A prenatal ultrasound can sometimes reveal a choroid plexus cyst (CPC). While any unexpected finding can be unsettling, CPCs are relatively common. These fluid-filled sacs often resolve on their own and are frequently benign.
What Are Choroid Plexus Cysts?
Choroid plexus cysts are small, fluid-filled sacs that develop in the choroid plexus, a structure within the brain’s ventricles. The choroid plexus produces cerebrospinal fluid (CSF), which cushions the brain and spinal cord. These cysts are not considered brain abnormalities and do not affect brain function or development.
CPCs are a common finding during routine prenatal ultrasounds, particularly in the second trimester, occurring in approximately 1-2% of pregnancies. They are often temporary and typically disappear on their own by the third trimester, usually by 28 weeks of gestation.
The Link Between CPCs and Down Syndrome
Choroid plexus cysts are sometimes observed in fetuses with chromosomal conditions, including Down Syndrome (Trisomy 21). However, an isolated CPC, meaning no other “soft markers” are detected on the ultrasound, generally has minimal clinical significance for Down Syndrome. The vast majority of fetuses with an isolated CPC do not have Down Syndrome.
The risk of Down Syndrome with an isolated CPC is very low, often similar to the general population’s background risk. Studies indicate that the likelihood of Trisomy 21 is not significantly increased with an isolated CPC.
When CPCs Are Not Isolated
The significance of a choroid plexus cyst changes when identified alongside other “soft markers” or major structural anomalies during an ultrasound examination. These additional findings can increase concerns for chromosomal abnormalities, such as Down Syndrome (Trisomy 21) or Trisomy 18 (Edwards Syndrome). Trisomy 18 is a serious condition often associated with multiple birth defects and a low survival rate.
Examples of other soft markers that, when present with a CPC, might prompt further investigation include nuchal fold thickening, heart defects, kidney abnormalities, echogenic bowel, short long bones, or ventriculomegaly. It is the combination of multiple ultrasound findings, rather than an isolated CPC, that raises the likelihood of an underlying chromosomal condition.
Recommended Next Steps
Upon detection of a choroid plexus cyst, healthcare providers typically recommend a detailed, targeted ultrasound, sometimes referred to as a Level II ultrasound. This specialized scan aims to thoroughly examine the fetus for any other soft markers or structural anomalies. If the CPC is isolated and no other concerns are identified, additional testing may not be necessary.
Genetic counseling is often offered to discuss the findings, assess individual risk factors, and explore available testing options. Non-invasive prenatal testing (NIPT), which screens for common chromosomal conditions like Trisomy 21, Trisomy 18, and Trisomy 13 using a maternal blood sample, may be recommended. For a definitive diagnosis, more invasive procedures such as amniocentesis or chorionic villus sampling (CVS) can be considered, though these carry a small risk of complications, including miscarriage.