Assessment and Identification of Improvement Areas for Facial Symmetry in Hemifacial Microsomia (Type IIB) Using Three-dimensional Measurements.

Abstract

Surgical planning for hemifacial microsomia (HFM) patients often involves planning the amount of maxillary movement and mandibular bone distraction from three-dimensional (3D) volumetric images constructed from computed tomography scans. By representing anatomical indicators for facial symmetry in X, Y, and Z coordinates, we identified the more challenging areas in correcting facial asymmetry. The study included five HFM patients with a mean age of 22.2 years, all diagnosed with HFM (type IIB). We established measurement points with high reproducible 3D coordinates on the 3D volumetric images obtained from computed tomography scans for before surgery, treatment objectives, and after surgery. We assessed the symmetry of measurement points between the affected side and nonaffected side at each time point. In the before-surgery group, significant differences were observed between the affected side and nonaffected side in X,Y (excluding Palatine foramen, upper molar, canine) and Z coordinates for measurement items. In the treatment objectives group, no differences were observed between the affected side and nonaffected side in X, Y, and Z coordinates, resulting in facial symmetry. In the after-surgery group, significant differences were observed in Y coordinates in the mental foramen area, and significant differences were observed in z axis measurement items in the canine and mental foramen areas. It is evident that relying solely on a front view assessment is insufficient to achieve facial symmetry. Particularly, both anterior-posterior and vertical improvements in the area near the mental foramen on the affected side are necessary.