Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Compared to prior , the lung volumes have increased . Right lower lobe atelectasis has since resolved . However , there is residual retrocardiac opacity . There is no pleural effusion or pneumothorax . The cardiomediastinal silhouette and hilar contours are unchanged from prior . Opacity in the left mid lung with surgical clips in place is compatible with prior RFA site . Subcutaneous emphysema has improved .
    OUTPUT:
    
Residual retrocardiac opacity , possibly atelectasis , though can not exclude pneumonia .