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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.

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Comments (1)

Tuesday, August 30, 2011 4:01 AM
(1) J  says:

unknown cyst? on neck of fetus

My son is a PA. His wife is pregnant and ultrasound shows the baby has something that extends from jaw/neck. He says that several physicians and PA's as well as the area's best obstetrician and ENT physician have studied the ultrasound and do not know what it is. They are scheduled for a "specialty ultrasound" at the medical university. The ultrasound that was already made seems fairly clear to me, and I can email that to you if you would consider looking at it.

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