Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Since earlier same day chest radiograph , there is near complete opacification of the left lung , likely due to new atelectasis from known obstructing left mainstem bronchial mass . The right lung appears to have mild pulmonary vascular congestion but no pulmonary edema . Heart size is difficult to assess . No pneumothorax . Right rib lesion is unchanged since prior exam and better assessed on reference CT chest .
    OUTPUT:
    
1 . Near complete opacification of the left lung , likely due to new atelectasis of the left lung from known obstructing left mainstem bronchial mass .