|
|
|
Nuchal Cysts (cysts in the fetus' neck) |
|
|
What is this and what is its significance? |
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.
|
The cyst as part of a group of parameters for evaluating the statistical risk for
chromosome disorders |
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.
|
What should be done if this is diagnosed? |
|
Opinions differ |
|
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.
|
Practical advice |
|
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.
|
|
|