Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The patient is status post median sternotomy and CABG . Heart size remains normal . Mediastinal and hilar contours are unchanged . The pulmonary vascularity is normal . Elevation left hemidiaphragm is stable . Retrocardiac opacity is nonspecific and could reflect atelectasis , pneumonia or aspiration . No large pleural effusion or pneumothorax is identified . There are mild degenerative changes in the thoracic spine .
    OUTPUT:
    
Elevated left hemidiaphragm with adjacent retrocardiac opacity likely reflecting atelectasis though infection or aspiration can not be excluded .