What does "subtle increased attenuation in the rightperihilar region" relative to a chest x-ray mean?

Shade o'Gray. Use...: HT Prime. The perihilar region is the part of the lung where the airways & arteries enter. "Increased attenuation" means that the picture (actually, the negative) is brighter. That could be from the presence of inflammatory fluid or infection or congestion, but most often means that the Radiologist ought to check his glasses or equipment. Without symptoms, it's a meaningless (but costly) finding.