Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lungs are clear . The cardiac , hilar and mediastinal contours are normal aside from a slightly prominent aortic knob , which may be a normal variant . No pleural abnormality is seen . No rib fractures are seen .
    OUTPUT:
    
No acute cardiopulmonary process . Slightly prominent aortic knob may be a normal variant , however clinical consideration should be given to the possibility of an acute aortic syndrome .