Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Heart size is upper limits of normal . The mediastinal and hilar contours are normal . The pulmonary vasculature is normal . Lungs are clear except for a new patchy opacity in the left retrocardiac region . No pleural effusion or pneumothorax is seen . There are no acute osseous abnormalities .
    OUTPUT:
    
New patchy left retrocardiac opacity , which could reflect atelectasis , aspiration , or an early focus of infectious pneumonia .