Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP upright and lateral views of the chest were obtained . A chest tube is again noted at the right base . There is a persistent small right apical pneumothorax , not significantly changed compared to the prior examination . Lungs are clear . Cardiomediastinal silhouette is stable . There is no pleural effusion . Patient is status post mitral valve replacement .
    OUTPUT:
    
Stable small right apical pneumothorax .