Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Focal opacity seen over the posterior costophrenic angle localizing to the left on the frontal view . Elsewhere , the lungs are clear . Cardiac silhouette is top normal . No acute osseous abnormalities .
    OUTPUT:
    
Focal left basilar opacity which could be atelectasis although infection is possible in the proper clinical setting .