Located on the left and the right side of the brain, the choroid plexus is a gland that produces cerebrospinal fluid. This fluid bathes and protects the brain and spinal column. In 1 to 2% of babies, a cyst- a small round fluid filled area- is formed in the choroid plexus.
The exact cause of choroid plexus cyst is unknown. It is a collection of fluid, like a blister and not an abnormality of the brain matter itself.
Chromosomes are where most of our genetic information is kept. We usually have 46 of them matched in pairs: 23 come from one parent and the other 23 come from the other parent. For example, people with Trisomy 18 have an extra chromosome number 18. There have been reports associating a choroid plexus cyst with Trisomy 18. Fetuses with trisomy 18 have choroid plexus cysts about one third of the time. In fetuses with choroid plexus cysts, 2.1% have an abnormal number of chromosomes, with the majority having other anomalies that can be seen on the ultrasound. However, when no other anomalies are seen on the ultrasound, the risk of a change in the number of chromosomes is still around 1 in 300.
You will usually have a detailed ultrasound examination of the fetus to check if any other abnormality exists. In absence of any other abnormality, in most situations, no further tests are necessary. You midwife or doctor will be able to help you decide. If an additional abnormality is found, you will likely be offered a test to get more information about the chromosomes of the fetus. This could be a non-invasive prenatal test (NIPT) or an amniocentesis, depending on what is available and your choice.
An isolated finding of a choroid plexus cyst does not alter the management of pregnancy. Most of the cysts resolve by 28 weeks.
Studies evaluating outcomes in children with normal chromosomes born after prenatal diagnosis of choroid plexus cysts have not shown any differences in brain function, motor function or behaviour. Therefore, no postnatal evaluation is necessary.
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Last updated September 2018
