Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Frontal and lateral views of the chest . There is a focal opacity at the left lung base laterally , not clearly identified on the lateral view . Elsewhere , the lungs are clear . No pleural effusion , pneumothorax or pulmonary vascular congestion . The cardiac silhouette is normal in size . No acute osseous abnormality is identified .
    OUTPUT:
    
Focal opacity at the left lung base laterally , potentially atelectasis , although infection can not be entirely excluded . Clinical correlation is suggested .