Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: PA and lateral images of the chest demonstrate a retrocardiac opacity that is consistent with a lower lobe pneumonia . This opacity is not seen on frontal exam , so it is unclear which side the pneumonia is on . Cardiomegaly is again noted . There is no pneumothorax or pleural effusion .
    OUTPUT:
    
Retrocardiac opacity concerning for lower lobe pneumonia .