Fig 3.

Segmentation by user-initialized 3D surface evolution (A). Limits for airway analysis are: (B, C) anterior, a vertical plane through posterior nasal spine perpendicular to the sagittal plane at the lowest border of the vomer; posterior, the posterior wall of the pharynx; lateral, the lateral walls of the pharynx, including the full extensions of the lateral projections; lower, a plane tangent to the most caudal medial projection of the third cervical vertebra perpendicular to the sagittal plane; (C, D) upper, the highest point of the nasopharynx, coinciding with the posterior choanae and consistent with the anterior limit.