Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Upright portable radiograph of the chest demonstrates a small left apical pneumothorax , which is stable in comparison to the prior study with no evidence of increased shift of the mediastinal structures . The right lung is unchanged . The heart size is also stable .
    OUTPUT:
    
Small left apical pneumothorax is stable in size . Otherwise , no change since the prior study .