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Unilateral ventriculomegaly between 10 and 14 mm
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What is this and what is its significance?
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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?
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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?
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- 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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