Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Cardiac size is top normal . The aorta is slightly tortuous . A retrocardiac opacity likely represents atelectasis but underlying infection can not be excluded . There is no large pleural effusion . There is no pneumothorax . Surgical clips in the right upper quadrant .
    OUTPUT:
    
Retrocardiac opacity , likely atelectasis , but infection in the correct clinical setting should be considered .