Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: A retrocardiac opacity in the left lower lobe could represent atelectasis , though aspiration or infection can not be fully excluded . Linear bibasilar opacities likely represent atelectasis . There is no evidence of pleural effusion , pulmonary edema or pneumothorax . The heart is mildly enlarged , and median sternotomy wires are seen .
    OUTPUT:
    
Left retrocardiac opacity could represent atelectasis , though aspiration or infection is not fully excluded .