What might cause mri=mild lateral compression of midbrain? nothing else noted as far as masses etc, but image is slightly obstructed by va shunt artifact fitted for presumed aytipical-idiopthc ih. does comp cause symptoms?

Mass effect?: It sounds like the MRI noted certain abnormalities and that the shunt was slightly obstructing the view. Please ask your own physician about these results in your own case. You would get a more informed answer that way than from doctors who don't know you and haven't seen the image.

I doubt it's ..,,: Anything serious. The midbrain controls basic functions like heart rate, breathing, alertness, body temperature. I suspect it may be an old deviation related to your ih. But perhaps a possibility of increased pressure in your ventricles/shunt obstruction. Please check w your neurosurgeon if concerned or any symptoms.