Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lung volumes are low . There is ill - defined opacity in the left lung base , mildly silhouetting out the left cardiac border . The right lung is unremarkable . There is no pneumothorax or pleural effusion . The median sternotomy wires are intact . There is evidence of prior CABG with clips at the mediastinum . A mildly calcified aortic knot is again noted .
    OUTPUT:
    
Ill - defined left basilar opacity , could be atelectasis or infectious process .