Choroid Plexus Cysts
What are Choroid Plexus cysts?
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 these chambers communicate
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 babies brain (figure 1). Fluid leaves the 4th chamber
and circulates about the brain thus providing the brain with
a protective layer of fluid, which buffers it against insult
or injury.
The chambers in the centre of each hemisphere are lined
with by 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).
How common are they?
Choroid plexus cysts are a variation of normal and 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. For
this reason they are considered as an ultrasound "phenomena"
i.e. they are only seen on ultrasound at a particular time
in pregnancy (14-24 weeks) and then disappear.
Should I be concerned if my baby
has Choroid Plexus Cysts?
While they are a common finding in normal pregnancies, they
are also seen in fetuses with chromosomal abnormalities such
as Edward's syndrome (see below). But in the vast majority
of babies who have Edwards syndrome there are many abnormalities
in addition to CPC's. In fact over 99% of babies with Edwards
syndrome have other abnormalities most of which can be identified
with ultrasound. So once a CPC is identified, a careful examination
to determine if these abnormalities are present will be performed.
If no such abnormalities are present in your baby, you will
be reassured. Your level of reassurance will be provided as
a risk estimate i.e. the chance of you having a baby with
Edwards syndrome where an CPC is identified and the scan is
otherwise normal. This figure is usually well below 1in 300.
This information will be provided on the ultrasound report
and will be discussed further with your Doctor.
If you remain concerned about the level of reassurance provided
or remain in general concerned about matters you may want
to proceed with a definitive genetic test such as amniocentesis.
This directly tests the baby's chromosomes and gives a definitive
answer rather than a level of reassurance, as provided with
ultrasound. It is a test however that carries a small risk
of miscarriage (0.5%, Refer to the amniocentesis booklet).
With ultrasound however most patients are given a very low
risk i.e. 1in 1000 or less and choose not to proceed with
amniocentesis.
What is Edwards syndrome?
A normal baby has 23 pairs of chromosomes in every cell of
its body, i.e. a total of 46 chromosomes. Edward syndrome
is where the baby has an extra copy of chromosome number 18,
i.e. a total of 47 chromosomes. This gives rise to both multiple
severe physical and mental deformities, which in the vast
majority of cases is not compatible with life. In fact the
majority of pregnancies with this chromosome problem result
in miscarrige. Some however survive further into the pregnancy
and result in late unexpected fetal demise or stillbirth (death
shortly after delivery). Only very rarely however do babies
with this severe abnormality survive after birth. The physical
deformities with Edward syndrome include congenital heart
abnormalities, spina bifida, brain abnormalities, abdominal
wall and liver abnormalities, limb abnormalities, kidney abnormalities
etc.
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