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
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
Arrested hydrocephalus is an
asymptomatic condition with non-progressive ventriculomegaly.
Compensated hydrocephalus is a
symptomatic condition, with non progressive hydrocephalus.
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-
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
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
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
almost always results
obstruction (mechanical blockage or poor absorption) in the CSF pathways
and only rarely
overproduction of CSF, as in choroid plexus papilloma and
may be due to defective archnoidal villi or rarely, to raised venous
pressure as in sinus thrombosis.
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
head enlargement, dilated scalp veins, tense fontanelle, failure of
upward gaze, and 'sunset' sign; 'cracked pot' resonance of the skull (Macewen's
sign) may be detected in older children. Papilledema and 6th nerve
paresis may be Normal head circumference at birth is 33 to 36cm.
During the first year, it increases 2cm/month during the first 3
months; detected. 1cm/month from 4-6 months, and 0.5cm/month from 7 to
12 months. A diagnosis of hydrocephalus is indicated by circumference
increases across centile curves than by circumferences that are above,
but parallel to the 95%
Head circumference (CM)
standard head circumference in boys
of girls older than 3 months is 3cm smaller than that of boys.
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:
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
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.
About 80% of Myelomeningoceles and
encephaloceles also associated with hydrocephalus.
Approximately, 80% of the patients with
Dandy walker malformation
develop hydrocephalus in the first three months of life.
Hydrocephalus in Dandy walker malformation is, probably, due to
communication between the cyst and the subarchnoid space. Symptoms may
develop during the adolescent years.
Congenital toxoplasmosis, viral
infections, and cytomegalovirus can cause archnoiditis with
Other rare chromosome abnormalities
are associated with malformations, such as, agenesis of arachnoid
granulations, and foramen of Monro and hydrocephalus.
Hydrocephalus in preterm infants:
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.
Approximately 20% of cases of
hydrocephalus in children are related to a mass lesion, mostly
posterior fossa tumors. Tumors in the third ventricular region (craniopharyngioma,
intraventricular cysts, hypothalamic gliomas) can also cause
Vein of Galen malformation can compress
the aquedect and posterior third ventricle and cause hydrocephalus.
Other aneurysms and AVMs have been associated with obstructive
hydrocephalus depending on their location.
Various toxins viral infections, and
nutritional deficiencies have been implicated in the development of
hydrocephalus. Vit A, and B12 deficiency, folic acid deficiency, azo
dyes, lysergic acid diethylamide mescaline, triamicinolone acetamide,
irradiation, and methyl mercury have all been implicated .
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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
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.
pressure hydrocephalus is discussed elsewhere.
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.
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
studies and ICP monitoring helps to identify ventriculomegaly due to
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
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
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.
valves, e.g.: Pudenz, Ceredrain: flow remains roughly constant until
closing pressure is reached.
e.g.: Hakim: similar pattern to diaphragm valves.
valves allow the closing pressure to be adjusted externally using
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
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
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.
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
tumor cells, high protein level in CSF have also been the cause of
proximal tube obstruction.
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
A shunt-o-gram, by injecting a radioisotope
into the reservoir and imaging both ends, may help to detect the blocked
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.
When there is excessive drainage, the
ventricles may collapse around the shunt, as in the 'slit ventricle'
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.
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.
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.
of the patients develop shunt infection, and have increased mortality and
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
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
Strict aseptic precautions, and avoidance of
shunt surgery in the presence of CSF leak or intercurrent infection
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
Other rare complications:
Secondary sagittal synostosis may occur as a
result of shunting in infants,
particularly premature babies with severe post-hemorrhagic
complications of V-P shunts (Operative misplacement of the shunt tubing,
erosion of shunt tubing through wall of abdominal organs, disconnections)
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
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
become dramatically refined.Third
ventriculostomy is claimed to be an effective alternative to shunt in
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.
50% of children with communicating hydrocephalus may retain the potential
to be independent of shunt.