Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiomediastinal contours appear to be exaggerated due to low lung volumes . Subtle opacities at the left lung base are likely secondary to atelectasis . There is no large pleural effusion or pneumothorax . The visualized osseous structures are unremarkable .
    OUTPUT:
    
Subtle opacity at the left lateral lung base may be secondary to atelectasis ; however , an acute infectious process can not be excluded .