A choroid plexus cyst is a buildup 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. There are no treatments for choroid plexus cysts. Most of the time, they go away on their own.
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 treatment.
The sex of your baby doesn’t affect your chances of getting a choroid plexus cyst. There may be some concern if a cyst appears to be unusually large. Your doctor may recommend that you have a more detailed ultrasound to check if there are any risks related to the choroid plexus cyst.
What Causes a Choroid Plexus Cyst in a Fetus?
“We’re not entirely sure what causes choroid plexus cysts,” says John Crawford, MD, medical director, neurology, and co-medical director of the CHOC Neuroscience Institute in Orange, California. “In many cases, these developmental remnants disappear towards the last trimester.”
What Are the Symptoms of a Choroid Plexus Cyst?
Choroid plexus cysts don’t cause any symptoms. “They’re usually found during the anatomical ultrasound,” says Crawford. This ultrasound is usually done around 20 weeks to measure the baby’s growth and development.
How Can You Identify a Choroid Plexus Cyst on an Ultrasound?
When an ultrasound is performed, the technologist takes photos and specific measurements of the fetus. When the radiologist reviews the images, they will notice a small, dark, round or oval spot in the choroid plexus. It’s usually about 2 or 3 millimeters.
How Are Choroid Plexus Cysts Diagnosed?
There are no tests to diagnose a choroid plexus cyst. The diagnosis is made based on what the radiologist sees on your ultrasound.
What Are the Risks of a Choroid Plexus Cyst?
Choroid plexus cysts are almost always benign and resolve on their own with time. Although rare, 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 such as their heart, kidneys, and brain. One-third of babies born with trisomy 18 have a detectable choroid plexus cyst.
Keep in mind that trisomy 18 is rare, affecting 1 in every 3,000 newborns. Most unborn babies who have a choroid plexus cyst don’t have trisomy 18. In cases where a baby does have trisomy 18, other abnormalities are usually found alongside a choroid plexus cyst. 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 tests such as
- Alpha-fetoprotein (AFP) test, which checks for possible DNA defects
- Amniocentesis, where amniotic fluid is removed from the uterus using a needle. The fluid is then tested to look for signs of genetic issues that may harm your baby's the health.
Experts don’t usually recommend an amniocentesis based on only a choroid plexus cyst. Possible risks that come with having an amniocentesis to detect trisomy 18 include:
- Leakage of amniotic fluid through the vagina
- Miscarriage (very low risk)
- Possible injury to the baby if they move their arms or legs when the needle is inserted
- The baby’s blood cells getting into the mother’s bloodstream
- Uterine infection
- Passing an infection from the mother to the baby
Expectant mothers should consider these issues when deciding whether to have 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 AFP test looks at the levels of a protein called alpha-fetoprotein (AFP) present in the mother’s blood. It can also rule out the potential of a baby having trisomy 18. The amount of AFP found can also help doctors recognize potential issues such as:
- Down syndrome
- Miscalculation of the mother’s due date
- The possibility of twins
- Abdominal wall birth defects in the baby
- Chromosomal abnormalities
- Open neural tube defects, such as 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 get results. Unlike with amniocentesis, there are no extra risks that come with having the test done. Doctors typically recommend the AFP test if they believe there is your unborn baby has a higher chance of having a congenital disorder.
If results from a level II sonogram and the AFP test don’t ease your concerns, an amniocentesis can help clarify the state of your baby’s health before its birth.
Studies suggest that children with a detectable choroid plexus cyst that went away did not have any ongoing cognitive issues. They tended to show behaviors, motor skills, and cognitive function of children without disabilities.
What Should Parents Know About Choroid Plexus Cyst Follow-Up and Testing?
Most choroid plexus cysts found during the anatomical ultrasound go away and can’t be seen in later ultrasounds.
According to Crawford, follow-ups aren’t usually done unless there’s a reason to believe there might be some other issue. “It really depends on the risk factors. If it’s an otherwise normal pregnancy and no other abnormal features — and a triple screen [blood test] is always performed to check for Down syndrome and neural tube defects, that's just standard,” he says. “So, if that’s abnormal, then that’s there’s other potential screening.”
Takeaways
About 2% of ultrasounds done to check on how well your baby is growing show a choroid plexus cyst, a small fluid-filled sac, in the brain. For the most part, these cysts disappear on their own and can’t be found in later ultrasounds. Babies with certain genetic disorders, such as trisomy 18, may be born with these cysts. But the cysts appearing on an ultrasound don’t mean the baby will have this or any other disorder. Your doctor will examine your risks to decide if you should have further testing.
Choroid Plexus Cysts FAQs
Are choroid plexus cysts related to autism?
Researchers are looking to see if there could be a link between choroid plexus cysts and autism. So far, they’ve found no evidence of a connection.
Do choroid plexus cysts affect brain development?
No, choroid plexus cysts don’t affect brain development.
Are choroid plexus cysts dangerous?
No, choroid plexus cysts aren’t dangerous. Almost all of them dissolve on their own before the end of the pregnancy.
