Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: A linear opacity at the left base is most likely atelectasis and / or scarring . It is similar to the prior CT . Subtle left midlung / perihilar opacity is also seen . There is no overt pulmonary edema . Blunting of the left costophrenic angle is likely due to a small left pleural effusion . There is no large right pleural effusion . There is no pneumothorax . The cardiomediastinal silhouette is normal .
    OUTPUT:
    
Small left pleural effusion . Left mid lung opacity may be atelectasis although infection is also possible .