What is a Choroid Plexus Cyst?

A choroid plexus cyst is a build-up of fluid found in the choroid section of an unborn baby’s brain. It’s estimated that choroid plexus cysts happen in about 2% of pregnancies, usually during the second trimester. The choroid plexus consists of a network of cells and blood vessels found in various fluid-filled spaces in the brain, called ventricles. A thin layer of cells covers each of those vessels. These cells are in charge of making cerebrospinal fluid.

What Happens to Choroid Plexus Cysts?

Choroid plexus cysts are often found during an ultrasound. They occur when a small bubble of fluid breaks away as the choroid plexus forms. The cysts aren’t considered to be abnormal. Most choroid plexus cysts clear up without requiring further medical intervention.

The sex of your baby doesn’t change the likelihood of a choroid plexus cyst developing. There may be some concern if a cyst appears to be unusually large or found near the front of the baby’s body. Your doctor may recommend that you have a more detailed ultrasound to determine if there are any risks associated with the choroid plexus cyst.

What are the Risks of a Choroid Plexus Cyst?

When a doctor discovers a choroid plexus cyst, their most immediate concern is the possibility of the baby having trisomy 18, a genetic condition. Babies with trisomy 18 have an extra copy of chromosome number 18. Most of the time, a baby confirmed to have trisomy 18 is stillborn. Those who survive birth rarely live beyond infancy.

Babies born with trisomy 18 often have severe intellectual disabilities and problems with organs like their heart, kidneys, and brain. One-third of babies born with trisomy 18 have a detectable choroid plexus cyst. That’s why doctors prefer to take a closer look at the cysts. An additional scan gives doctors a better view of the cysts and helps them detect other anomalies.

Keep in mind that trisomy 18 is rare, occurring in 1 in every 3,000 newborns. Most unborn babies who have a choroid plexus cyst do not end up with trisomy 18. There are often other detectable issues found alongside a choroid plexus cyst in cases where a baby does have trisomy 18. If these abnormalities aren’t discovered during a second ultrasound, then it’s unlikely that the baby has trisomy 18.


How is a Choroid Plexus Cyst Treated?

There’s no way to treat a choroid plexus cyst. If you’re concerned about the possibility of your unborn baby having trisomy 18, you can ask your doctor about performing a test called amniocentesis. It’s a procedure where amniotic fluid is removed from the uterus using a needle. Your doctor will have tests run on the liquid to look for signs of genetic issues that may impact the health of your baby.

Possible risks that come with having an amniocentesis to detect trisomy 18 include:

  • Amniotic fluid leak through the vagina
  • Miscarriage, although the risk is very low
  • Injury to the baby when the needle is inserted, if they move their arms or legs during the procedure
  • The baby’s blood cells getting into the mother’s bloodstream
  • Uterine infection
  • Transmitting an infection from mother to baby

Expectant mothers should consider these issues when deciding whether to go through with amniocentesis. Even if the cyst goes away, there is still a possibility that the baby does have trisomy 18. Choroid plexus cysts almost always resolve in infants, even if the chromosomal anomaly exists.

An alpha fetoprotein (AFP) test, which looks at the levels of the protein present in the mother’s blood, can also rule out the potential of a baby having trisomy 18. The amount of AFP found can also help doctors recognize potential issues like: 

  • Down syndrome
  • Miscalculations in a pregnant mother’s due date
  • Possibility of twins
  • Abdominal wall birth defects in the baby
  • Chromosomal abnormalities
  • Open neural tube defects like spina bifida and anencephaly

The AFP test is typically performed anywhere between the 15th and 20th week of pregnancy. It usually takes about one to two weeks to receive results. Unlike with amniocentesis, there are no additional risks that come with having the test done. Doctors typically recommend the AFP test if they believe there is an increased likelihood of your unborn baby having a congenital disorder.

If the combination of a level II sonogram and the AFP test don’t alleviate your worries, then the amniocentesis can help clarify the state of your baby’s health before its birth.

Studies done on children with a detectable choroid plexus cyst that cleared up did not show any ongoing cognitive issues. They tended to show behaviors, motor skills, and cognitive function of children without disabilities.

WebMD Medical Reference Reviewed by Dan Brennan, MD on April 19, 2021



Journal of Obstetrics and Gynecology in India: “Prenatal Diagnosis of Choroid Plexus Cyst: What Next?”

Mayo Clinic: “Amniocentesis.”

National Cancer Institute: “Choroid Plexus.”

Society for Maternal Fetal Medicine: “Isolated fetal choroid plexus cysts.”

Stanford Children’s Health: “Alpha-fetoprotein (AFP) Screening Test.”

USCF Health: “FAQ: Choroid Plexus Cysts.”

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