A choroid plexus ultrasound is a specialized medical imaging procedure designed to visualize specific structures within the developing brain, typically performed during pregnancy. This non-invasive scan uses sound waves to create images of the choroid plexus, a network of tissue located in the brain’s fluid-filled cavities. The examination is most commonly incorporated into the routine second-trimester fetal anatomy survey, allowing practitioners to assess the formation and appearance of the brain structures.
What the Choroid Plexus Does
The choroid plexus is a delicate network of vascular tissue that resides within the ventricles, which are the interconnected, fluid-filled spaces inside the brain. Its primary function is the continuous production of cerebrospinal fluid (CSF), a clear substance that surrounds the brain and spinal cord. This fluid acts as a protective cushion, absorbing shocks and impacts that might otherwise damage the central nervous system.
CSF is responsible for transporting nutrients, hormones, and white blood cells while simultaneously removing metabolic waste products. The choroid plexus tissue also helps form the blood-cerebrospinal fluid barrier, which carefully regulates the passage of substances between the blood and the brain’s internal environment. The proper formation and function of this tissue are crucial for the healthy development of the entire nervous system.
Performing the Ultrasound
The choroid plexus is usually examined as part of the fetal anatomy scan performed around the 18th to 22nd week. During this prenatal scan, the sonographer uses a transducer placed on the mother’s abdomen, directing high-frequency sound waves through the uterus to capture cross-sectional images of the fetal brain. This timing is ideal because the fetal skull bones are not yet fully hardened, which allows sound waves to pass easily and visualize the internal structures.
In some cases, the scan may be performed postnatally on a newborn, particularly if there are concerns about neurological development or if the structure was not clearly seen prenatally. This neonatal procedure uses the infant’s fontanelles, or soft spots, as natural acoustic windows to obtain clear images of the brain’s ventricles and choroid plexus. The ultrasound procedure is painless and carries no known risks to either the mother or the fetus.
Understanding Choroid Plexus Cysts
The most frequent finding during a choroid plexus ultrasound is the presence of choroid plexus cysts (CPCs), which appear as fluid-filled sacs within the tissue. These cysts are relatively common, detected in approximately one to two percent of all pregnancies during the second trimester screening. CPCs are not considered a structural abnormality of the brain itself but rather a temporary variation in development.
The formation of a CPC is thought to occur when tiny amounts of cerebrospinal fluid become trapped within the delicate folds of the choroid plexus tissue. They can be found in one or both sides of the brain and may range in size from a few millimeters up to a centimeter. Importantly, when these cysts are found as an isolated feature, they are considered benign and do not affect the baby’s intelligence or cognitive function.
The majority of choroid plexus cysts are transient, meaning they resolve or disappear completely before the end of the second trimester. The cysts typically vanish as the brain continues its rapid development and the fluid is naturally reabsorbed, often by the 28th to 32nd week of gestation.
Interpreting Results and Next Steps
The interpretation of the ultrasound results centers on whether the choroid plexus cyst is an isolated finding or if it appears alongside other structural variations. When a CPC is the only finding on a comprehensive ultrasound, the risk of an underlying genetic condition is considered very low. In these isolated cases, no further action is typically recommended, and the pregnancy proceeds with standard care.
The concern arises when a choroid plexus cyst is found in combination with other anomalies identified on the same scan. This non-isolated finding may suggest an increased risk for a chromosomal condition, most notably Trisomy 18. While CPCs are present in a significant percentage of fetuses with Trisomy 18, the vast majority of fetuses with an isolated CPC do not have this condition.
If the ultrasound reveals a CPC along with other markers, such as heart defects, clenched hands, or growth restriction, the medical team will offer genetic counseling and further diagnostic testing. This may involve non-invasive prenatal screening (NIPS) or an amniocentesis, which provides a definitive diagnosis by analyzing the fetal chromosomes.