Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Heart size is normal . Cardiomediastinal silhouette and hilar contours are unremarkable . There is linear atelectasis as well as a subtle opacity in the left lung base . The lungs are otherwise clear . Pleural surfaces are clear without effusion or pneumothorax .
    OUTPUT:
    
Subtle left base opacity concerning for pneumonia .