Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lungs are normally expanded . Retrocardiac opacity best seen on the lateral projection on the study ___ is not definitely seen on this single frontal projection . Heart size is normal . The mediastinal and hilar contours are normal . There is no pleural effusion or pneumothorax .
    OUTPUT:
    
No acute cardiopulmonary abnormality . Retrocardiac opacity seen on the lateral radiograph on the prior study is not definitely appreciated on this single projection . If clinically indicated a lateral radiograph could be obtained for comparison .