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CAR: Anomalies - CNS

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Introduction Antenatal Postnatal West Midlands Data



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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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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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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© Perinatal Institute 2011