Choroid plexus cysts (CPC's) are sometimes found on ultrasound scan at around 18-20 weeks gestation.

Before proceeding further it is important to understand why an ultrasound scan is offered at this time. Many people reply to this question with the answer that it is to see the baby. As well as this, the detailed scan at this time is directed at detecting abnormalities - that is, picking up significant problems that may or may not be compatible with life, problems that may require surgery once the baby is born or which might cause prolonged suffering or dependence into adult life.

Knowing about these major abnormalities gives parents the option of using this information in one of two ways. Either it allows them time to come to terms with these findings and prepare themselves for the baby's birth, or it gives an opportunity to consider if they wish to continue with the pregnancy. Many people choose termination of pregnancy in the presence of major abnormalities.

In addition to detecting major abnormalities, ultrasound sometimes detects 'soft markers' or findings which in themselves do the baby no harm, but may be associated with an increased risk of another abnormality. The presence of a soft marker is not diagnostic of this other abnormality, it is just a noted association in a number of cases.

CPC's are a soft marker for a gene abnormality called Edward syndrome.

The actual cysts themselves do not cause brain damage or other problems - ever.

What is Edward syndrome?
This is a gene abnormality where the baby has extra gene material of chromosome number 18. Down syndrome, by comparison, is when there is extra gene material of chromosome number 21 (also called trisomy 21). Edward or trisomy 18 is a serious condition, often associated with other structural abnormalities, such as heart defects in around 40% of babies. Many babies with trisomy 18 are stillborn before the end of pregnancy. Of those who are born alive, around half survive the first month of life, and 10% live to one year of age. Although serious ongoing problems are very common in survivors, successful surgery to correct heart abnormalities has taken place, and survival into late teens has been reported in around 10 affected people worldwide.

The gene problem happens most often just by bad luck, though is more likely in older women, and there is a rarer type of problem that runs in families. A mixed variation is known as mosaic, which is when half the body's genes are normal and half carry trisomy 18, leading to a less severe outlook.

So what is the risk of Edward syndrome?
If there are any other abnormalities detected on scan then the chance of Edward syndrome is high - around 1 in 3 - and a further diagnostic test to check is recommended. This may be amniocentesis or placental biopsy.

If there are no other abnormalities found on scan, then the risk of Edward syndrome is low - the individual risk is related to the woman's age. The table at the bottom of the page lists a woman's chance of having a baby with Edward's by both age alone and if there are CPC's found on scan. Thus, a 31 year old woman with a baby that has CPC's noted on scan has roughly a 1 in 264 chance that her baby has Edward syndrome. To put this into perspective, had this been her Down syndrome risk, she would not have screened positive.

How can I find out for sure if my baby is affected?
This involves a test to sample the baby's amniotic fluid (amniocentesis) or placenta (placental biopsy). Both involve a small needle being placed through the abdomen, which itself is not usually too uncomfortable. Both are carried out with ultrasound guidance. With amniocentesis a small amount of fluid is removed and the baby's skin cells are cultured. With the placental biopsy, some tissue is sampled. Occasionally there is a failure of the culture to grow (about 1/200) and it will need to be repeated. Amniocentesis takes about 11-14 days for a result, but placental biopsy only 48-72 hours. Very rarely the gene make-up of the placenta is not the same as the baby and a misleading result occurs.

The major drawback of both these diagnostic procedures is the associated risk of miscarriage. For amniocentesis there is an increased pregnancy loss rate of about 0.5% and for placental biopsy 1-2%. Of course when the risk of the condition causing concern is low, most of these miscarriages will be of normal (unaffected) pregnancies.

What is a high risk result?
Most people with a lower risk than 1/200 regard this as unlikely enough and do not ask for amniocentesis. Only you and your partner can decide if you feel that the chance of Edward syndrome is high enough to accept this procedure-related miscarriage risk. Some women faced with a 1/100 risk see it as a 99% chance of being normal and consider this as quite low. Others feel unsatisfied even with a 1/2000 chance. Some use the miscarriage risk as a guide and say that they'll have amniocentesis only if the risk of having an affected pregnancy is greater than the risk of miscarriage.

At the end of the day you have to live with the outcome of any decision. The loss of a baby through miscarriage at this late stage would be devastating, but some couples rationalise this possibility, and accept that the decisions must be made in good faith - particularly if the chance is higher. Some feel the risk of miscarriage of a normal pregnancy is just too much to take under any circumstance and that if the pregnancy is indeed affected, then nature will take its course. All are equally valid views.

What about the cysts themselves?
CPC's are very small and the risk of Edward syndrome seems to be no greater if they are large or small, one-sided or on both, persist later or not. Most cysts resolve by 24-28 weeks and a further scan may be arranged to reassure you of this. As mentioned above, the cysts do not cause brain damage or structural brain abnormalities. They are just a developmental 'phase' which passes. There are no implications for infant development or future intelligence.

Age	Age alone risk	CPC's present
20	1/4576	1/506
21	1/4514	1/499
22	1/4435	1/491
23	1/4333	1/479
24	1/4204	1/465
25	1/4045	1/447
26	1/3850	1/426
27	1/3619	1/400
28	1/3351	1/371
29	1/3050	1/337
30	1/2724	1/301
31	1/2385	1/264
32	1/2046	1/226
33	1/1721	1/190
34	1/1420	1/157
35	1/1152	1/127
36	1/921	1/102
37	1/727	1/80
38	1/567	1/63
39	1/439	1/49
40	1/338	1/37
41	1/258	1/29
42	1/197	1/22
43	1/149	1/16
44	1/113	1/l3
45	1/85	1/9

 

A medical article about a 23 year old woman who was found to have CPCs on her second trimester scan and what happened.

More information about Edward syndrome can be found on the Support Organisation for Trisomy (SOFT) page at: www.trisomy.org

Danny Tucker
Obstetrician and Gynaecologist