Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The cardiac , mediastinal and hilar contours appear stable . The patient is apparently status post coronary artery bypass graft surgery . There is no pleural effusion or pneumothorax . There is a mild increase in patchy opacity in the left lower lobe which suggests minor atelectasis . Elsewhere the lungs appear clear . Deformity of the left anterior lateral left fifth rib appears unchanged .
    OUTPUT:
    
Mild increase in opacity at the left lung base suggesting mild increase in pre-existing atelectasis ; no definite evidence of disease .