Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is a left lower lobe retrocardiac opacity , more pronounced from ___ , which is concerning for developing pneumonia rather than atelectasis superimposed on a pre-existing lesion as seen on the prior PET - CT . A subtle right apical opacity is again seen and may relate to apical pleural thickening . The lungs continue to be hyperinflated , likely representing chronic obstructive pulmonary disease . There is no pleural effusion or pneumothorax . The heart and mediastinal contours are within normal limits .
    OUTPUT:
    
Increased left lower lobe retrocardiac opacity is concerning for developing pneumonia rather than atelectasis superimposed on a pre-existing lesion as seen on the prior PET - CT .