Choroid Plexus Cysts
Choroid plexus cysts are a variation of normal and are seen in approximately 1-3% of normal pregnancies. They are NOT a brain abnormality and in all cases disappear with time. There is therefore little benefit in performing a scan in later pregnancy as they universally disappear with time.
The fetal brain is made up of 2 hemispheres separated by a thick band of tissue. Within each hemisphere there is a small chamber of fluid (the ventricles). Each of the chambers communicates via a narrow “pipe-like” channel to a central chamber (3rd ventricle) which in turn communicates with the 4th chamber at the back of the baby’s brain. Fluid leaves the 4th chamber and circulates about the brain thus providing the brain with a protective layer of fluid, which buffers it against injury.
The chambers in the centre of each hemisphere are lined with a thick layer of material called the choroid. The choroid produces the fluid, which circulates throughout the chamber system. The carpet like layer of material is spongy in appearance and composed of many fluid filled spaces of different sizes. Some of these fluid filled spaces or cysts are large and some small. With the advent of high resolution ultrasound machines it is now possible to see into the centre of the fetal brain and identify this tiny spongy layer. Where the fluid spaces are large and easily identified they are called ‘choroid plexus cysts’ (CPC’s).
CPC’s are a common finding in normal pregnancies. However they are also seen in fetuses with chromosomal abnormalities such as Edward’s syndrome. In the majority of fetuses with Edward’s syndrome there will be many abnormalities in addition to CPC’s. Once a CPC has been identified careful examination of the rest of your baby will be performed. If no further abnormalities are present in your baby you will be reassured and provided with a risk estimate of you having a baby with Edward's syndrome. This figure is usually much better than 1 in 300. This information will be provided to you and your doctor.
If you remain concerned about the risk estimate you may want to proceed with a definitive genetic test such as amniocentesis.