Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Lung volumes are low . There is a mildly increased retrocardiac opacity likely representing atelectasis . The heart remains moderately enlarged . The thoracic aorta appears tortuous . There is no pleural effusion or pneumothorax . No acute fractures are identified .
    OUTPUT:
    
Mildly increased retrocardiac opacity likely representing atelectasis ; however , a superimposed pneumonia must be excluded in he proper clinical setting .