Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The left mainstem bronchus is not definitively visualize ; however , there is no no increased left lung opacification to suggest obstruction . Minimal bibasilar atelectasis is identified . Cardiomediastinal contour is normal . No pleural effusion or pneumothorax identified .
    OUTPUT:
    
Nonvisualization of the left mainstem bronchus without focal lung opacification .