Assessment of Cranial Sexual Dimorphism Using 3D Reconstruction: Implications for Gender-Affirming Surgery

Abstract

Background: As more centers offer gender-affirming procedures, dissemination of best practices is critical to ensuring quality care. This study is the first to use advanced 3-dimensional visualization software to characterize cranial differences between natal males and females, as they relate to planning for facial gender-affirming operations. Materials and Methods: A retrospective analysis was conducted on randomly selected patients with facial computed tomography imaging performed at a single institution between February 2020 and July 2021. Patients with acquired bony deformity on computed tomography or documented history of hormone replacement therapy were excluded. The images were retrieved and analyzed using advanced 3-dimensional visualization software (Vitrea). Independent sample t tests were performed to analyze variation in typically sexually dimorphic facial features between natal males and females. Results: We identified 50 patients (25 natal males and 25 natal females) who met the inclusion criteria. Ages ranged from 19 to 91. Natal males were found to have significantly greater frontosellar distances (difference between means, SEM: 2.7±1.2; P=0.03) and mandible volumes (difference between means, SEM: 14.0±4.2; P=0.002) than natal females. Statistical analysis revealed no significant differences in gonial angle, chin width, nasofrontal angle, or nasolabial angle between natal males and females. Conclusion: In this diverse sample of natal males and females, statistical analysis revealed that the sexually dimorphic facial characteristics most relevant to the planning of facial gender-affirming surgery are frontosellar distance and mandible volume. When planning facial gender-affirming surgery, we recommend that these characteristics be considered to achieve optimum results.