Quantification of Bony Depression in Mastoid Region After Expander Implantation for Microtia Reconstruction in Hemifacial Microsomia

Object: Three-stage expansion method represents the most common form of microtia reconstruction in hemifacial microsomia (HFM). Although the complication related expander has lowered owing to the current advances, bony depression in mastoid region in microtia patients with hemifacial microsomia was observed in clinical work. The aim of this study was to quantify bony depression after retroauricular expander implantation and identify associated factors. Methods: 42 patients were enrolled and studied prospectively utilizing 3-dimensional (3D) evaluation. Craniofacial computed tomography (CT) was performed before the first (pre-expansion) and the second stage (post-expansion) and 3D quantification was done to quantify bony depression in mastoid region by using CT data. Univariate analysis was performed to identify factors associated with bony depression in mastoid region. Results: The mean level of mastoid depression was 0.83 mm (range: 0.07-4.08 mm), and the max level of mastoid depression was 1.40 mm (range: 0.20-6.65 mm). In univariate analysis, capsular duration of expansion and expansion volume were associated factors with mastoid depression. Conclusion: This study showed the possibility of mastoid depression following expander implantation for microtia reconstruction in hemifacial microsomia. Plastic surgeons should be aware of the possibility and associated factors of bony depression in mastoid region following expander implantation to optimize microtia reconstruction for patients with HFM.