No answer yet. Most info I've found on "mass effect" has to do with growth in the brain. I did end up finding a couple of sites that point to lung cancer when the "mass effect" is on the subclavian artery. I'm hoping that the MRA rules out any kind of mass! I'm assuming that it's usually a benign or malignant tumor, possibly cyst growth, that effects the nerves, arteries, etc. I'm hoping to hear from someone that has had a "mass effect" so that I am aware of the possibilities it presents. Does it need to be removed, is it invasive, does it matter if it's benign or not when effecting an artery, etc?

Thanks for responding. Are you curious as well? Any kind of similar situation?