I have enlarged vents also.
13 years after being shunted my latest MRI shows my vents slightly larger.
I have had a headache each and every minute of every day of the past 13 years.
As to the vents going back to a normal size that is one thing I have never heard would ever, ever happen.
Besides the neurosurgeons warn against trying to shrink the ventricle because that can cause a brain hemorrhage. The brain can pull away from the skull.
They all tell me that's a bad thing.