Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: A thoracic aortic graft is in place . Accounting for differences in technique , the heart size is unchanged and normal . Retrocardiac opacity is noted sihouetting the descneding thoracic aorta . There is no pleural effusion or pneumothorax . There are no signs of pulmonary edema .
    OUTPUT:
    
Retrocardiac opacity may represent atelectasis or scarring though , pneumonia should be considered in the correct clinical setting .