Three-dimensional symmetry of the midfacial skull: A cross-sectional CT morphometric analysis comparing mirroring and best-fit alignment

INTRODUCTION: This study assessed midfacial skeletal symmetry in healthy individuals using advanced image segmentation and three-dimensional analysis. It aimed to quantify left-right symmetry and evaluate potential influences such as age and sex. Two methods were compared: mirroring with best-fit alignment (BFA) and rigid median sagittal plane mirroring (MSP). It was hypothesised that BFA provides a more accurate assessment of symmetry, and demographic variables do not significantly affect asymmetry. METHODS: A retrospective cross-sectional study, conducted in accordance with STROBE guidelines, analysed high-quality midfacial CT scans acquired between 2018 and 2024. Inclusion criteria required intact anatomy without fractures or bone pathology. The primary outcome measures were root mean square (RMS) and mean absolute distance (MAD), which quantified deviations between MSP and BFA. Additional parameters included left-right volumes and surface areas, and their absolute and relative differences were calculated. RESULTS: A total of 102 CT scans met the inclusion criteria. Significant differences between MSP and BFA were observed for both RMS and MAD across all structures. Median differences ranged from 0.94 to 1.56 mm (RMS) and 0.90-1.63 mm (MAD). Bland-Altman analysis revealed systematic deviations between methods. Multiple logistic regression identified several parameters as significantly associated with sex, suggesting possible sex-related morphological influences on symmetry. Except for the orbital floor, at least 75% of individuals showed relative side-to-side differences of ≤ 5%. CONCLUSION: Although statistically significant differences between MSP and BFA were identified, absolute deviations were minute. Most individuals demonstrated high bilateral symmetry, with relative differences of ≤ 5% for most structures.