Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Subtle patchy left base opacity may be due to atelectasis or subtle pneumonia . No pleural effusion or pneumothorax is seen . The cardiac and mediastinal silhouettes are unremarkable .
    OUTPUT:
    
Subtle patchy left base opacity best seen on the frontal view may be due to atelectasis or subtle pneumonia .