Measurement of each parameter on lateral neck X-ray. Hypopharynx width (A, B): the width of the hypopharyngeal air column at the mid-height of the second cervical vertebral body. Epiglottic width at the tip (C, D): the anteroposterior (AP) diameter of the epiglottis at 5 mm from the tip. Epiglottic width at the base (E, F): the widest AP diameter of the epiglottis measured at or above a line drawn through the base of the epiglottis perpendicular to a line that bisects the vallecula. Retropharyngeal soft-tissue thickness (G, H): the prevertebral soft-tissue thickness at the mid-height of the 3rd cervical vertebral body. Third cervical vertebral body width (H, I): the AP diameter of the 3rd cervical vertebral body measured at the mid-height of the vertebral body. Aryepiglottic fold (J, K): the largest width of the aryepiglottic fold. Retrotracheal soft tissue thickness (L, M): the prevertebral soft-tissue thickness at the mid-height of the sixth cervical vertebral body.