Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP and lateral images of the chest . The lungs are well expanded . Bibasilar atelectasis is seen . There is a retrocardiac opacity , which may represent atelectasis but can not exclude pneumonia or aspiration in the right clinical setting . No large pleural effusion or pneumothorax is seen . The cardiomediastinal silhouette . The aorta is demonstrates chronic aneurysmal enlargement .
    OUTPUT:
    
Retrocardiac opacity , which may represent atelectasis but can not exclude pneumonia respiration the right clinical setting .