Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lung volumes are slightly decreased compared to the most recent prior radiograph . Left retrocardiac opacity most likely represents atelectasis . No new opacity concerning for infection . Moderate cardiomegaly persists . The mediastinal and hilar contours are normal . There are multiple gas - filled loops of bowel in the abdomen .
    OUTPUT:
    
Retrocardiac opacity could represent aspiration or infection in the correct clinical setting .