Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The previously visualized 4 mm right apical pneumothorax has not changed since ___ . Small left pleural effusion has improved since the prior CXR . Right lung is essentially clear . There is persistent post-operative pneumomediastinum . Stable moderate cardiomegaly . Patient is status post mechanical aortic valve replacement .
    OUTPUT:
    
1 . Millimetric right apical pneumothorax has remained stable . 2 . Small left pleural effusion has improved . 3 . Mild pneumomediastinum , an expected post-operative finding .