Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP upright and lateral chest radiograph demonstrate a retrocardiac opacity , best seen on the lateral image , for which an infectious process can not be excluded . Heart is borderline enlarged . No overt pulmonary edema is visualized . There is no pleural effusion or pneumothorax . Aortic arch calcifications are noted , similar in appearance to prior study dated ___ .
    OUTPUT:
    
Retrocardiac opacity best seen on the lateral view , for which an acute infectious process can not be excluded .