Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart size is normal . The mediastinal contours demonstrate no widening . The previously described pneumomediastinum is subtly present along the left aspect of the trachea , but better appreciated on prior exam . The lungs are clear . There is no pneumothorax or pleural effusion .
    OUTPUT:
    
Pneumomediastinum better appreciated on prior CT , but no pneumothorax .