Bad news at my ultrasound appointment

At my ultrasound appointment today, I was told a part of my baby's brain is .3 cm bigger than what it should be which is 1 cm not 1.03 cm which is what my baby is measuring at. I have a follow up appointment in 4 weeks. I was too emotional to ask any questions. Does anyone have any information? All I know is that this part of the brain releases fluid to the spinal cord, And shouldn't be bigger than 1 cm. I know this is super vague and I have emailed my doctor for more information and I'm thinking maybe someone on here will be able to share similar experiences. Thank you.