I'm so sorry you are going through this. I have no experience with this, but I would do some research like you have been, take alist of questions and ask your doctor everything on your list and not leave until you have answers. Frow what I understand, if the rest of the baby's ultrasound is healthy, then the cyst shouldn't be too harmful. Here is some research I found, though I don't know how credintialed it is.
here is a good link with some resources as well:
"Your doctor probably saw a "choroid plexus cyst" (CPC) inside the fetus' head. Be reassured that if the CPC is a single small cyst and no other problems are found with the fetus, chances are good that the baby is going to be OK.
The choroid plexus is soft tissue in the ventricles, which are fluid-filled spaces located on both sides at the base of the brain. The choroid plexus itself is in the head but not in the brain per se, but it contains fluid that bathes the spinal cord (via the ventricles) and the brain itself.
Cysts are pockets of fluid and/or cells. During an ultrasound, a technician will check the choroid plexus for any dark spots, which may indicate fluid or a cyst. In the second trimester, any spot in the choroid that's bigger than 10 millimeters is considered a cyst worth mentioning. CPCs, which occur in as many as one in 40 normal pregnancies, are small cystic areas often found on routine second-trimester ultrasounds. Half the time, CPCs occur on one side of the brain only (unilateral), and the other half they're on both sides (bilateral). Well over 90% of CPCs disappear on their own by the 26th week of pregnancy without ever affecting the fetus.
Although there's some controversy over whether fetuses with CPCs have an increased risk of chromosome abnormalities, if there is a risk, it's very small. If a fetus has only one isolated cyst smaller than 10 mm, the risk is probably no more than it would be anyway based on the mother's age. But if the fetus has other abnormalities, the risk rises. That's why it's important to do a thorough ultrasound exam and check for chromosomal anomalies. In most fetuses with trisomy 18 (Edwards syndrome), for example, and many with trisomy 21 (Down syndrome), signs of the abnormalities show up on ultrasound."
A complete ultrasound provides information that will help you, your partner, and your doctor decide whether you need an amniocentesis, the ultimate diagnostic tool for chromosomal anomalies. Usually, in the case of CPCs, parents must weigh the risk of having an invasive procedure such as an amniocentesis against their desire to make sure the fetus has no chromosomal anomalies.