Mid-sagittal MRI in a normal subject highlighting the four upper airway regions

A) Nasopharynx, which is defined from the nasal turbinates to the hard palate; B) retropalatal (RP) oropharynx extending from the hard palate to the caudal margin of the soft palate, C) retroglossal (RG) region from the caudal margin of the soft palate to the base of the epiglottis; and D) hypopharynx, which is defined from the base of the tongue to the larynx.