A patients guide to fetalVentriculomegaly
Introduction
Inside our brain there are four fluid filled spaces called ventricles. The two lateral ventricles are situated one in each half. During the mid pregnancy scan it is now routine to measure the width of these fluid filled spaces and to record this measurement. There can be a wide variation in this measurement but we have put an arbitrary upper limit on this measurement of 10mm. Having a measurement of 10 or 11 mm is not therefore necessarily abnormal but is simply outside of our “normal” range. A good analogy is that a woman who is 6 foot tall is well outside of the normal range but being that height does not make her abnormal. However a ventriclemeasurement above 10mm can suggest that there may be a problem with your baby and as such you will be offered further investigations. This information sheet is designed to answer some of the questions that you might have.
How severe is the problem?
This is a difficult question to answer. There is not an absolute correlation between the measurement and the outcome however the closer the measurement is to 10mm the more likely the outcome will be normal. At least 95% of babies with a measurement of between 10 and 12mm in mid pregnancy will be absolutely fine.
If the measurement is above 15 mm then there is a significant chance of long term problems but even with very marked dilatation some babies will have a normal life.
A measurement of between 10-12 mm is called borderline ventriculomegaly. (ventriculomegaly is the medical term for big ventricles). 13-15 mm is moderate ventriculomegaly and above 15mm severe ventriculomegaly.
What happens next?
The first step is to confirm the findings. It is possible to artificially make the ventricles appear larger than they are by measuring in the wrong place or at a slightly odd angle. A repeat scan will therefore be arranged either in your own hospital or at a specialist centre. In addition, for some, the ventricles will change in size and therefore will be less than 10mm when repeated. If the measurement is again above 10mm you will be counselled about the meaning and offered further tests.
What does it mean?
This is also a difficult question to answer because it will depend on a number of factors. Three important points need to be addressed. The first is the size of the ventricle;the second is, isthis an isolated problem and third is thisa marker for a chromosome anomaly such as Down’s syndrome.
The long term outcome depends on all three points and therefore it will only be possible to provide advice for you as an individual when we have had the opportunity to assess each of the factors.
As a general rule the smaller the measurement the better the outlook.
Is there a risk of Down’s syndrome?
The finding of a ventricle size above 10mm carries a risk of not only Downs’s syndrome but other chromosome anomalies. The risk is between 1-5%. Although this may sound like a high risk it also means that in 95-99% of cases the chromosomes will be normal.
What will happen when I am next seen?
A further scan will be performed to look very carefully at your whole baby including repeating the measurements of the ventricles. It is not possible to pick up all anomalies on ultrasound but we will obviously do our best. After that we will discuss the findings and if the ventricles are enlarged offer further testing.
What further tests will I be offered?
As stated above this finding carries a risk of a chromosome problem and as such you will be offered the opportunity of having this checked. This means having an amniocenteisis or a chorionic villus biopsy. Both of these carry a small risk of inducing a miscarriage and as such it is your choice as to whether or not you wish to have this done. Sometimes a viral infection in the mother can be passed to the baby in utero and can give rise to this problem. We can check this by taking a blood sample from the mother or in some cases by sending the fluid from around the baby for further testing. Finally we usually like to arrange for a further special scan called an MRI. This test is usually carried out in a different hospital, and often means travelling to Sheffield. MRI gives a different image of the fetal brain and has been shown to be better than ultrasound in detecting other abnormalities within the brain.
What are my options?
Once we have all the information from our ultrasound assessment and if performed the results of any further tests we will be able to give you a more definite answer as to what we feel it all means. Please be aware this may take a couple of weeks. In the majority of cases we will be very positive as to the outlook for the child, particularly if the finding is isolated and the ventriculomegaly borderline and non-progressive. Unfortunately, if the ventriculomegaly is progressive or severe then prognosis is less good. In this circumstance the some couples may opt for a termination of pregnancy. The issues around this will be discussed at length and we will support you in whatever decision you make.
Remember for the majority of babies this is almost certainly a normal finding and as such of little or no consequence.
Gerald Mason Leeds Fetal Medicine 05/07