Obstetric ultrasound procedure with doctor scanning pregnant patient. Obstetric ultrasound procedure with doctor scanning pregnant patient.

What Causes Cysts in Fetal Brain?

Extra-axial cysts, mainly arachnoid cysts, are common in the fetal brain. These cysts are either primary or secondary. Primary arachnoid cysts, filled with cerebrospinal fluid, usually aren’t connected to the subarachnoid space. On the other hand, secondary arachnoid cysts, resulting from bleeding, injury, or infection, often connect to the subarachnoid space.

1. What are Choroid Plexus Cysts?

A choroid plexus cyst refers to an accumulation of fluid within the choroid region of an unborn baby’s brain, occurring in approximately 2% of pregnancies, predominantly in the second trimester.

These cysts develop within the choroid plexus—a network of cells and blood vessels in the ventricular system in fluid-filled spaces known as ventricles. It is responsible for producing cerebrospinal fluid, a thin layer of cells covers these vessels.

What Causes Cysts in Fetal Brain
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2. Diagnosing Arachnoid Cysts

Doctors usually find arachnoid cysts after 20 weeks of pregnancy using ultrasound. On the ultrasound, an arachnoid cyst might look like a clear, round, oval, or crescent moon-shaped mass at the back of the baby’s brain, and when an arachnoid cyst is seen, the doctor will conduct a detailed sonogram to ensure there are no other issues.

In some cases, a prenatal MRI may be needed. If other problems show up, the doctor might suggest amniocentesis to check for chromosomal or genetic issues. If the cyst is linked to a chromosomal problem, the mother and baby might also get genetic counseling.

The size of the ventricles and the amount of cerebrospinal fluid in the brain can give clues about an arachnoid cyst. If there’s a lot of fluid, the baby might also be diagnosed with hydrocephalus.

ultrasound image fetal development
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3. What Causes Choroid Plexus Cysts?

Choroid plexus cysts form when fluid becomes trapped within the layers of cells in the choroid plexus. 

Multiple cysts, resembling blisters beneath the skin, may form and are initiated around 6 weeks of gestation. The cysts become detectable via ultrasound scan around the 25th week of pregnancy. Despite not fully comprehending the reasons behind their occurrence, researchers have identified this cystic phenomenon.

Prenatal Checkup Ultrasound Session
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4. Choroid Plexus Complications

While the choroid plexus cysts may raise concerns, it’s crucial to note that their presence in isolation does not impact a person’s intelligence or cognitive development. 

Found in an area of the brain unrelated to thinking or reasoning, the choroid plexus has no bearing on overall health or intellectual abilities. In the absence of additional developmental issues, scientists consider a choroid plexus cyst a normal variant, assuring that it does not lead to any health disorders or disabilities.

Choroid plexus cyst (Medical Condition)

5. Choroid Plexus Cyst Risks

Choroid plexus cysts are usually not harmful and go away on their own over time. But sometimes, doctors worry about a rare genetic condition called trisomy 18 when they find a choroid plexus cyst in a baby. 

Trisomy 18 happens when a baby has an extra copy of chromosome number 18; sadly, most babies with trisomy 18 are stillborn, and those who are born often face serious problems and may not live for long.

Babies with this chromosomal abnormality can have difficulties with their thinking abilities and issues with organs like the heart, kidneys, and brain. 

About one-third of babies with trisomy 18 also have a choroid plexus cyst, and that’s why doctors want to take a closer look at these cysts. Another scan and diagnostic testing help them see the cysts better and find any other problems or chromosomal abnormalities.

newborn hospital care unit
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It’s important to know that trisomy 18 is very rare, happening in only 1 in every 3,000 newborns. Most babies with a choroid plexus cyst don’t have trisomy 18 and doctors usually find other issues along with the cyst in cases where a baby does have trisomy 18. If these problems aren’t seen in a second ultrasound, it’s unlikely that the baby has trisomy 18.

6. Detection of Choroid Plexus Cysts

Unfortunately, there isn’t a specific treatment for fetal choroid plexus cysts. Suppose you’re worried that your unborn baby might have trisomy 18. In that case, you can talk to your doctor or take genetic counseling about tests like the alpha-fetoprotein (AFP) test, which checks for possible DNA issues and genetic conditions. 

Another prenatal diagnosis called amniocentesis involves removing amniotic fluid from the uterus with a needle, where the liquid is then tested for signs of genetic problems that could affect your baby’s health.

However, amniocentesis comes with some potential risks, including:

  1. A leak of amniotic fluid through the vagina.
  2. A risk of miscarriage.
  3. During the procedure, the baby may get injured if they move their arms or legs.
  4. The baby’s blood cells may enter the mother’s bloodstream.
  5. Uterine infection and the chance of transmitting an infection from the mother to the baby.
Amniocentesis Concept Sticky Note Stethoscope
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Expectant mothers need to consider these risks when deciding whether to have amniocentesis. Even if the choroid plexus cyst disappears, there’s still a chance the baby could have trisomy 18. Choroid plexus cysts typically go away on their own in infants, even if there is a chromosomal issue.

The AFP test, which looks at protein levels in the mother’s blood, can also help rule out the possibility of the baby having trisomy 18. 

The amount of AFP found can also assist doctors in identifying other potential issues, such as Down syndrome, miscalculations in the due date, the possibility of twins, abdominal wall birth defects, chromosomal abnormalities, and open neural tube defects like spina bifida and anencephaly.

7. Alpha-Fetoprotein (AFP) Test

The AFP test is usually done between the 15th and 20th week of pregnancy and takes about one to two weeks to get the results.

Unlike amniocentesis, there are no extra risks associated with this test, and doctors may suggest the AFP test if they think there’s a higher chance of your unborn baby having a congenital disorder. If the combination of a level II sonogram and the AFP test doesn’t ease your concerns, amniocentesis can provide more information about your baby’s health before birth.

Alfa Feto Protein Test Stethoscope Top View
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It is a very rare condition, so there is not too much to stress about. However, if any complications are seen in early pregnancy, consult for any possible solution to prevent any mishaps. 

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