Skull Base Asymmetry Evaluation in Non-Syndromic Patients using 3D Imaging

Objectives: Facial asymmetry has been classified into (1) mandibular body asymmetry, (2) mandibular elongation and condylar lengthening, (3) maxillary and mandibular asymmetry including c-shaped facial morphology. The underlying etiology and determinants of asymmetric facial growth is unclear. We examined the skull base anatomy for correlation with the type of facial asymmetry. Methods: We examined 40 patients: 18, 16, and 6 in groups 1, 2, and 3 respectively. Bilateral skull base landmarks were identified on 3D reconstructions of cone beam CTs (CBCT) using Invivo5 (Anatomage, San Jose, CA). The coordinate system for measurements was based on the mid-sagittal plane (MSP) defined by nasion, anterior clinoid process, and basion and the horizontal plane defined by right orbitale and porion. Landmarks included: mandibular fossa (MF), carotid canal (CC), foramen spinosum (FS), foramen ovale (FO), foramen lacerum (FL), stylomastoid foramen (SMF), and hypoglossal canal (HC). The shortest distance from these points on each side to MSP was measured and compared. Paired and unpaired t-tests were used for statistical analysis. Results: The average difference in distance of anterior landmarks (MF, FS, FO, FL) from MSP on both sides was greater in group 3 though not statistically significant likely due to sample size. In group 3, skull base landmarks were farther away from MSP on the side with mandibular elongation. Statistically significant difference was found between groups 3 and 1 and groups 3 and 2 when comparing distance of MF from MSP (P<0.05). Conclusions: A systematic method has been established to study skull base anatomy using 3D imaging. Greater anterior skull base asymmetry was found in the more severe maxillary/mandibular and c-shaped facial asymmetry compared to mandibular only asymmetries. The effect of skull base development on facial morphology as identified on 3D CBCT may lead to early diagnosis and optimized treatment in the future.