Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart size is normal . The hilar and mediastinal contours are normal . In the retrocardiac region , subtle interval increase in density compared to the prior exam is likely positional . There is mild bibasilar atelectasis . There is no large pleural effusion , pneumothorax . The visualized osseous structures are unremarkable .
    OUTPUT:
    
Subtle interval increase in density in the retrocardiac region is likely positional , and less likely secondary to a focal consolidation .