Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: PA and lateral views of the chest demonstrate a persistent small apical pneumothorax on the left , not significantly changed since the prior study . No pneumothorax is identified on the right . There is mild left basilar atelectasis . The cardiomediastinal silhouette is unremarkable , and there is no evidence of tension . No displaced rib fractures are identified . There is no pleural effusion or focal airspace opacity .
    OUTPUT:
    
Small left apical pneumothorax .