Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Lung volumes are low . There is an opacity in the left lower lobe , obscuring the left hemidiaphragmic contour , likely a left pleural effusion . The upper lobes are clear . The cardiomediastinal contours are unchanged . There is atherosclerosis of the thoracic aorta . Spinal fusion hardware is unchanged in appearance . There is no pneumothorax .
    OUTPUT:
    
Left pleural effusion . Pneumonia can not be excluded .