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

Arachnoid vs. Choroid Plexus Cysts in the Fetal Brain

Pregnancy is a beautiful experience but on the same side, one needs to be very careful about it. I believe any pregnant lady should never miss routine checkups and ultrasounds etc. I am saying this because you never know what complication might come up. So, it’s better to treat it at the infant stage before the condition becomes serious. For example- cysts in the fatal brain. Here, I’ll tell you some important details about it.

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.

First I’ll Talk About 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 1-2% 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
Source: Depositphotos

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. 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.

Diagnosing Arachnoid Cysts
Source: Depositphotos

Do You Know 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.

Ultrasound scan
Source: Depositphotos

We interviewed Dr. Matthew Casavant, a physician and owner at South Lake OBGYN, and tried to understand the fetal brain cysts, particularly arachnoid and choroid plexus cysts. With his extensive experience in obstetrics and gynecology issues, he offered his valuable expertise. Here is what he said:

Dr. Matthew Casavant
Dr. Matthew Casavant

“Arachnoid and choroid plexus cysts in fetal brains are topics I encounter fairly often in my practice, especially given my focus on early fetal screenings and the use of ultrasound technology.

These types of cysts can indeed be detected during routine screenings, particularly during the second-trimester anatomy scan, usually conducted around 18-22 weeks of gestation.

The accuracy of ultrasound in diagnosing these cysts is generally high, but understand that most of these cysts, particularly choroid plexus cysts, are benign and typically resolve on their own without impacting the baby’s developmental outcomes.

In cases where these cysts are identified, the critical step is differentiating between benign findings and markers for more serious conditions, like trisomy 18.

This is where a detailed ultrasound examination and sometimes additional diagnostic tests come into play. For instance, the presence of isolated choroid plexus cysts with no other abnormal ultrasound findings might not indicate a significant risk for trisomy 18.

However, if these cysts are accompanied by other anatomical abnormalities, further testing such as non-invasive prenatal testing (NIPT) or more invasive procedures like amniocentesis may be recommended to evaluate the risk of chromosomal abnormalities accurately.

For expectant parents facing such findings, it’s critical to have open and informative discussions with your healthcare provider.

In my experience, providing comprehensive education around these issues and supporting patients through their decision-making process can significantly alleviate anxiety and empower parents as they navigate their pregnancy journey.”

The Choroid Plexus May Have Some 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 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.

Baby with trisomy 18
Source: Depositphotos

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.

In an interview with the Icy Whiz Team, Dr. Himali Maniar Patel, Gynecologist, MBBS, DGO, a Consultant at ClinicSpots, shares her perspective on fetal brain cysts. Here is what she said:

Dr. Himali Maniar Patel
Dr. Himali Maniar Patel

Understanding Fetal Brain Cysts

  • Arachnoid and Choroid Plexus Cysts

Arachnoid and choroid plexus cysts are fluid-filled sacs that can occur within the fetal brain during gestation. These cysts are generally considered benign and are often detected incidentally during routine prenatal ultrasounds. Most arachnoid and choroid plexus cysts do not interfere with brain development and typically resolve independently before birth.

  • Accuracy of Ultrasound in Diagnosing Fetal Brain Cysts

Prenatal ultrasounds offer a non-invasive method to visualize fetal brain structures.

High-resolution ultrasounds can accurately identify arachnoid and choroid plexus cysts.

The detection rate and accuracy can vary depending on the gestational age and the quality of the ultrasound equipment.

  • Implications for the Baby’s Health

Most fetal brain cysts, particularly isolated choroid plexus cysts, have no significant impact on the baby’s health. In rare instances, these cysts could be associated with chromosomal abnormalities, such as trisomy 18, but the presence of cysts alone without other markers has minimal risk.

  • Differentiating Between Benign Cysts and Chromosomal Abnormalities

The differentiation is based mainly on associated anomalies or markers suggestive of a chromosomal condition.

Comprehensive ultrasound examinations assess the entire fetus for additional anomalies that could indicate a chromosomal abnormality.

Non-invasive prenatal testing (NIPT) and invasive testing methods like amniocentesis can provide further clarification.

  • Considerations for Expectant Parents

Discussing the findings and implications with a fetal medicine specialist or genetic counselor is crucial.

Parents should consider the sensitivity, specificity, and risks associated with further diagnostic tests.

The management plan for fetal brain cysts often involves serial ultrasounds to monitor cyst size and resolution.

Management of Fetal Brain Cysts

  • The management approach typically includes:

Regular monitoring through ultrasounds to track the evolution of the cysts.

In cases where cysts are associated with other anomalies, further genetic testing may be recommended.

Counseling and providing emotional support for parents to help them understand the findings and implications.”

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.
Source: Depositphotos

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 tubes defects like spina bifida and anencephaly.

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.

Alpha Fetoprotein Test | Understanding AFP, Uses of Test, Results and Interpretation

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. Understanding the specific findings, the associated risks, and the options for further testing can help parents make informed decisions that align with their values and preferences.

Guest Author: Saket Kumar

Last Updated on May 20, 2024 by Pragya


Anushree Khandelwal

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