Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The patient is status post coronary artery bypass graft surgery . Lines , tubes , and drains have been removed . The cardiac , mediastinal and hilar contours appear stable . Slight residual blunting of the left costophrenic angle suggests a very small effusion . In the basal left lower lobe , there is a focal opacity . Whether this may be residual improved atelectasis associated with fairly recent prior surgery or pneumonia is uncertain , but in general the lungs are much better aerated , including the left base .
    OUTPUT:
    
Left basilar opacity . This appearance could be due to improving left basilar opacification , although new pneumonia in the left lower lobe is not excluded .