Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: As compared to chest radiograph from 1 day prior , near complete opacification of the left lung from a combination of pleural effusion and left lung collapse . There is abrupt cut off of the left main bronchus . Minimal aeration of the left upper lobe . Small right - sided effusion .
    OUTPUT:
    
Near complete opacification of the left lung from a combination of substantial increase in the pleural effusion and further left lung collapse . The large pleural effusion is of unclear etiology .