Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Compared to prior , the lung volumes are low . Left retrocardiac opacity likely reflects increased left lower lobe opacity , concerning for pneumonia . The heart size is mildly enlarged . The mediastinal and hilar contours are unchanged . Aortic knob calcification is unchanged . Abdominal drainage tube is again seen .
    OUTPUT:
    
Possible left lower lobe pneumonia or atelectasis