Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The patient is status post median sternotomy . The heart size is normal . The aortic knob is calcified . The mediastinal and hilar contours are otherwise unremarkable . There is no pulmonary edema , pleural effusion or pneumothorax . Streaky retrocardiac opacity could reflect atelectasis but infection is not excluded . There are no acute osseous abnormalities . No subdiaphragmatic free air is seen .
    OUTPUT:
    
Streaky retrocardiac opacity may reflect atelectasis but infection is not excluded . No subdiaphragmatic free air .