Chest X-Ray Interstitium Coarse?

[JD1255]

28/male/non smoker/Asthma/Allergies/GERD. I recently had a chest x-ray for chest tightness and shortness of breath. The x-ray came back normal except the doctor stated in his findings that my interstitium was slightly coarse for my age. What does that mean? I tried doing research about it and all I could find was information about Pulmonary Fibrosis and Hypersensitivity Pneumonia. I am starting to get a little concerned. Any information would be helpful.