My ventricles were "mildly" enlarged when I was diagnosed...however, because of double vision and incontinence issues, my NSG felt I had high pressure, and so the shunt.
I've had lots of CT scans since the initial shunt and revisions. Diagnosed 2006. My ventricles have always been read as "stable, no change since preoperative CT scan." When I've questioned my NSG about this, he explained that it was important to keep on top of the pressure problems, and he didn't want to drain too much. Haven't had too many problems lately, so I am more comfortable with the ventricle sizes not being any smaller. I am seeing NSG every three months, plus opthalmologist, neurologist, to stay on top of things. And I understand about the importance of not overdraining the ventricles, so feel okay about it.
That's just my story. I know they can get a measurement on the size of the ventricles to see if there is any change either way. Pressure was the main problem with mine. I may have had the hydro for some time without symptoms.
Good luck!