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Ventriculomegaly (mild dilation of the ventricles of the brain)


What is this and what is its significance?

On a cross-sectional scan using the ultrasound transducer it can be seen that the brain is divided into two hemispheres. Within each hemisphere there is a ventricle (cavity or chamber) that contains fluid that lines and protects the surrounding soft brain tissue. The fluid in the ventricles is produced by spongy tissue, known as the choroid plexus, that appears to float in the ventricular cavity. Mild ventriculomegaly is defined as dilation of the lateral ventricles of the brain that does not raise the intracranial pressure and does not increase from one scan to the next. In the second and third trimester, the normal width of the ventricle (including mild ventriculomegaly without significant mental handicap) is up to 10 mm. Dilation up to 14 mm is considered mild.

Borderline dilation

Ventriculomegaly (unilateral or bilateral) of up to 9 - 10 mm is not rare, and if it is an isolated finding, it is not associated with a significant increase in the risk for mental retardation. However, it is necessary to establish that:
  1. There are no other defects in the brain or elsewhere.

  2. No increase in the width of the ventricles beyond 9 - 10 mm is found on follow-up within 2 - 3 weeks.

  3. The fetuss head circumference is normal and corresponds with that of each of the parents, since a small head circumference in the presence of ventriculomegaly can indicate a small brain volume.

  4. There is normal fetal motility. The width of the ventricles must be monitored by ultrasound in order to rule out further, pathological dilation. It is, of course, also necessary to rule out intrauterine viral infection in the fetus as a possible cause of ventriculomegaly.

Ventriculomegaly of up to 9 - 10 mm is associated with an increased statistical risk of chromosome disorders, and based on the results of a number of studies, with albeit only a small number of pregnancies, this risk has been estimated to be approximately 1% - 5%. Because of this the genetic counselor may consider that it is worth recommending amniocentesis, taking into account the week of gestation, other test results, etc.

Mild ventriculomegaly

Ventriculomegaly is defined as mild when the width of the ventricles (unilateral or bilateral) is between 10 and 14 mm. The implications for the fetuss mental functioning are determined by the cause of the ventriculomegaly and by its severity and rate of progress. The most common causes of this type of ventriculomegaly are:
  • Blockage of the fluid passages out of the ventricles because of bleeding and the formation of a clot in the drainage outlets. The fluid formed in the ventricles then accumulates and results in ventriculomegaly with an increased head circumference.

  • Defects in the structure of the brain arising from genetic causes that may or may not be hereditary that disrupt the normal, complex development of the brain. In cases in which further defects are detected in the brain in particular and in other organs in general, there is an increased risk that the fetus may have a syndrome, with a significantly increased risk of mental retardation.

  • Environmental effects such as disrupted blood flow to the brain or infections (viral or other pathogen) during pregnancy. The mothers blood can be examined to test for infection by some of the common pathogens. If the cause is found to be a viral infection that is known to cause ventriculomegaly, there is, of course, an increased risk of fetal developmental retardation.

  • Chromosome disorders. If the ventriculomegaly is an isolated finding, the risk of an associated chromosome disorder is between 2% and 5%. However, the presence of other abnormal findings on ultrasound examination significantly raises the risk - according to some reports to as high as 25%. In these cases it is worth recommending that the mother undergo amniocentesis for chromosome analysis.

It is worth noting that apart from obstruction of the fluid passages, which usually leads to a larger than average head circumference, the other causes of ventriculomegaly tend to be associated with a decreased brain volume, and therefore a relatively small head circumference.

Risk of neurological problems in cases of mild ventriculomegaly (over 10 mm)


Even when ventriculomegaly is an isolated finding, there is nevertheless a risk of mental retardation and neurological problems. There are reports in the literature that the risk of neurological disorders, including mild ones such as learning problems, fine motor problems, etc., is approximately 20% - 30% in these children; however most of these disorders are not severe.

Obviously, there is a correlation with the extent of dilation. A study that divided patients with ventriculomegaly into two groups - those whose ventricles were between 11 and 12 mm in width and those whose ventricles were between 12.5 and 15 mm in width - showed that there was a significant difference between the two groups. The risk of retardation in the group with dilation up to 12 mm was only 3%, whereas the risk in the second group was significantly higher.

What should be done if mild ventriculomegaly is diagnosed?

  • A thorough ultrasound system scan should be carried out to look for additional defects in the structure of the brain or other organs. It is also important to monitor the width of the ventricles every two to three weeks in order to ascertain that it is not increasing.

  • Investigation for intrauterine infection should be carried out by testing the mothers blood in order to look specifically for the known teratogenic pathogens (agents that are known to infect and harm the fetus) such as TORCH, varicella-zoster virus, Epstein-Barr virus, etc.

  • Genetic counseling should be offered in order to give the parents a thorough explanation about the implications of the finding and to plan further follow-up such as whether it is advisable to undergo amniocentesis to rule out a chromosome disorder in the fetus. These decisions should be based on the severity of the ventriculomegaly and the presence of additional findings or a family history.

  • In cases of mild or more severe ventriculomegaly, it is advisable to refer the parents to a multidisciplinary clinic in a hospital for professional counseling by a pediatric neurologist, a geneticist, an expert in ultrasound examinations and a neonatologist, in order to collate all the data and discuss the various possibilities and courses of treatment that are available, etc. The decisions taken will depend on the severity of the problem, the presence of additional findings, etc.

In the last few years, high-speed MRI machines have been developed that enable examination of the fetal brain (this could not be done before because the fetus often moves and the older MRI machines were not quick enough). Cumulative experience shows that this test has a great advantage in identifying defects that cannot be detected by ultrasound, and it is recommended in cases of mild or more severe ventriculomegaly, especially when other defects are also present.

Hydrocephalus

This is an extreme state of ventriculomegaly with increased pressure on the brain tissue itself. Here there is a progressive dilation of the ventricles from week to week. It is caused by an obstruction in the canals or apertures of the brain, which results in increased accumulation of fluid in the ventricles. Usually this appears in the third trimester of pregnancy.

In some cases it is caused by bleeding and the formation of a clot that obstructs the outlets of the ventricles, and in other cases by a genetic defect that is more common in males. If other defects are also present, the cause may be genetic and more complex, such as a chromosome disorder.

This condition can have major implications for the mental functioning of the fetus, depending on the severity, the presence of additional defects, the cause of the hydrocephalus, gestational age, and the rate of progression of the dilation of the ventricles.

In cases of hydrocephalus, it is advisable to refer the parents to a multidisciplinary clinic in a hospital for professional counseling by a pediatric neurologist, a geneticist, an expert in ultrasound examinations and a neonatologist, in order to collate all the data and discuss the various possibilities and courses of treatment, etc., as well as whether any further tests, such as MRI and special DNA tests, should be carried out.
 
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Comments (3)


Friday, June 10, 2011 8:05 PM
(1) Nobuhle  says:


Ventriculomegaly of 9mm

I am on my 24th week, and on my 20th week I discovered that my unborn baby have Ventriculomegaly of 9mm. How severe is this? Will this cause brain damage or is everything going to be fine. Everything else on the baby is fine, but me and my fiance'are extremly worried as this our first baby...


Monday, August 08, 2011 6:24 AM
(2) nana salunke  says:


letaral ventricles 11.mm

I am on my 32 week, I discovered that my unborn baby have Ventriculomegaly of 11mm. How severe is this? Will this cause brain damage or is everything going to be fine. Everything else on the baby is fine, but me and my familly 'are extremly worried as this our first baby... Please reply me as soon as possible,really i am waiting for your reply.


Wednesday, May 15, 2013 9:32 AM
(3) ayesha  says:


bilateral lateral ventricles

i am 23 year old house wife. during my first pregnancy while having scan at 30th week, report says the bilateral lateral ventricles appear slightly dilated measuring 9mm and 9.5mm bilaterally. how severe is this? what damage it can cause to the brain or other systems of body of baby? during my previous scan at 20th week, no such case was discovered. everythingelse on the baby is fine. kindly advice me if everything is normal.





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