Swelling on baby’s brain

We had our anatomy scan last Wednesday and the doctor said that the baby has some swelling on a ventricle on his left side of his brain. We have to go back in 4 weeks to see if the swelling went down. The doctor said this is nothing to worry about and he isn’t concerned but I’m obviously freaking out after he told me that. I was wondering if anyone has experienced this or knows if this could be a problem for the baby. Thanks in advance for any help.