Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Heart size is normal . The mediastinal and hilar contours are unremarkable . The pulmonary vasculature is not engorged . Retrocardiac opacity is concerning for infection . No pleural effusion or pneumothorax is clearly present . There are no acute osseous abnormalities .
    OUTPUT:
    
Retrocardiac opacity is concerning for infection .