Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Cardiomediastinal contours are normal . There is a small area of increased opacity in the retrocardiac region . Is unclear if this represents an area of volume loss or small infiltrate The lungs are clear . There is no pneumothorax or pleural effusion . The osseous structures are unremarkable
    OUTPUT:
    
Small retrocardiac opacity . Unclear if this is volume loss or infiltrate . If old films become available would be happy dictate an addendum regarding interval change