Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Heart size is normal . Mediastinal and hilar contours are unremarkable . Pulmonary vasculature is not engorged . Patchy opacity is noted in the left lung base , which may reflect atelectasis but infection is not excluded . Right lung is clear . No focal consolidation , large pleural effusion or pneumothorax is present , though the right costophrenic angle is excluded from the field of view . Multiple old left - sided rib fractures are re - demonstrated .
    OUTPUT:
    
Patchy left basilar opacity may reflect atelectasis , but infection can not be excluded in the correct clinical setting .