The Effects of Cranial Orientation on Forensic Frontal Sinus Identification as Assessed by Outline Analyses

Abstract

The utility of frontal sinuses for personal identification is widely recognized, but potential factors affecting its reliability remain uncertain. Deviations in cranial position between antemortem and postmortem radiographs may affect sinus appearance. This study investigates how slight deviations in orientations affect sinus size and outline shape and potentially impact identification. Frontal sinus models were created from CT scans of 21 individuals and digitally oriented to represent three clinically relevant radiographic views. From each standard view, model orientations were deviated at 5° intervals in horizontal, vertical, and diagonal (e.g., left-up) directions (27 orientations per individual). For each orientation, sinus dimensions were obtained, and outline shape was assessed by elliptical Fourier analyses and principal component (PC) analyses. Wilcoxon sign rank tests indicated that sinus breadth remained relatively stable (p > 0.05), while sinus height was significantly affected with vertical deviations (p < 0.006). Mann-Whitney U tests on Euclidean distances from the PC scores indicated consistently lower intra- versus inter-individual distances (p < 0.05). Two of the three orientations maintained perfect (100%) outline identification matches, while the third had a 98% match rate. Smaller and/or discontinuous sinuses were most problematic, and although match rates are high, practitioners should be aware of possible alterations in sinus variables when conducting frontal sinus identifications.

Keywords: computed tomography; elliptical Fourier analysis; frontal sinus shape; human identification; outline analysis; radiology.

Figure 1

Standard cranial views utilized in this study from left to right: Orbitomeatal Line (OML), Frankfort Horizontal Plane (FHZ) and Porion-Alveolar Line (PAL). Dashed line represents the axial plane of orientation, see text for details.

Figure 2

Graphical representation of the nine varying 5-degree orientations used in each view. Frankfurt Horizontal Plane pictured. Note actual 2D images used for analyses did not include the cranium.

Figure 3

PC1 (top), PC2 (middle), and PC3 (bottom) values plotted against vertical orientations (left) and horizontal orientations (right) for each view; circles with same color scheme represent the same individual across all graphs (legend provided). PC contours also provided, with thick blue lines representing constructed +2 standard deviations (above) and −2 standard deviations (below) relative to the mean; black dashed lines representing actual outlines from an individual near the extremes of the axes. D, down; S, straight; U, up; R, right; L, left.

Figure 4

Sinus area (top), height (middle), and breadth (bottom) plotted against vertical orientations (left) and horizontal orientations (right) for each view: Orbitomeatal Line (OML), Frankfort Horizontal Plane (FHZ), and Porion-Alveolar Line (PAL). Circles with same color scheme represent the same individual across all graphs (legend provided). D, down; S, straight; U, up; R, right; L, left.

Figure 5

Percentage histogram of multivariate PC inter- and intra-individual distances for Orbitomeatal Line (OML; top); Frankfort Horizontal (FHZ; middle) and Porion-Alveolar Line (PAL; bottom) views.

Figure 6

Box and whisker plots illustrating medians and quartiles for intra-individual distances for each individual in the three views: Orbitomeatal Line (OML), Frankfort Horizontal Plane (FHZ), and Porion-Alveolar Line (PAL).

Figure 7

Outlines of the two mismatched individuals (TC1154, TC1155).

Figure 8

Example of individual (TC1110) outlines with relatively high intra-distances in the Orbitomeatal Line (OML) view (0.25–0.30) (see Figure 8 histogram); note the loss of the anatomical-right lobe and tail (large arrow), as well as the loss of the smaller anatomically left-sided arcade (small arrow), in the inferiorly oriented (Down) views. This drastically alters shape outline from two almost discontinuous lobes to a single plateau-like lobe. Outlines represent the normalized elliptical Fourier coefficients (based on 20-harmonics and aligned by the first harmonic).