Hydrocephalus is a condition in which there is accumulation of CSF in the cerebrum due to a disturbance of formation, flow or absorption of CSF. It is a pathological condition rather than a specific disease.

Hydrocephalus occurs as an isolated congenital disorder in approximately 0.9-1.5/1000 live births.

Hydrocephalus in association with spinal dysraphism varies from 1.3 to 2.9/1000.

Dandy introduced the widely used and generalized terms communicating (due to a blockage outside the ventricles) and non-communicating (due to a blockage within the ventricles) hydrocephalus. Both are, in essence, obstructive, although at different sites. It may be acute or chronic, depending on time course.

Arrested hydrocephalus is an  asymptomatic condition with non-progressive ventriculomegaly.

Compensated hydrocephalus is a symptomatic condition, with non progressive hydrocephalus.

Normal pressure hydrocephalus is a misnomer. It describes a condition in older adults of intermittently raised ICP.

Non obstructive hydrocephalus is a term used to describe enlarged CSF spaces due to loss of brain- external hydrocephalus.

PATHOPHYSIOLOGY:

CSF production and absorption are in dynamic equilibrium, with average production equaling average absorption under normal physiologic conditions. CSF volume is approximately 150cc in adults and is produced at a rate of 14-36 cc/hour.  50%-80% of the CSF is derived from Choroid plexus. The remaining CSF is from cerebral parenchyma from the capillary endothelium.

Choroidal CSF is formed as an ultrafiltrate from the capillaries in the center of each villus. The ultrafiltrate is then processed by the choroidal epithelium and secreted by diffusion into the ventricles.

CSF circulates from the lateral ventricles to the third ventricle through the foramen of Monro and then to the fourth ventricle through the aqueduct of Sylvius. CSF then passes through the foramina of the fourth ventricle into the subarchnoid spaces, where it circulates to the primary site of absorption, the arachnoid granulations of the sagittal and transverse sinuses. The emissary veins of the dura and the lymphatic drainage system of the skull are other sites of CSF absorption.

For a constant CSF volume to be maintained, an equal volume of CSF must be reabsorbed by the arachnoid granulations. If the absorption fails, ventricles enlarge at the expense of the brain parenchyma, initially the immediate adjacent white or grey matter rather than the cortex.

Continued enlargement disrupts the ventricular lining and then the underlying white matter. There is an increase in its water content due to transependymal flow of CSF from elevated intraventricular pressure and the edematous parenchyma i becomes spongy. Axonal and myelin destruction can occur with this increase in extracellular water content. Ventricular diverticula may develop. Interhemispheric fissure becomes elongated and thinned out.

Expansion of the skull in infants and thinning and atrophy of the brain are resultant compensatory mechanisms. In addition, there is contraction of the cerebral blood volume, and alteration cerebrovascular circulation. CSF circulation is also altered.

Changes in Cerebrovascular circulation: Earliest change is the increase in cerebral venous pressure secondary to compression of the unsupported cerebral veins. Cerebral arteries are narrowed in chronic cases. Cerebral circulation time is prolonged. The blood flow in the white matter, especially around the frontal and occipital horns (prefrontal, parietal and visual association areas), is selectively impaired and the same improves after shunt surgery.

Changes in CSF circulation: In non communicating hydrocephalus, the subarachnoid CSF tends to flow normally towards the cerebral convexities, as it is not dependant on choroid plexus pulsations. In communicating variety, the flow is reversed back into the ventricles.

Hydrocephalus almost always results from an obstruction (mechanical blockage or poor absorption) in the CSF pathways and only rarely from overproduction of CSF, as in choroid plexus papilloma and meningitis.  

Poor absorption may be due to defective archnoidal villi or rarely, to  raised  venous pressure as in sinus thrombosis.

CLINICAL FEATURES:

In acute cases, the patient is ill and drowsy, and irritable, with headache, vomiting.

Infants with chronic hydrocephalus, present with poor feeding, vomiting, reduced activity, and drowsiness. There may be endocrine abnormalities due to prolonged pituitary compression.

centile.

Chorioretinitis in a child with hydrocephalus indicates an in utero infection with cytomegalovirus or toxoplasmosios.

In chronic cases, adults, usually complain of gait disturbances, memory loss, slowness of thought and action, and urinary incontinence. Papilledema and 6th nerve paresis may be the only clinical findings

Hydrocephalus in children:

Congenital hydrocephalus:

Hydrocephalus is commonly a congenital disorder that can occur as an isolated finding or as part of a complex congenital malformation syndrome. Congenital or primary hydrocephalus, with an incidence of 1 in 1,000 births, is usually a sporadic condition, but families with X-linked and autosomal recessive patterns of inheritance have been reported. The X-linked form is more common and is estimated to occur in 1 in 30,000 male births. This condition accounts for an estimated 25 per cent of male hydrocephalus not associated with myelomeningocele. Hydrocephalus that follows an autosomal recessive pattern has been described much less frequently.

Aquedect stenosis is the most common cause of hydrocephalus in the new born and may present at a later age as well. The aquedect may be congenitally stenosed or forked, having multiple blind outpouchings without patency. In addition, aquedectal gliosis secondary to an ingrowth of fibrillary glia and aquedectal stenisis secondary septum has been described. Aquedctal stenosis can also be inherited in the rare Bickers-Adams syndrome (X linked hydrocephalus).

Chiari malformation is frequently associated with aquedect stenosis, probably due to compression, dorasal displacement, and angulation of the aquedect.

Intraventricular hemorrhage(IVH) is the most common serious neurological complication of the premature infant. 35-70% of the preterm underwieght infants sustain IVH.

The hemorrhage develops from the germinal matrix capillaries that have not fully developed and are readily susceptible to damage. The flow distribution to the germinal matrix leads to a disproportionate cerebral blood flow in the periventricular circulation during the period of greatest susceptibility. The caudate nucleus and the cerebral cortex have high flow; the subjacent germinal matrix has low flow. Hypotension followed by rapid volume reexpansion is frequently the clinical context for hemorrhage.

The hemorrhage usually occurs within 48 hours of birth and occurs in the first 24 hours in 50% of cases. A later onset is not uncommon.

Post hemorrhagic hydrocephalus usually occurs in the first to the third week after hemorrhage. 20-50% of them develop hydrocephalus, either transient or progressive and about 50% of them may require surgical intervention.

Postnatal hydrocephalus:

Benign communicating hydrocephalus: 

It is also known as Idiopathic External hydrocephalus. It is characterized by rapid head growth, enlarged subarchnoid spaces with little or no ventriculomegaly. The pathogenesis is not clear.

Cephalomegaly above 90th percentile with normal neurological examination are the principle features.

CT and MRI reveal bilateral extracerebral fluid collections, prominent sulci, normal ventricles, and no evidence of compression of the brain. Chronic subdural hematomas must be ruled out.

The natural history is one of gradual resolution of the fluid collection. The family may be advised to avoid prolonged supine positioning.

Hydrocephalus in adults:

Aquedect stenosis, a developmental anomaly, may present in adulthood as well.

Hydrocephalus in adults are more commonly due to obstruction due to intracranial mass lesion or due to post infection, SAH, or trauma. They are discussed in appropriate sections. History of any intracranial procedure may be cause in some.

Normal pressure hydrocephalus is discussed elsewhere.

INVESTIGATIONS:

Skull radiographs reveal sutural separation. Periventricular calcifications in infants indicate in utero cytomegalovirus infection and disseminated calcifications indicate toxoplasmosis. The inion is typically low in children with aquedect stenisis, and high in Dandy-walker malformation. In older children, there may be copper beaten appearence or sellar enlargement which are nonspecific.

Cranial ultrasonography through the anterior fontanelle in infants can be particularly useful for serial evaluations after intraventricular hemorrhage. It also demonstrates ventricular morphology, and masses.

CT and MRI clearly demonstrate the hydrocephalus and the associated pathologies. The findings that favor hydrocephalus include dilatation of the temporal horns, enlargement of the anterior or posterior recesses of the third ventricle, narrowing of the mamillopontine distance, narrowing of the ventricular angle, widening of the frontal horn radius, and effacement of the cortical sulci. The most reliable parameter is the dilatation of the temporal horns.

Isotope studies and ICP monitoring helps to identify ventriculomegaly due to cerebral atrophy.

MANAGEMENT:

Medical treatment has been largely unsuccessful, at least in chronic and progressive cases. Diuretics may help in acute transient cases. Carbonic anhydrase inhibitor has been claimed to reduce CSF production. Adrenocorticosteroids may diminish the CSF flow.

Ventricular shunting:

In transient hydrocephalus, and in patients with high CSF protein or when CSF infection is suspected external ventricular drainage  is usually the first line of treatment. External drainage introperatively helps prior to certain tumor removal. Normally, the drainage is not maintained for longer than two weeks to avoid infection. Studies suggest that, if the drainage tube is tunneled well away from the insertion site, the infection rate is low.

Established and progressive hydrocephalus is treated with shunt insertion. Newborns with hydrocephalus with cerebral mantle less than<2cm, should be treated within 5 months to maximize the mantle thickness, associated with normal IQ.

The  shunts drain CSF from the ventricles to a site of of superior absorptive capacity. Many sites, including vessels, peritoneum, gall bladder, urinary bladder have been used. Peritoneum has been proven to have the best absorptive capacity. Ventriculo peritoneal, and  ventriculo atrial shunts are widely employed.

Implantable shunts are composed of a silicone elastomer and are often impregnated with barium. The shunts consists of a proximal catheter, a valve, and distal tubing. Evolution of shunts has been guided by the need to reduce the incidence of complications, some of which are trivial and self-limiting whereas others are occasionally fatal.  Financial aspects are also important, as an episode of shunt infection can be extremely expensive. Lately, antibiotic impreganated shunts are being marketed.

There is no perfect shunt. In general, there are three types of valves:

1) A pressure regulating valve opens at a preset pressure and maintains its pressure across the valve, regardless of flow rate.

Slit valves, e.g.. Hotler,Upadyaya, Chabra: flow decreases gradually as differential pressure decreases until closing pressure of valve (low pressure - 2-5cm water, medium pressure - 5-10cm water, high pressure - 10-15cm water) is reached.

Diaphragm valves, e.g.: Pudenz, Ceredrain: flow remains roughly constant until closing pressure is reached.

Ball valves, e.g.: Hakim: similar pattern to diaphragm valves.

Programmable valves allow the closing pressure to be adjusted externally using magnet.

2) Flow regulating valve maintains a constant flow at different pressures to overcome the complications of over drainage. The flow is regulated by increasing valve resistance as pressure increases.

3) Siphon resistant valves act by increasing the opening pressure of the system in direct proportion to the vertical distance between the proximal and distal ends of the distal tubing. This allows correction of hydrostatic pressure, which changes when the patient changes his position. Positive ICP is maintained, despite the position of the patient.

Insertion of a shunt must be regarded as a lifetime commitment from the surgeon to the patient. meticulous measures should be taken owing to the high frequency of potential complications. Small skin incisions to avoid contact with skin, small bony opening to prevent egress of CSF are recommended. The ideal position for the ventricular catheter is in the frontal horn or in the occipital horn to catheter blockage due to choroid plexus. The peritoneal catheter should be positioned over the liver in the retrohepatic space to avoid distal occlusion by omental fat.

Complications of shunts:

A baby with a new shunt would be expected on average to undergo 2 shunt revisions for blockage during first 10 years. Approximately 30% of infants with newly inserted shunts will have a shunt complication within the first year. 

The common shunt complications are, obstruction, over drainage, and infection, and less commonly, seizures.

Obstruction:

A shunt can occlude at any site, but the most common site is the ventricular end, usually by the choroid plexus.

The distal end can become occluded with fat and with an abdominal pseudocyst. Precise endoscopic placement of the ventricular end in the frontal horn to avoid the choroid plexus and abdominal end at the retrohepatic space may minimize the chance of obstruction.

RBCs, tumor cells, high protein level in CSF have also been the cause of proximal tube obstruction. Body growth, adhesions (associated with low-grade infection), and pregnancy may the cause in distal end.

A shunt  can occlude at any site, but the most common site is the ventricular end, usually by the choroid plexus. The distal end can become occluded with fat and with an abdominal pseudocyst. Precise endoscopic placement of the ventricular end in the frontal horn to avoid the choroid plexus and abdominal end at the retrohepatic space may minimize the chance of obstruction. Body growth, adhesions (associated with low-grade infection), and pregnancy may the cause in distal end obstruction.

Patient presents with features of raised ICT, and CT reveals ventriculomegaly.

If there is no spontaneous CSF flow through a needle inserted into the shunt reservoir, the proximal is the one that is blocked.

A shunt-o-gram, by injecting a radioisotope into the reservoir and imaging both ends, may help to detect the blocked end. ICP monitoring and CSF infusion studies will document more precisely the shunt’s hydrodynamic properties.

The blocked end may be revised. Alternatively, a new shunt system is established on the opposite side.

Overdrainage:

When there is excessive drainage, the ventricles may collapse around the shunt, as in the 'slit ventricle' syndrome. Siphoning effect of the shunt (hydrostatic pressure-25-75 cm CSF) caused by column of CSF within peritoneal or atrial catheter sucks fluid out of ventricles in upright position. Differential valve, even high pressure 15 cm CSF, may not stop siphoning.

'Slit ventricle' syndrome: Some patients will develop decreased transependymal flow and decreased intracranial compliance. When a shunt malfunction occurs in these patients, the ventricles fail to expand. Chronic low pressure within the ventricle and intermittent shunt malfunction due to ventricular catheter abutting against ventricular wall have been blamed

Clinical features include attacks of headaches, vomiting, drowsiness and pallor associated with slit-like ventricles on CT scan. 

It is a difficult problem to treat. Revision of shunt with a Siphon resistant valve, if available or a high pressure valve may help. Occasionally subtemporal decompression or other cranial expansion technique is needed.

Subdural Hematoma: Many post-operative sub dural collection are asymptomatic and do not require treatment.  Others may cause reduced conscious level and focal deficit, and require evacuation, and at times shunt removal and reinsertion of shunt with a Siphon resistant valve, if available or a high pressure valve as a second stage procedure.

Recurrent symptomatic sub dural collections may need sub duro-peritoneal shunt.

Infections:  

3-20% of the patients develop shunt infection, and have increased mortality and increased seizures and may affect long-term outcome in children. Staphylococcus epidermidis is the causative bacteria in two thirds of shunt infections. Staph. aureus and gram negative bacilli are also common. In neonates, Escherichia coli and Streptococcus hemolyticus predominate.

Presenting symptoms include nausea, vomiting, fever, lethargy, anorexia, irritability, and abdominal pain. In addition, shunt may get blocked with features of raised ICT. CSF cultures may be negative in 40% and one must have a high level of suspicion. On rare occasions, 'shunt nephritis' may develop, secondary to chronic low level infection of a shunt with subsequent immune complex deposition into renal glomeruli.

Strict aseptic precautions, and avoidance of  shunt surgery in the presence of CSF leak or intercurrent infection prevention.

In most cases of shunt infection, the shunt may need to be removed. External ventricular drainage may be required. Appropriate antibiotic is mandatory. Intravenous Vancomycin is used widely while awaiting bacteriological studies. Intrathecal/reservoir antibiotics do not provide additional benefit. When the CSF culture is sterile  for 3 consecutive days, it is recommended that the antibiotics may be continued for about 10 days and a fresh shunt  is inserted

Some centers are successful in treating shunt infections in situ without removing the shunt. 

Other rare complications:

Secondary sagittal synostosis may occur as a result of shunting in infants, particularly premature babies with severe post-hemorrhagic hydrocephalus.

Miscellaneous complications of V-P shunts (Operative misplacement of the shunt tubing, erosion of shunt tubing through wall of abdominal organs, disconnections) occur sporadically. 

Miscellaneous complications of V-A shunts (cardiac arrhythmias, cardiac tamponade, mural thrombus and pulmonary emboli, detachment of distal catheter during shunt revision) are uncommon, but more life-threatening than those in V-P shunts.

Endoscopic third ventriculostomy:

Internal decompression, by 'by passing' the obstruction, restores normal CSF flow. If the obstruction is in the ventricles or at the outlets of the third or fourth ventricles, internal decompression may be possible; third ventricle should not be small. The decrease in ventriculomegaly, is almost always less than that achieved after a V-P shunt.

Lately, internal decompression by rerouting CSF flow through the floor of the third ventricle using neuroendoscopic techniques has

become dramatically refined.Third ventriculostomy is claimed to be an effective alternative to shunt in experienced hands.

OUTCOME:

20% of untreated children survive to adulthood. Severely damaged babies with hydrocephalus are best treated by shunting to prevent excessive head growth and its associated nursing problems. 70% of babies with treated non tumoral hydrocephalus would be expected to attend a normal school, with a normal IQ. Most become shunt dependent and remain so for the rest of their lives.

About 50% of children with communicating hydrocephalus may retain the potential to be independent of shunt.