All of the following structures can be viewed through a bronchoscope, EXCEPT:

Subcarinal lymph nodes are mediastinal lymph nodes located around the carina on the other side of the tracheal wall and hence not visualized on bronchoscopy. Involvement of subcarinal nodes may be suspected on bronchoscopy by widening and fixity of the carina and/or paralysis of the vocal cords but these nodes cannot be 'directly visualized'.