A choroid plexus cyst (CPC) is a common finding during prenatal ultrasounds, often appearing as a small fluid-filled sac within an unborn baby’s brain. These cysts are detected in approximately 1% to 2% of pregnancies, typically during the second trimester. In most instances, choroid plexus cysts are considered a normal variation in development and are not dangerous, frequently resolving on their own before birth.
Understanding Choroid Plexus Cysts
The choroid plexus is a specialized tissue located within the fluid-filled spaces of the brain, known as ventricles. Its function involves producing cerebrospinal fluid, which helps cushion and protect the brain and spinal cord. A choroid plexus cyst forms when a small amount of this fluid becomes trapped within the developing choroid plexus, resembling a tiny blister.
These cysts are identified during prenatal ultrasound examinations, particularly between 16 and 24 weeks of gestation. They can vary in size, shape, and number, appearing on one or both sides of the brain.
Assessing the Risk
Isolated choroid plexus cysts, meaning those found without any other detected abnormalities, are considered benign findings. These cysts often disappear spontaneously by the third trimester, around 28 to 32 weeks of pregnancy.
In some cases, choroid plexus cysts can be considered a “soft marker” for certain chromosomal conditions, such as Trisomy 18 (Edwards Syndrome). This association is relevant when other structural abnormalities or risk factors are also present. An isolated CPC has a low predictive value for these conditions, with the risk of Trisomy 18 being less than 1% when no other markers are found. CPCs do not increase the risk for Down syndrome (Trisomy 21).
Next Steps After Diagnosis
Upon discovery of a choroid plexus cyst, medical professionals recommend a detailed ultrasound examination. This comprehensive scan aims to identify any other “hard” or “soft” markers that might suggest an underlying chromosomal anomaly. If the choroid plexus cyst is an isolated finding with no other concerns, further action may not be necessary.
Follow-up ultrasounds may be suggested to monitor the cyst’s resolution, although for isolated CPCs, this is not required. Genetic counseling may be offered to discuss the implications and available testing options. Invasive testing, such as amniocentesis, is considered when additional risk factors or other ultrasound abnormalities are identified, not for an isolated CPC alone. The overall prognosis for pregnancies with isolated choroid plexus cysts is favorable, as they usually resolve without any impact on the baby’s health or development.