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Nuchal Cysts (cysts in the fetus' neck)
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What is this and what is its significance?
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Small cysts in the sides of the fetus's neck are usually the result of a delay in
the formation of the blood vessels that drain the lymphatic fluid. It occurs in
about 1% of pregnancies. When it appears in the first trimester of pregnancy, it
usually resolves without any clinical significance for the fetus.
Cysts on both sides of the neck are of no clinical significance and have no detrimental
effects. According to a number of studies, the cyst can be used as a marker with
statistical significance only in chromosome defects such as trisomy 21 (Down syndrome), but this correlation is currently
considered weak and not statistically significant.
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The cyst as part of a group of parameters for evaluating the statistical risk for
chromosome disorders
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There are several parameters that establish the statistical probability for Down
syndrome, so that the presence of a cyst can be considered as part of the aggregate
of these parameters. Normal
nuchal translucency, young maternal age, absence of other signs or defects
on ultrasonography, and a normal biochemical screening result are all
factors that indicate a significantly reduced risk for Down syndrome.
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What should be done if this is diagnosed?
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Opinions differ
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Amniocentesis
(or chorionic
villus sampling) is undoubtedly the only test that can categorically rule
out chromosome
disorders. However, it is neither medically indicated nor recommended that
every pregnant woman should undergo amniocentesis - only those who are at high risk
of having a specific problem that can be examined by this test (see information
sheet titled: Why
is there no medical recommendation for amniocentesis in all cases?).
Most opinions hold that in the majority of the cases in which the cyst is the sole
finding, and taking into account the other parameters mentioned above, which do
not raise the risk for a chromosome disorder, the weighted risk is not in the high-risk
range for which amniocentesis is indicated. However, it should be noted that at
the present time there are no accurate statistical data that allow for a precise
calculation of the weighted risk taking the results of all the tests into account.
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Practical advice
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The "gold-standard" threshold for recommendation of amniocentesis is a risk of Down
syndrome greater than 1:386 based on the results of the biochemical marker screening
tests, and when the weighted risk is equal to or higher than this, amniocentesis
is generally recommended. However, the presence of nuchal cysts in the fetus may
statistically increase the risk of Down syndrome. Therefore in these cases some
physicians suggest that this should be integrated with the results of the biochemical
screening tests and the new threshold for recommending amniocentesis is a risk for
Down syndrome of greater than 1:1000 in the biochemical marker screening tests.
If other abnormal findings are also present, these guidelines are insufficiently
established and the woman should be referred for genetic counseling. In genetic
counseling, the necessity for amniocentesis can be assessed. It is important to
recommend counseling in all cases where other signs or defects are present, in cases
where the cyst is at the front of the neck (because this presents a slightly increased
risk for problems in the development of the hearing system, etc.), or if the cyst
is in the back of the neck as this indicates an increased risk for a chromosome
disorder. (See "nuchal
edema"). It is also worth considering referring the family for genetic counseling in cases where the cysts
are the sole finding.
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