Objectives: Nasopharyngeal (NP) depth prediction is clinically relevant in performing medical procedures, and enhancing technique precision and safety for patients. Nonetheless, clinical predictive variables and normative data in adults remain limited. This study aimed to determine normative data on NP depth and its correlation to external facial measurements. Methods: A multicenter cross-sectional study obtained data from adults presenting to otolaryngology clinics at five sites in Canada, Italy, and Spain. Investigators compared the endoscopically measured depth from sill to nasopharynx along the nasal floor to the facial measurements “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 CT images were available, the distance from the nasopharynx to nasal sill was also collected. Results: 371 patients participated in the study (41% women; 51 years old, SD 18). The average endoscopic depth 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 to 0.86). Perpendicular distance was strongly correlated to NP depth (r=0.775; p<0.001), with an average underestimation of 0.1 cm (SD 0.65; 95% CI 0.06 to 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 to 0.16). Conclusions: Nasopharyngeal depth can be accurately approximated by the distance from the tragus to a plane perpendicular to philtrum. The generated predictive equation was most accurate but not likely clinically relevant.
