Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is vague opacity in the retrocardiac region on the frontal view without correlate of opacity on the lateral view . There is no effusion or edema . The cardiomediastinal silhouette is within normal limits . No acute osseous abnormalities .
    OUTPUT:
    
Subtle retrocardiac opacity only seen on the frontal view likely atelectasis . No definite evidence of pneumonia .