Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart is of normal size with normal cardiomediastinal contours . Increased retrocardiac opacity is most compatible with atelectasis . No diffuse pulmonary abnormality . No pleural effusion or pneumothorax . Osseous structures are unremarkable . No radiopaque foreign body .
    OUTPUT:
    
Increased retrocardiac opacity , compatible with atelectasis . No pneumothorax or pneumomediastinum .