Figure 1.

Pharyngeal airway space sub-regions division with posterior nasal spine (PNS) as the anterior vertical limit and pharyngeal soft tissue contour as the posterior limit. Red color indicates nasopharyngeal region extending from root of clivus superiorly to PNS inferiorly. Green color indicates oropharyngeal area extending from PNS superiorly to anterior–inferior point of the body of third cervical vertebrae (C3ai) inferiorly. Yellow color indicates hypopharyngeal region extending from C3ai superiorly to anterior–inferior point of the body of fourth cervical vertebrae inferiorly (C4ai).