Shunts do drain water from the vents. The shunt is placed on the side of the head with the entension that drains the fluid form the vents going into the ventricle. My guess as to the size of your vents not changing is that you have slit ventricls; or overdraining, that can happen when someone has been shunted long term. I've been shunted for all 35 years of my life and have severe slit vents. I had an anti-syphen devise put in on April 15, that has helped, but is not perfect. My doctor does not want to lower the pressure of my programmable shunt because he's afraid my ventricls would collapse. I don't know what happens if that happens, but it can't be good.
You have to see a NEUROSURGEON for your shunt, not a neurologist. Neurologis don't know the first things about shunts and just push medication down your throught. I would not trust them if their tounnge came notorized. Long story made short, I went to one because I jerked, and he put me on Cojentin that made me severly confused. I dithched that medication and figured out it was Cymbalta. I had one that put me on some pain medication so powerful I slept all the time. Now I refuse to go to one. They are all ding bats.