Ahhh mama, I understand your worry, brain cysts can sound scary but from what I've heard from a few mum friends, small ones detected at 20-week scan sering hilang on their own as baby grows, especially yang kecil je macam yang doctor kata yours. The best thing is to follow up closely dengan your doctor at the next scan, they'll monitor it and give you better picture as pregnancy progresses, jadi don't stress yourself too much sekarang lagi. Sending you calm vibes, okay?