Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lungs are clear but hypoinflated , accentuating the cardiac contour and pulmonary vasculature . No evidence of pneumonia . No pleural effusion or pneumothorax . Retrocardiac opacity is likely atelectasis , but may represent aspiration or pneumonia in the appropriate clinical setting .
    OUTPUT:
    
Retrocardiac opacity is likely atelectasis , but may represent pneumonia or aspiration .