion pressures 30mmHg may be associated with a normal neurodevelopment outcome.1 The subarachnoid space and the aqueduct are obliterated after shunting ,presumably because they are used less, and the patient become totally shunt dependant.
Fourth ventricular entrapment , with ataxia ,vomiting , cranial nerve disturbances and headache, is a result of outlet obstruction. Treatment is shunting of ventricle itself. Fistulous communications and diverticulae of the ventricles are usually an accompaniment of severe ventricular dilation.This produces a complex CT scan appearance and intraventricular contrast studies are needed to distinguish these from primary arachnoid cysts.1

CSF production
CSF production occurs by two mechanisms:- One mechanism which depends on the choroidal capillary blood flow where an ultra filtrate of plasma produced hydrostatically through the lax choroidal capillary endothelium (blood-barrier).Also an active process involving secretion of sodium into and out of the apical choroidal villi. The raised osmotic pressure causes water to follow passively. The second mechanism is a direct neurogenic stimulation of choroidal villi which is independent of choroidal blood flow.1 CSF is produced by choroid plexus in the lateral ventricles,from where it flows through the foramen of Munro into the third ventricle and then the fourth venricle via aqueduct of Sylvius. It leaves the ventricular system through the small openings in the roof of the fourth ventricle, the foramen of Magdie and Luksha. From here the fluid flows in the subarachnoid space before being reabsorbed into the blood via arachnoid villae.2 Therefore hydrocephalus is an increase in the ventricular or subarachnoid space 1 which is clearly visible in a CT scan 1,2,3
A rise of pressure in CSF above 250mm is usually due to a serious neurological disease which is caused by space occupying lesion that is obstruction to the outflow of venous return.4
Causes of Hydrocephalus
Hydrocephalus may result from a variety of causes including :
Communicating hydrocephalus: Due to excess production of CSF in (choroid plexus papilloma) or impaired CSF absorption(in meningitis) or Cerebral dysgenesis or atrophy.4 In congenital malformation,tuberculous meningitis,Arnold-Chiari malformation,subaracnoid haemorrhage and post-hemorrhagic in preterm infant.6
Non-Communicating hydrocephalus: Due to obstruction of flow of CSF (intracerebral tumours, aqueduct or foramen stenosis,by blood in subarachnoid haemorrhage).4,5 In atresia of outflow foramina of fourth ventricle(Dandy-Walker Malformation and post-intracranial infection.6

Acquired causes of hydrocephalus include the reactions of the meninges to pyogenic or tuberculous meningitis , intracranial haemorrhages at birth, metastatic tumours and brain abscess. In non-communicating hydrocephalus a dye such as phenolsulphonphthalein, when injected into one of the greatly dilated ventricles, fails to reach the subarachnoid space.When communication exists between the fourth ventricle and the subarachnoid space the hydrocephalus is of communicating type .The distinction in relation to surgical treatment.5 Internal hydrocephalus, external hydrocephalus, and the syndrome of intracerebral cerebrospinal fluid entrapment : a challenge to current theories on the pathophysiology of communicating hydrocephalus is still debatable.11 Obstruction of the CSF circulation distal to the fourth ventricle is a rare cause of noncommunicating hydrocephalus.12

Obstruction of CSF

A choroid plexus tumour may not only induce excessive CSF production but may also block the outlet of the ventricles intracranial haemorrhage or meningitis may cause leptomeningeal adhesions and obsruction to the CSF flow as well as impairing absorption by blocking arachnoid granulations.A common site for the obstruction is the aqeduct of sylvius. Congenital atresia may result inadequate lumen or a total blind-ending channel with forking of the upper and lower components of aqueduct. Occasionally there is a filamentous or membranous obstruction which may be broken down either by an increase in the intraventricular pressure or by surgical bouginage from the fourth ventricle. This rarely results in an effective reduction of the hydrocephalus because inadequate development of the peripheral subarachnoid pathways, which has resulted from the noncommunicating hydrocephalus, means the dynamics are only changed from a no communicating to a communicating hydrocephalus. The aqueduct of Sylvius may also be occluded by organized blood clot after intracranial hemorrhage, inflammatory exudate following ventriculitis or from an aqueductitis resulting from mumps.
Obstruction to CSF flow at the outlet foramina of the fourth ventricle may be secondary to intracranial hemorrhage or infection or may be due to congenital failure of the foramania of Magendie and Luschka to open during development. Occlusion of the fourth ventricle results in a fourth ventricular cystic dilation with atrophy of the cerebellum (the Dandy-Walker cyst). Tumors or clots, cysts or acscesses within or adjacent to the ventricular system may result in hydrocephalus. Thalamic tumors may obstruct the foramen of Monro and third ventricle and pontine or brainstem gliomas may distort the aqueduct of Sylvius although frequently such pontine gliomas are invasive throughout the brainstem and do not usually cause a gross hydrocephalus.Cerebellar tumors will affect the CSF flow from the fourth ventricle.A choroid cyst of the third ventricle may give rise to intermittent high pressure and hydrocephalus by obstructing the foramen of Munro in a ‘ballcock’ fashion.During distention of the cyst or venous distention about it there is obstruction of CSF flow through the foramen of Munro.With a possible change of posture the obstruction may be rapidly released and the pressure declines.These children with cysts of the third ventricle frequently present with a ‘bobble-headed doll’ syndrome and progressive loss of interlect with a particular frontal horn dilation.1
Hydrocephalus is a common complication of aneurysmal subarachnoid hemorrhage. Numerous studies have dealt so far with the triggering cause of the chronic cerebrospinal fluid (CSF) absorptional and circulatory disorders.The rate of the incidence of chronic hydrocephalus suggests that disturbance of CSF circulation and/or absorption may be drainage, which avoided in the majority of cases by continuous external ventricular or lumbar CSF.9

Decreased absorption of CSF
Decreased absorption may result from obstruction of the arachnoid villi or either peripheral subarachnoid pathways.Absorption (unlike formation) of CSF is apressure dependant phenomenon and measures linearly with CSF pressure.There are three types of absorptive defect.Normally CSF absorption begins at a mean pressure of 5mmHg.In some patients the opening pressure for absorption is elevated but the subsequent slope is normal . In others the slope alone is decreased and in the third group the resistance to absorption is increased at the pressure is raised.1

Factors causing progression of hydrocephalus
Observations in experimenta hydrocephalus suggest that after CSF obstruction the ICP rises acutely. This is followed by a stage of per ventricular edema which expanded ventricles and subsequently by an increase in CSF absorption. Ventricular dilation and its eventual size depend on the external support of the brain. In infants up to 16 months of age the support of the brain is weak from the poorly myelinated soft parenchyma and there are unfused sutures.Clearly the level of pressure is important at first in the pathogenesis of ventricular dilation,together with the known increase in the outflow resistance and a higher ‘pressure volume index’(PVI) tan could be predicted from the volume of cranial and spinal axis.
In term n preterm infants we frequently see levels of intraventriclar pressure of 5mmHg (above normal for age) which are sufficient to interfere with the cerebral blood flow velocity and have the potential to cause ischemia.
A number of physiological buffers come into play in response to the hydrocephalus. There is collapse of cerebral veins , a shunting of CSF from the ventricular to the spinal CSF compartment, expansion of the skull and a increase in the CSF absorption from the raised pressure. There may also be increased CSF absorption about the spinal nerve roots and paranasal sinuses etc .Once these compensatory mechanisms have been exhausted then further progression of the hydrocephalus will occur.
The sequence of events is that at first the pressure will increase. The dilation of the ventricles in response to this high pressure is termed ’active or progressive hydrocephalus’. Finally the pressure returns to the normal levels with severely dilated ventricles ,a state of arrest (compensated or arrested hydrocephalus).Sometimes the active process may be followed by an intermittent pressure pattern with ventricular dilation until arrested is reached .This intermittent pattern may be reversible .However significant elevation of the pressure with increasing ventricular dimensions to the point where brain perfusion is compromised necessitates CSF diversion procedures before shunt-dependant or compensated arrest occurs.1

Infantile Hydrocephalus
Hydrocephalus maybe due to congenital causes such as Arnold-Chiari malformation in spina bifida cystica .3,5 There is an elongation of the medulla. Abnormal cerebella tonsils descend into the cervical canal associated spina bifida is common and Syringomyelia may develop.3 Stenosis or forking of aqueduct of Sylvius.3,5 This is either congenital or acquired following neonatal meningitis or haemorrhage.3 Atresia of the foramina of Magendie and Luschka ,failure of development of the basal subarachnoid cisterns ,and congenital toxoplasmosis.5 Rarely the disease is inherited as a recessive form due to atresia of the aqueduct .There is a also an autosomal recessive form due atresia of the foramina of Luschka and Magendie when the fourth ventricle distends into a huge cyst(Dandy-Walker syndrome).3,5 Head enlargement in infancy occurs in 1 in 2000 live births.3 New born baby’s head circumference is measured with a paper tape measure and it’s centile noted. This is a surrogate measure of brain size.6 A variety of congenital abnormalities may lead to hydrocephalus which may be present before birth (and hence produce difficulties at birth) or develop during childhood or adult life.
Progressive enlargement of the head is usually obvious with failure of closure of the frontanelles. Milestones of development are delayed and the end result may be mental retardation complicated by epilepsy and motor impairment. CT scan or MRI may show the abnormality and sometimes the cause, the early implantation of a shunt may arrest the physical and mental retardation that would otherwise occur.4
Most common clinical features of progressive infantile hydrocephalus;
Symptoms- headache or irritability, vomiting, anorexia, drowsiness or lethargic.
Signs- tense anterior fontanel, splayed sutures, scalp vein distension, sunsetting, neck retraction or rigidity, papillary changes, Neutrogena stridor, decerebration. 1
L1 disease is the most common genetic cause of congenital hydrocephalus.7 Mutations in the L1CAM gene are associated with an overlapping clinical spectrum of four X-linked neurological conditions, characterized by hydrocephalus, mental retardation, lower limb spasticity and adducted thumbs. Brain anomalies are frequently present in L1 disease. We describe these anomalies by reporting a case of a male newborn presenting with congenital hydrocephalus along with corpus callosum agenesis and enlargement of the massa intermedia. These findings, in association with the presence of clasped thumbs, raised the suspicion of L1 disease, which was confirmed by the detection of a mutation in the L1CAM gene. In cases of congenital hydrocephalus, recognition of the brain anomalies associated with L1 disease may contribute to pursuing the genetic analysis needed for the diagnosis and genetic counseling.7

Hydrocephalus in Adult life 3
Hydrocephalus can be an unsuspected symptomless finding or imaging ,or infantile hydrocephalus can become apparent in adult life .Combinations of headache , conginitve impairment, vomiting , papilloedema ,ataxia and bilateral pyramidal signs occur. Hydrocephalus may develop in cicumstances:
Posterior fossa brainstem tumours obstruct the aqueduct or fourth ventricle outflow.
Following subarachnoid haemorrhage, head injury or meningitis(particularly tuberclous)
A third ventricle colloid cyst causes lateral ventricle enlargement, headache and papillaoedema . These rare intraventricular tumours also sometimes produce intermittent hydrocephalus,recurrent prostrating headaches with episodes of lower limb weakness.
Choroid plexus papilloma (extremely rare) secretes CSF.3
Head circumference – occipital circumference is a measure of head and brain growth .The mean of 3 measurement is used. It is of particular importance in developmental delay or suspected hydrocephalus.6

Clinical features
In infants with hydrocephalus the head circumference is disproportionately large or its rate of growth is excessive, the sutures become separated and the veins get congested.The anterior frontanelle pressure ,with the infant relaxed , will feel increased on palpation and will subsequently bulge. If left untreated ,the eyes deviate downwards ( setting-sun sign).The infant subsequently develops signs and symptoms of raised intracranial pressure .hydrocephalus may be diagnosed on antenatal ultrasound scanning , when the infant is asymptomatic . In older children , clinical features are due to raised intracranial pressure. 6
The appearance and size of the head are related more to the age of onset of the hydrocephalus than to its cause. Thus, hydrocephalus can obstruct the course of labour. In most cases the hydrocephalus only appears after birth. In infancy it causes a progressive enlargement of the head which assumes a globular shape with overhanging forehead and disproportionately small face. The increasing enlargement should be assessd by regular measurements of the skull circumference. The fontanel’s are greatly enlarged and somewhat tense, and the sutures may gape widely. Dilated veins are often prominent over the scalp. The eyeballs tend to be pushed downwards so that a rim of sclera is visible between the iris and upper eyelid. Neurological manifestations include squints, optic atrophy, and spastic paraplegia or tetraplegia. The degree of mental retardation is variable and not closely related to the thickness of the cerebral cortex. In severe cases failure to thrive and marasmus are common.
When the obstruction to the cerebrospinal fluid pathway occurs later in childhood there may be little or no enlargement of the head, but there will be then be such signs of increased intracranial pressure as headache, cerebral vomiting, a cracked- pot sound on percussion of the skull, papilloedema and radiographic changes in the bones of the vault.5
The symptoms of infantile progressive hydrocephalus are vague and consist of irritability and vomiting but about half without symptoms. The most common clinical sign is an inappropriately increasing head circumference, followed by a tense nonpulsatile fontaniel, then clinical and radiological separation of the sutures, scalp vein distension with taut skin over the scalp. It is important to realize that the classic adult presentation of raised intracranial pressure is rare in children (headache, vomiting, papilledema).
Vomiting is a nonspecific symptom in childhood, as are behavioral changes (irritability).
The most common sign of hydrocephalus is really a sign of compensation for the raised ventricular pressure. “Sunsetting’- the inability to look upwards -may initially be intermittent and later continuous. It is due to pressure on the superior quadrigeminal plate against the free edge of the tentorium causing paralysis of the forth nerve.
Neurogenic stridor is a result of deranged lower brainstem function caused by bilateral corticobulbar disruption and is a feature of pseudo bulbar paresis. Abnormalities of sucking and feeding may also occur in hydrocephalic infants with seriously raised intracranial pressure. 1
Papilledema is rare but distended retinal veins are common.
The symptoms of chronic hydrocephalus are an isiduos deterioration in school performance,intermittent headaches over many months,behavioral and personality changes ,failure to thrive dizziness. These are distinct from the signs and the symptoms of arrested hydrocephalus of long standing which include features of ataxic and spastic cerebral palsy, precocious puberty , mental retardation and specific learning problems. The clinical features of hydrocephalus with raised intracranial pressure may be extremely variable and any infant with a rapidly increasing head circumference but is otherwise asymptomatic is likely to have hydrocephalus if there is additional development retardation.1
Clinical features of decompensate hydrocephalus
The possibility of a blockage of a shunted hydrocephalus is suggested by additional signs of raised pressure median survival time for a verticuloperitoneal shunt is 4.31years.
Unusual features of raised ventricular pressure include Neutrogena pulmonary edema, profuse swelling, ptosis, Neurogenic stridor, pseudobulbar paresis and skin rashes.1
Symptoms- vomiting, drowsiness or lethargy, headache, anorexia, valve malfunction, sleep disturbans, seizures.1
Signs- No clinical signs (approx 25 %),decreased conscious level,acute squint .neck retardation.distended retinal veins, sluggish palpable valve mechanisms.1
Differential Diagnosis
This is rarely difficult. The most important differentiation in infancy is from chronic subdural hecatomb , because the latter condition is eminently curable. Subdural taps should always be performed in doubtful cases. In the rare genetic disorder called macrocephaly there is generalized enlargement of the brain although the child is mentally diffective and may have optic atrophy. It can be differentiated from hydrocephalus by pneumoencephalography, but ultra sound and CT scanning are now the preferred techniques as they are non-invasive, free from risk and less disturbing for the patient.5
Management
Assesment of ventricular dilation is with cranial ultra sound/CT/MRI scan treatment required to release the raise in intra cranial pressure and minimize risk of neurological damage. The main stay is insertion of ventricular shunt, but endorscopic treatment is being developed. Shunt revision may be required if there is symptomatic malfunction from obstruction, infection (usually with coagulase negative staphylococcus) which is unresponsive to antibiotics or over drainage of fluid.6
Treatment

Ventricul-atrial or ventriculo-peritoneal shunting becomes necessary when progressive hydrocephalus causes symptoms. neurosurgical removal of tumours should be carried out where appropriate ,sometimes urgently.3 It is essential to realize that 40 percent of all cases of hydrocephalus in infancy undergo spontaneous arrest. Surgical treatment should be confined to cases in which serials measurements of head circumference show progressive and rapid enlargement. Hydrocephalus develops in about 80% of cases of meningomyelocele, especially when the site is dorsolumbar . Cervical myelomeningocele (CMMC) is a rare entity in neurosurgical practice, which presents different clinical characteristics compared with other more common lumbosacral variant.10 It can be diagnosed by ultrsonography or CT scanning in the early weeks of life and before head enlarges .It is probably not influenced by repair of the meningomyelocele. Operating is indicated in all but the mildest cases of this nature. Operation must always be preceded by detailed investigations to confirm the diagnosis beyond doubt and to demonstrate the type of hydrocephalus. Many surgical maneuvres have been deviced for this disease. The most popular or perhaps ventriculo-peritoneal drainage , or the use of Spitz-Holter or Pudence-Heyer valves to drain CSF from the lateral ventricle into the superior vena cava or atrium.Torkildsen’s operation drains CSF from the ventricle to the Cisternamagna.but it is suitable only for the small group of patient’s of pure aqueduct obstruction. In all operations involving plastic tubes or silicon valves there is a likelihood of later obstruction to the flow of fluid. There is also a risk of chronic bacterium from colonization of the valve or tube. It is notoriously difficult to assess the longterm results of operations for hydrocephalus. Undoubtedly they should be undertaken only by experienced surgeons working in large centres.5
Normal pressure hydrocephalus is a rare syndrome that describes enlarged cerebral ventricles without cortical atrophy, with dementia , urinary incontinence and gait aapraxia, as usually in elderly .CSF constituents and pressure are characteristically normal. Ventriculo-peritoneal shunting occasionally helps.3
Selected normal pressure hydrocephalus (NPH) patients cannot be treated by shunt operation because of the procedure’s high complication rate.8