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Unilateral ventriculomegaly between 10 and 14 mm |
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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.
See information sheet: Borderline ventriculomegaly (up to 10 mm).
Ventriculomegaly in the range of 10 – 14 mm is considered mild (see information sheets: Bilateral
ventriculomegaly of up to 14 mm and Unilateral ventriculomegaly of up to 14 mm).
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.
There are no major differences between unilateral and bilateral ventriculomegaly, but the unilateral
type is slightly more benign.
Ventriculomegaly in the range of 10 - 14 mm is considered mild and can be unilateral or bilateral.
The bilateral type is covered in the information sheet: Bilateral ventriculomegaly of up to 14 mm.
The discussion here is of unilateral ventriculomegaly, where there is asymmetry between the sizes of
the two ventricles, with one being at least 10 - 14 mm wide.
The common causes are:
- In some cases, it may be a variation of the norm.
- In a relatively small number of cases there may be unilateral obstruction of the fluid
passages out of the ventricle on one side because of bleeding and the formation of a clot in
the drainage outlet.
The fluid formed in the ventricle 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.
This is possible but has not been proved.
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 that is
usually bilateral, there is an increased risk of fetal developmental retardation.
- Chromosome disorders.
In cases where the ventriculomegaly is an isolated finding, the risk of an associated
chromosome disorder is 4%; however a more
careful analysis of cases indicates that the true risk is lower.
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 tend to be associated with a decreased brain
volume, and therefore a relatively small head circumference.
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What are the risks associated with mild unilateral ventriculomegaly? |
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In about 30% of cases, the ventriculomegaly is associated with other
defects in the brain or in other tissues, or with chromosome disorders or other anomalies.
In such cases, there is a high risk that the child will have a developmental
neurological problem and/or other problems.
It is therefore important to refer the family for genetic and other professional
counseling in order to discuss the ramifications of the condition and what the
future will hold.
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The risk for chromosomal problems is about 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 unilateral ventriculomegaly.
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What are the risks associated with mild unilateral ventriculomegaly when no other defects
are found on ultrasound examination and no further expansion of the ventriculomegaly is detected
on monitoring? |
In about a third of the cases, it resolves by birth. Most researchers agree that the risk for
developmental problems or convulsions after birth is not significantly higher than that in a regular
pregnancy.
The problem is that up to now too few cases have been described in the medical literature to be
able to estimate from these whether or not there is a slight increase in the risk for
convulsions (some of the patients had epilepsy) or developmental delay.
It should be noted that there is a risk of 3% – 5% for defects and mental retardation in each pregnancy.
Because follow-up studies of development in children born with mild unilateral ventriculomegaly have not
been undertaken for long enough to know what the long-term consequences are, it is not known whether
these children have learning difficulties or milder developmental disorders.
The estimate is that the frequency of such disorders is low, if it exists at all.
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What should be done if mild unilateral 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 and 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 in 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.
- 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
bilateral ventriculomegaly. For unilateral ventriculomegaly, in the absence of other defects
detected on ultrasound examination, it is not currently recommended that MRI be performed.
It can be done privately, however, but it should be kept in mind that it is on trial status in
these cases.
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