Direct bronchoscopy can visualize all except

Bronchoscopy: Looking through the scope, tip of epiglottis is identified first and the scope passed behind it and the epiglottis lifted forward to expose the glottis. Now bronchoscope is rotated 90deg clockwise so that its bevelled tip is in the axis of glottis to ease its entry into the trachea. Once trachea is entered, scope is rotated back to the original position. Bronchoscope is gradually advanced and the entire tracheobronchial tree examined. Axis of bronchoscope should be made to correspond with axes of the trachea and bronchi. To achieve this, head and neck are flexed to the left when examining the right bronchial tree and vice versa. Openings of all the segmental bronchi in both the lungs are examined in seriatim. Ref: Dhingra 7e pg 483