Choroid plexus cysts are small cystic areas in the choroid plexus. The choroid plexus is spongy tissue in the ventricle of the brain. It is not in the substance of the brain itself. These cysts are:
Very common. With better ultrasound equipment they keep getting more common.
Not in the brain per se, but in the choroid, the tissue in the ventricle that makes spinal fluid.
Will almost always go away by 24 weeks or so, and *never* damage the brain.
*May* have a slight increased risk (1-1.5% chance) that the baby has trisomy 18 or trisomy 21. There is controversy on this point, but almost all agree that if the cysts are not greater than 10 mm or bilateral, there is probably no increased risk over that of the mother's age.
If the baby opened its hand during the ultrasound, the chances of trisomy 18 may be markedly decreased. If there were no other abnormalities seen, the chances are low also.
Now, having said that the risk is probably very low, if the baby does have trisomy 18, it is a severe and fatal chromosome disorder, with most babies dying shortly after birth. However, most trisomy 18 babies will have other abnormalities seen on ultrasound and will not open their hands. So the decision to have amniocentesis may depend on the mother's age, the adequacy of the ultrasound for other abnormalities, the size and location of the cysts, and the particular burden that a possility of trisomy 18 implies compared to the risk of miscarriage from the amniocentesis.
