Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart is at the upper limits of normal size . The aortic arch is calcified with slight unfolding . The mediastinal and hilar contours appear unchanged . There is no pleural effusion or pneumothorax . Streaky retrocardiac opacities are visible in the left lower lobe , more dense and crowded than on the prior study . Elsewhere , the lungs appear clear . Bony structures are unremarkable .
    OUTPUT:
    
Extensive but a streaky opacity in the left lower lobe , more dense than on the prior study but fairly similar in morphology . Accordingly , the possibility of chronic atelectasis or scarring could be considered , but a recurrent or superimposed infectious process is not excluded .