How deep do you go? Clinical prediction of nasopharyngeal depth based on facial measurements

Nasopharyngeal depth (ND) prediction is clinically relevant in performing medical procedures, and in enhancing technique accuracy and patient safety. Nonetheless, clinical predictive variables and normative data in adults remain limited. This study aimed to determine normative data on ND and its correlation to external facial measurements. A multicenter cross-sectional study obtained data from adults presenting to otolaryngology clinics at five sites in Canada, Italy, and Spain. Investigators compared endoscopically measured depth from the nasal sill (soft tissue between the nasal ala and columella) to nasopharynx along the nasal floor to the "curved distance from the alar-facial groove along the face to the tragus" and "distance from the tragus to a plane perpendicular to the philtrum." When sinus computed tomography images were available, the distance from the nasopharynx to the nasal sill was also collected. 371 patients participated in the study (41% women; 51 years old, SD 18). Average ND was 9.4 cm (SD 0.86) and 10.1 cm (SD 0.9) for women and men, respectively (p < 0.001; 95% CI 0.46-0.86). Perpendicular distance was strongly correlated to ND (r = 0.775; p < 0.001), with an average underestimation of 0.1 cm (SD 0.65; 95% CI 0.06-0.2). The equation: ND (cm) = perpendicular distance*0.773 + 2.344, generated from 271 randomly selected participants, and validated on 100 participants, resulted in a 0.03 cm prediction error (SD 0.61; 95% CI -0.08-0.16). Nasopharyngeal depth can be approximated by the distance from the tragus to a plane perpendicular to the philtrum.