Nose-skull relationships for craniofacial identification: computed tomography (CT) assessment of nose width, nasal bridge shape & pronasale position

The nose is one of the primary facial features assessed from skulls when undertaking craniofacial identification. While several nose estimators have been published, out-of-group tests are relatively few. In this study, we use high-resolution CT scans and a pool of 92 Australian adults to assess three previously published nose estimation models: (1) nose width estimated from the maximum width of the nasal aperture; (2) nasal tip curve (inferior oblique view) estimated from the superior nasal aperture shape; and (3) pronasale position estimated from two-tangents according to recent revisions. Tests of Method 1 in 63 subjects reveal standard errors of the estimate (SEE) of 4.0 mm. Tests of Method 2 in 31 carefully screened subjects produced a Procrustes distance (d) of 0.24. Tests of Method 3 in 43 subjects, yielded a SEE of 10 mm for Euclidean distances between the estimated and ground truth pronasale position. Cartesian coordinate error (x/y) for the latter method, revealed pronasale was placed too far antero-inferiorly in most subjects (x = +2.2 mm and y = -6.2 mm). These results indicate that current published nose estimation models often yield noses with substantially incorrect dimensions for all three factors: nose width, nose tip curve and position of the nose tip. To improve the established methods, we propose a correction factor (sign-reversed mean error) that delivers a calibration-in-the-large for the estimation models helping to increase their accuracy.