Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP upright and lateral views of the chest provided . An IVC filter is again seen at the cavoatrial junction . Previously noted PICC line has been removed . Subtle retrocardiac opacity may represent a very early pneumonia . Otherwise the lungs appear clear . Coarsened lung markings suggest underlying interstitial lung disease . No large effusion or pneumothorax . Heart size is normal . Mediastinal contours unremarkable . Bony structures are intact .
    OUTPUT:
    
Subtle opacity in the left lower lobe is concerning for pneumonia . Probable underlying interstitial lung disease .