Hilar prominence

Hi, I have been having a burning pain in the upper left of my chest for the past 3 months which only occurs approx 1 hour after rising in the morning & comes and goes for about 30 minutes and then I have no more discomfort till the next morning. It varies in intensity and the pain can travel down my left arm. I had an Xray and was called back a week later for another Xray from a differant angle to investigate left hilar prominence I am aged 58 and considered myself to be in good health, I am also a non smoker. I am still waiting for the results but am curious as to what hilar prominence actually describes. Alec