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Choroid Plexus Cyst

What is this?

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. This tissue actively secretes fluid. Sometimes it secretes the fluid into the spongy system itself, creating a fluid-filled cyst. This is one of the most common ultrasonic findings, appearing in about 1% - 2% of fetuses between the 16th and the 18th week of gestation. In about 90% of cases it resolves and disappears by the 28th week, and in other cases it resolves later. It sometimes occurs in both ventricles and sometimes only in one.

What is its significance?

The cyst itself is of no clinical significance - it is situated within the ventricular cavity and does not come into contact with the brain tissue. This means that the cyst has no detrimental effects.

According to a number of studies, the presence of a choroid plexus cyst is only of statistical significance for certain chromosome disorders such as trisomy 18.

In earlier studies a correlation with trisomy 21 (Down syndrome) was reported, but this correlation is currently considered statistically weaker and less significant than that with trisomy 18.

It is important to note that in most cases in which trisomy 18 has been diagnosed, other defects in addition to the choroid plexus cyst have also been found, and in only two cases of trisomy 18 reported in the literature was the cyst the only fetal finding.
When a choroid plexus cyst is associated with additional defects, the risk of a chromosome disorder in the fetus is estimated as being about 15%, whereas when it is an isolated finding, the risk is less than -%. The risks do not vary if the finding is unilateral or bilateral or with the size of the cyst.

The choroid plexus cyst as part of a group of parameters for evaluating the statistical risk for chromosome disorders

There are several parameters that determine the statistical probability for trisomy 18, so the presence of a choroid plexus 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 trisomy 18. The result of the biochemical screening test has parameters that allow for a statistical calculation of the risk of trisomy 18 - in some laboratories a specific calculation for this syndrome is made.

What should be done if this is diagnosed?

There are differing opinions. 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 choroid plexus 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.

For practical purposes:

A directed system ultrasound scan in order to look for additional defects associated with trisomy 18 should be performed in the 22nd week of pregnancy. If any other defects are found, then amniocentesis should be performed.

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 a choroid plexus cyst 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. Similarly amniocentesis is recommended if the risk of trisomy 18 is greater than 1:4000 rather than the usual 1:386. 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 particularly important to recommend counseling in all cases where other signs or defects are present, or if the cyst persists after the 28th week. It is also worth considering referring the family for genetic counseling in cases where the cyst is the sole finding.
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