Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: A tracheostomy tube terminates 3 .7 cm above the carina . Lung volumes are slightly diminished , resulting in crowding of the bronchovascular structures . Opacity at the left lung base could reflect pneumonia or atelectasis . No pleural effusion or pneumothorax . Heart is normal size . The appearance of the mediastinum is stable , with unfolded aorta . An old healed right clavicular fracture is noted .
    OUTPUT:
    
Opacity at the left lung base , which may reflect atelectasis or pneumonia .