Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Increased opacity overlying lower thoracic spine on lateral view likely corresponds to a site of subtle retrocardiac opacification on the PA view . The lungs are otherwise clear . Heart size is normal . The mediastinal and hilar contours are normal . The pulmonary vasculature is normal . No pleural effusion or pneumothorax is seen . There are no acute osseous abnormalities .
    OUTPUT:
    
Subtle retrocardiac opacification likely representing an early developing left lower lobe pneumonia .