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Bilateral Ventriculomegaly Between 10 and 14 mm

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.

Dilation in excess of 14 mm is significant dilation, especially if there is an increase in the ventricular width from week to week. See information sheet: " Ventriculomegaly in excess of 14 mm and/or progressive ventriculomegaly - hydrocephalus".

The common causes for this type of ventriculomegaly are:

  • Obstruction 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 mother's 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.

What are the risks associated with mild ventriculomegaly when no other defects are found on ultrasound examination and no further expansion of the ventriculomegaly is detected on monitoring?

There is a risk for defects that affect the health of the fetus even when the ventriculomegaly is the sole finding on ultrasound examination. The risk is estimated to be approximately 23%. The defects include:

  • Defects that are undetectable by ultrasound examination in pregnancy but which may be detected at birth: 8.5%.

  • Chromosomal problems: 4%. These can be detected by amniocentesis. In most cases in which a chromosomal problem is detected, there are additional reasons for performing amniocentesis, such as advanced maternal age or increased risk for Down syndrome based on screening tests (biochemical screening or increased nuchal translucency). It is open to question whether a 35-year-old woman with normal screening test results that indicate a low risk for Down syndrome should undergo amniocentesis based solely on the presence of mild ventriculomegaly. It must be assumed that the risk for a chromosomal problem in this case is not very high, but because there is no definitive answer to this question, there is apparently an indication for amniocentesis that is not based solely on the presence of ventriculomegaly.

  • Developmental delay 12%. The risk is increased by the following criteria:
    A. It is more likely in girls (23%) than in boys (4%).
    B. It is more likely in ventriculomegaly in excess of 12 mm (14%) than of 10 - 12 mm (4%).
    C. It is more likely when the ventriculomegaly is first detected in the second trimester
    rather than late in the third.

It should be noted that follow-up studies of development in children born with mild ventriculomegaly have not been undertaken for long enough to know what the long-term consequences are. Therefore it is not known whether these children have learning difficulties or milder developmental disorders. The estimate is that the frequency of such disorders is slightly increased.

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 look for defects in the genitalia, eyes, heart and growth rate. Normal fetal movement should be ascertained. It is important to monitor the width of the ventricles, because sometimes the ventriculomegaly is unilateral, in which case the prognosis is better. It is also important to monitor the diameter of the head once every two to three weeks to ascertain that it is not expanding more than the normal amount.

  • Investigation for intrauterine infection should be carried out by testing the mother's 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.

  • Fetal echocardiography.

  • 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. As noted above, when there is mild ventriculomegaly, there is a definite indication to perform amniocentesis. Each case, however, must be considered individually, based on how important the pregnancy is, the week of gestation, the couple's wishes, the presence of other defects, the results of the screening tests for Down syndrome (biochemical screening and nuchal translucency), etc. These are discussed within genetic counseling. Based on the severity of the ventriculomegaly and the presence or absence of additional findings or a family history, further follow-up and molecular or other tests should be considered.

  • 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. The question of whether the result of an MRI scan can be normal and there still be a high risk for a developmental problem has been asked. It can be assumed that the risk in this case is lower than that described above, but there are no definitive answers to this question.
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Comments (4)

Friday, February 3, 2012 3:47 PM
(1) Patrice Wright  says:

mild ventriculomegaly in my 5 year old


Friday, February 3, 2012 3:47 PM
(2) Patrice Wright  says:

mild ventriculomegaly in my 5 year old


Friday, November 13, 2015 2:39 AM
(3) Matthew Lee  says:

Moderate to Severe Ventriculomegaly in the featus

My featus is diagnose with severe bilateral ventriculomegaly of 22.5 mm from 28 weeks of pregnancy. However, at the 33 weeks, the measurement have not increase neither has it been decreased. Could someone suggest the possible solution and findings for such situation?

Saturday, November 26, 2016 2:41 AM
(4) lavanya  says:

mild ventriculomegaly from 28 weeks

My featus is diagnose with bilateral vventriculomegaly of VP left 11 mm and Vp right 10.8 mm from 28 weeks of pregnancy. However it is not increased in next scan could someone give your answer if there any defects a raise in the baby development?

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