Hi there -
It is probably not a reason for conern, but probably should be followed up on a routine basis for a while to be certain it doesn't change. Most of these wind up being calcified old lesions from some lung damage due to infection or aspiration of something in the past. Sometimes they aren't even that, just some random artifact.
It would be prudent of your doctor to repeat the chest x-ray at six months or a year, but if that shows no change then it can be safely disregarded.
Best of luck to you.
John Kenyon, EMT, CCT
Non-invasive cardiology tech, Emergency and Critical Care technician, Critical Incident Stress Mgmt. specialist