Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart is normal in size . The mediastinal and hilar contours appear within normal limits . There is retrocardiac opacity , probably referring to opacity in the left lower lobe , although best seen on the PA view , suggesting pneumonia . The lungs appear otherwise clear . There is no pleural effusion or pneumothorax .
    OUTPUT:
    
Findings suggest pneumonia in the left lower lobe .