Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is retrocardiac opacity silhouetting the descending thoracic aorta with spine sign on lateral view compatible with a left lower lobe pneumonia . Lungs are otherwise clear . The cardiomediastinal silhouette is within normal limits . No acute osseous abnormalities .
    OUTPUT:
    
Left lower lobe pneumonia .