INTRODUCTION
Hydrocephalus literally means water in the head, but the medical meaning of
this word is an abnormal increase in the volume of the cerebral ventricles
compared with brain tissue. The upper brain is separated into two cerebral
hemispheres each containing a fluid filled space, called the lateral ventricles.
The cerebrospinal fluid (CSF) is produced by the choroid plexus and flows
through the cerebral aqueduct to reach the fourth ventricle and down into
the spinal cord from where it is re-absorbed. Most cases of congenital (obstructive
or non-communicating) hydrocephalus are caused by a disturbance in the flow
of CSF, usually due to an obstruction, causing an increase in intracranial
pressure. The third and lateral ventricles are swollen with fluid, the cerebral
cortex is abnormally thin, and the sutures of the skull are forced apart.
Hydrocephalus is rarely due to an increase in CSF production (from choroid
plexus tumours) or a decrease in amount of brain tissue.
Hydrocephalus may arise from a number of causes, these include:
- Cerebral malformations - e.g. Arnold Chiari.
Hydrocephalus is commonly associated with meningomyelocele
(spina bifida) which interrupts the flow of CSF.
- Obstructive masses
- An over production of CSF - choroid plexus tumours
- Post haemorrhage - following a premature delivery
- Infection - toxoplasmosis (established through
maternal serology)
- X linked congenital hydrocephalus - this condition
is X linked and hydrocephalus is caused by aqueduct
stenosis, affected males have thumbs flexed over
palm.
Various trisomy conditions can cause
hydrocephalus and if multiple anomalies are present
an abnormal karyotype is highly likely, but even
in isolated hydrocephalus, the risk is high enough
to consider karyotyping.
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ANTENATAL
At 20 weeks gestation when many fetal anomaly scans
are performed the lateral ventricles can be easily
seen, and assessed. The lateral ventricles can be
assessed for hydrocephalus on ultrasound from around
16 weeks gestation, although the diagnosis of hydrocephalus
becomes easier with the development of the fetal
brain over the following 4 weeks. If hydrocephalus
presents later in pregnancy, other causes, such as
intracranial haemorrhage in utero, should be considered.
The ventricle has an anterior and posterior extension,
either or both of which may be enlarged. The measurement
across the ventricle should be no more than 10 mm,
and the choroid plexus which normal runs along the
medial wall of the ventricle should not dangle down
more than 3 mm from the medical border.
When the abnormality involves the whole of the
ventricle both anterior and posterior horns are dilated,
with the choroid plexus dangling down, and often
seen floating during the scan. The association with
spina bifida is well established and leads to careful
assessment of the rest of the brain tissue, particularly
the cerebellum, and the spine itself.
If no other abnormalities are found the term isolated
hydrocephalus is used. Gross hydrocephalus will lead
to flattening of the white and grey matter of the
cerebral ventricles and affects normal brain function.
The degree of functional loss can be difficult to
predict with precision, but in general terms those
cases which appear severe in mid-pregnancy are likely
to become worse during the pregnancy and will tend
to have poor outcomes.
When one part of the lateral ventricle, usually the posterior horn, is enlarged
this is termed ventriculomegaly. The implication is that this is a relatively
minor degree of dilatation, and there is little information about the precise
implications of this finding. There are reports that this may be a marker for
Down's syndrome, although the level of increased risk is poorly defined. The
other question is whether this finding has any major significance in relationship
to learning difficulties and developmental delay. It is quite clear that the
majority of cases have completely normal outcomes, but whether or not there
is an increased chance of problems with development is very difficult to discover.
If the head circumference is above the 97th centile
at term there is a high risk of obstructed labour.
Management options include drainage of the fluid
from the fetal head (cephalocentesis), or elective
caesarean section. Even at caesarean section the
head may prove difficult to deliver, but cephalocentesis
prior to delivery is often associated with a poor
outcome. Ventriculo-amniotic shunts, allowing the
excess of CFS from the fetal ventricular system to
vent into the amniotic cavity, have been used in-utero
with limited success.
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POSTNATAL
The most common treatment for hydrocephalus is
the use of shunt systems to divert CSF from the ventricles
to other sites. These have complication such as blockage
or infection but have improved the long term outcomes
of infants born with hydrocephalus. However if the
hydrocephalus is severe and other anomalies are present,
aggressive treatment may not be warranted.
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West Midlands Data
Information to follow
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