Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: PA and lateral radiographs of the chest demonstrate a small heterogeneous opacity in the left lower lobe and there is slight blunting of the posterior left costophrenic angle . The lungs are otherwise clear . The hilar cardiomediastinal contours are normal . There is no pneumothorax . Pulmonary vascularity is normal .
    OUTPUT:
    
Left lower lobe opacity and mild blunting of the posterior left costophrenic angle may represent atelectasis but pneumonia is also in the differential in the appropriate clinical setting .