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Nuchal Edema (Thickened Nape) and/or Cystic Hygroma

What is this and what is its significance?

This is edema of the fetus's neck caused by an accumulation of fluid, usually lymph. Usually lymphatic fluid collects at this site and is absorbed into the bloodstream. However, a delay in the development of the system that drains the fluid into the blood can result in an accumulation of superfluous fluid known as edema - this usually resolves with the completion of the development of the lymph drainage system. In cases of very marked edema, it resolves only at a later stage, and may leave a surplus of skin in the fetus's nape. In extreme cases, this surplus skin can be seen at birth by a pediatrician (parents will not notice it because it is not a very prominent sign).

The edema is significant if it covers the back and sides of the neck with more than 3 mm thickness up to week 14 of gestation, and more than 4 - 5 mm later. A thickening of the nape without edema of more than 5 or 6 mm between the 14th and 16th week of gestation is considered to be abnormal.

In some cases this is a transient finding without clinical significance, but in most cases it indicates a significant risk for a fetal disorder. The more marked the edema (or the thicker the nape), the greater the risk for the fetus. The edema itself does not have clinical significance, but it constitutes an indication for an increased risk of fetal problems.

The common causes of nuchal edema are:

  1. A chromosome disorder in the fetus. Many studies have reported a significant correlation between nuchal edema and chromosome disorders, especially Turner syndrome and Down syndrome. Different reports quote risks of 18% if the edema is an isolated finding and 33% if there are additional defects.

  2. Heart defects. In a significant percentage of cases in which there is significant edema, heart defects are diagnosed in fetal echocardiography.

  3. The onset of diffuse fetal edema (hydrops).

  4. Intrauterine infection by a virus or other pathogen. Common viruses such as CMV may cause cervical edema as part of the general picture of infection in the fetus.

Once these conditions have been ruled out, the risk for the presence of other defects and syndromes depends on the severity (the excess over 3 mm) of the edema/thickening. Usually, even when there is a significant degree of edema (see cystic hygroma below), the additional risk is only 3% - 4% higher than the regular risk.

If the edema is of moderate or severe degree, there is an increased risk of other defects or syndromes that cannot all be detected in additional tests. These include very short stature and many other conditions. In the case of translucency/edema in excess of 6 mm, the risk that a syndrome or other defects may be detected later is especially high, even in the absence of a chromosome disorder.

What should be done if this is diagnosed?

Genetic counseling should be offered so that the parents can receive a thorough explanation of its significance and to discuss whether further monitoring and investigation, particularly amniocentesis, is necessary. Counseling is especially important in the presence of additional defects. In such cases it is also important to refer the family for multidisciplinary counseling after ruling out other problems such as chromosome disorders, additional defects and maternal infection. This is because there is still a risk that the fetus might have a genetic syndrome even if the results of all the tests are normal.

Echocardiography should be performed between the 22nd and the 24th week of gestation. This can detect severe defects at a relatively high level of confidence.

A 3rd level ultrasound scan, directed mainly at the heart and nape, should be performed between the 15th and the 16th week and again between the 22nd and the 24th week of gestation. This is in order to look for additional defects and diffuse fetal edema.

The mother's blood should be tested for antibodies against common pathogens that may infect and damage the fetus (TORCH organisms), and also for a virus associated with fetal edema called Parvo-virus. If antibodies are found and the level and type raise concern that there has been a maternal infection, tests should be carried out to identify the virus/bacterium in the amniotic fluid.

What is cystic hygroma?

In more severe cases there may be a significant pooling of fluid in the nape, forming a cyst of lymphatic fluid known as a cystic hygroma. There are two types of cysts with differing clinical significance with regard to severity. One is known as a septated cystic hygroma, and the other is a non-septated cystic hygroma. In the former, the cysts are more structured and prominent, and the risk for chromosome disorders is much higher than it is in the non-septated type. Various studies have reported the presence of chromosome disorders in 50% - 90% of affected fetuses. The wide range is because of unclear definitions of the type of cyst and a lack of separation between cases identified in the first and second trimesters of gestation. When a cyst is identified in the first trimester of pregnancy, the most common chromosome disorder is Turner syndrome (45, XO). In the second trimester such chromosome disorders as Down syndrome and trisomy 18 etc. are more common.

It is important to note that even in cases where the cyst is reabsorbed, a chromosome disorder in the fetus cannot be ruled out because in most cases where a fetus has Down syndrome there are small cysts in the neck, which spontaneously disappear between the 15th and the 16th week of gestation.

In addition to chromosome disorders it is important to look for all the above-mentioned conditions including fetal heart defects and the onset of diffuse edema in the fetus.

As already mentioned, there is an increased risk for fetal defects and genetic syndromes even if the results of all the tests, including amniocentesis, are normal. In typical cystic hygroma, the risk remaining after completing all the tests, even when all the results are normal, is 15% - 30% for syndromes involving developmental delay.
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Comments (1)

Tuesday, March 20, 2018 10:40 PM
(1) valentina son  says:

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