Mass on back of baby head(help)

Kemyra
I just want an idea of the problem and what I can maybe do to help. At today's ultrasound i was told one of my twins has a mass or cyst or pocket of fluid or SOMETHING on the back of its head. Do any of yAll have an idea of what it could be or any way I could help. Anything is helpful I just need information. I'm going for genetic testing soon