What Does Sonogram Showing Growth During 18 Weeks Of Pregnancy Indicate?

My sons wife is about 18 weeks pregnant. She had a routine sonogram today and we re told that there is a growth or shadow on the brain. They will be doing an aminosenticis tomorrow and will have a fetal brain scan is being scheduled for next week. I have read on other blogs that if it is a cyst, it may be nothing to worry about.