Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lung volume is small . A retrocardiac opacity obscuring the left hemidiaphragm is new compared to yesterday . This is most likely due to worsening atelectasis rather than pneumonia . The right lower lobe atelectasis has increased . The cardiac silhouette is enlarged but stable . The mediastinum is unchanged . No pleural abnormalities or pneumothorax .
    OUTPUT:
    
Retrocardiac opacification likely due to atelectasis rather than pneumonia .