Like you, I had a routine ultrasound that showed a choroid plexus cyst on my son's brain at 20 weeks. Of course, I completely freaked out and was distraught. I did more research and found that 99.5% of the time, it's nothing to worry about. In fact, my OB said that it's something they're reluctant to tell parents about because it is almost always harmless but causes more worry than anything else. Suffice it to say, my son is now 2 1/2 y.o., and IMHO, none the worse for wear. He knows all his letters, letter sounds, numbers, colors, shapes (inclu. rhombus, pentagon, hexagon, etc.), days of the week, etc. He's starting to read CVC words. So, no... it did not cause any brain damage or other averse effects. So don't spend your days worrying (easier said than done!) because your AFP risk levels are low. Chances are incredibly high that it will simply go away on its own. Best wishes!