Ontogenetic Trends in Frontal Sinus Shape

Abstract

Adult frontal sinus morphology has been studied in biological anthropology, both in terms of its function and variation. Overall, this structure is known to be highly variable among individuals, to such an extent that it is used to make positive identifications in the medicolegal setting. However, very little is known about the growth and developmental processes leading to the wide ranges of frontal sinus size and shape. Although several studies investigate frontal sinus ontogeny in terms of size and linear dimensions, much less is known regarding the ontogeny of its shape. This study partially addresses this gap by examining frontal sinus outlines using longitudinal radiographic data to evaluate when the frontal sinus attains its adult shape.Longitudinal radiographs for 107 individuals (57M/50F) spanning 5–29 years of age (yoa) were obtained from the AAOF Craniofacial Growth Legacy Collection ( www.aaoflegacycollection.org). Superior borders of frontal sinus outlines were digitally traced in ImageJ; the superior orbital border demarcated inferior sinus boundaries. Age of first appearance was also recorded. A total of 749 outlines were imported into SHAPE‐software, where elliptical Fourier (20 harmonics) and principal components (PC) analyses were conducted. PC1 (49.18% variation explained) reflects height‐to‐breadth relationships, while PC2 (11.74%) reflects asymmetry in right versus left lobe dominance.To assess when the frontal sinus attains its adult shape, Euclidean distances of PCs 1–9 (91.58% cumulative variance) between each age point and the 18‐year point were calculated within individuals; this process was repeated for the 20‐year point. Scatterplots with Loess curves for each distance plotted against age suggest adult shape is attained around 20yoa. Sexual dimorphic trends are evident in the Loess curves, whereby males exhibit greater distances from 20yoa at early ages. An analysis of variance confirms these sex‐based differences (F=7.063, P<0.0001); Tukey post‐hocs further suggest that while adult females are not significantly different in shape from adult males or younger females/males (13–19yoa), adult males are significantly different from males 15yoa and younger. T‐tests failed to find significant sex‐based differences for age‐of‐first‐appearance (t=1.482, P=0.142) and adult‐shape (PC1: t=−0.670, P=0.505; PC2: t=1.827, P=0.058). Thus, it appears that while both sexes display similar start times in sinus development and reach similar adult‐shapes, females attain their adult shape sooner. This suggests a slower developmental process in males. Additional studies are needed to determine how these ontogenetic patterns in 2D sinus‐shape relate to the overall size and 3D dimensions of the sinus.