I googled and found this. Looks like it is very normal. And I am pretty sure I remember hearing about this on a show one time about fetal development. Since you said everything else on the baby was totally normal and fine, I would not worry.
Choroid plexus cysts are just a collection of fluid in the part of the baby's brain that makes the fluid that cushions the brain and spinal cord. The "cyst" is just a small build-up of fluid as it moves through the connecting tubes. As the baby grows the tubes get bigger and the fluid moves on. CPC's are almost always gone by 24 weeks and do no harm to the baby's brain.
CPC's look like black spots in the hemispheres of the brain.
Babies with Edward's syndrome (Trisomy 18) are found to have CPC's. However research has shown that babies with Edward's syndrome also have other abnormalities, such as strawberry-shaped head (see image below), overlapping fingers and abnormal feet, heart, kidney or abdominal problems.
It is known that 1% of babies have one or more CPC's in early pregnancy (see image 2 below). In the absence of other markers (isolated CPC's) they are insignificant and Sonographers in many hospitals don't even mention them any more.