Ipsilateral Hypertrophy of the Mastoid Process in Surgical Cases of Congenital Muscular Torticollis

Objective: This study was to investigate ipsilateral hypertrophy of the mastoid process in the patients with congenital muscular torticollis (CMT). Design: Retrospective cross-sectional study. Patients: Children with CMT. Methods: A total of 212 surgical cases of patients with CMT (age: 50.9 ± 44.3 months) and 212 age- and gender-matched controls (age: 50.4 ± 44.2 months) were included. The mastoid process volume was calculated and compared for both groups on the computed tomography axial images. A linear regression analysis was performed between the age and the intrasubject volume difference in the mastoid process. Results: The volume of the mastoid process in the CMT side was significantly larger than that of the non-CMT side in the CMT group (32.2 ± 30.3 cm³ vs 21.9 ± 22.8 cm³; P <.001). In the control group, there was no significant difference between the volume of the right and left mastoid process (21.6 ± 24.6 cm³ vs 21.2 ± 23.8 cm³; P =.472). The intrasubject volume difference in the mastoid process in the CMT group showed a linear increase with the age (adjusted R² = 0.286; P <.001), and the volumetric asymmetry of the mastoid process became more severe over age compared to the control group. Conclusion: We showed ipsilateral hypertrophy of the mastoid process in patients with CMT and demonstrated that the volumetric asymmetry increased with age.