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 no pleural effusion or pneumothorax . Retrocardiac opacity is consistent with patchy focal opacification of the left lower lobe . Elsewhere , the lungs appear clear .
    OUTPUT:
    
Patchy left lower lobe opacity . Although pneumonia or aspiration could be considered , findings could be seen with atelectasis . Correlation with clinical circumstances and short - term follow - up radiographs may be helpful .