Three-dimensional Coordinate System for Hemifacial Microsomia

Background: Hemifacial microsomia (HFM) is a congenital disorder characterized by facial asymmetry, but no midline reference has been established for evaluating facial morphology in patients with HFM. The purpose of this study was to develop a 3-dimensional coordinate system unaffected by the deformity of the external acoustic aperture or orbital circumference and to quantitatively evaluate craniofacial morphology in such patients. Methods: We quantitatively evaluated craniofacial morphology using 3-dimensional measurements with the skull base as a reference. Using computed tomography data from 15 patients with HFM and 15 controls, a coordinate system was created for each patient, and left-right differences between measurement points were compared. Results: When mandibular deformity was severe, the deformity of the posterior part of the palatine bone and lateral part of the orbit increased, but this trend was not evident for other measurement points. Thus, craniofacial deformity in HFM was not always related to mandibular deformity. Moreover, no difference was evident in the position of the hypoglossal canal between controls and patients with HFM. Conclusions: Quantitative assessments are possible using the coordinate system devised in this study, irrespective of the severity of HFM. The degree of mandibular deformity detailed in the Pruzansky classification was associated with the superoinferior deformity of the posterior part of the palatine bone and anteroposterior deformity of the lateral part of the orbit.