Fig. 4
Endoscopy of the nasal cavities in the left nostril (a), the right nostril (b), the lumen near the opening (c), and the deepest site (d) of the middle nostril. a and b The lumen of the right nostril is narrower compared with that of the left nostril. c The mucosa is smooth and pale pink in the lumen of the middle nostril. d The blind-ended structure (asterisk) is observed approximately 5 cm deeper than the opening of the middle nostril