Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There is a retrocardiac opacity which persists on the lateral view . Elsewhere , lungs are clear . The cardiomediastinal silhouette is stable . No acute osseous abnormalities .
    OUTPUT:
    
Vague increased retrocardiac opacity which could represent left lower lobe pneumonia . Please note this finding was similar when compared to prior and followup will be necessary to ensure resolution .