A choroid cyst is a small buildup of fluid in the choroid plexus, a structure in the brain which produces cerebrospinal fluid (CSF). Choroid cysts are most commonly identified as an ultrasound finding, and are in fact not uncommon, being seen in around one to three percent of fetuses. Adults can sometimes also have a choroid cyst, and be entirely unaware of it, although it will show up in detailed imaging studies of the brain as a small bubble of fluid.
Also known as a choroid plexus cyst, a choroid cyst is not harmful, although it might sound frightening, since the words “cyst” and “brain” are generally not ones which people like to hear used in the same sentence. In fetuses, they are usually identified during a second trimester ultrasound, and they often resolve independently by 28 weeks. These cysts usually form due to benign abnormalities which occur during development, and have no impact on the formation of the brain.
The issue with a choroid cyst is that it can be associated with genetic abnormalities, most commonly trisomy 18. Having a choroid cyst does not mean that a fetus has a genetic abnormality, but it can be a warning sign when combined with other factors. If an expecting mother is under 35, in good health, and at no obvious risk, a doctor may not counsel any additional action, beyond monitoring the choroid cyst and the development of the fetus with routine ultrasounds.
If a doctor feels that a fetus may be at risk for abnormalities, a more detailed ultrasound to collect more information may be recommended. The possibility of an amniocentesis may also be discussed. Patients should be aware that there are certain risks to an amniocentesis which should be weighed before getting the procedure. A doctor can provide more information about the risks and benefits of the procedure, and may refer parents to a genetic counselor so that they can talk about possible findings and their implications.
The important thing to remember if a doctor identifies a choroid cyst during pregnancy is that the fetus may be perfectly healthy, and the cyst will probably resolve on its own. While a choroid cyst can be an indicator of a problem with the fetus, parents should avoid jumping to conclusions about the finding. Discussing options with a doctor before making any decisions about whether or not to pursue additional testing is an excellent idea.