S7B-06 SESSION 7B: HFM ROBIN - PART II QUANTITATIVE ANALYSIS OF MASSETER MUSCLES IN PATIENTS WITH HEMIFACIAL MICROSOMIA

Abstract

Introduction: To measure the volumes of the masseter on both sides of Hemifacial Microsomia (HFM), test the difference between the masseter muscles on the affected and unaffected side, analyze the correlation of the asymmetry degrees between the masseter and the mandible, and test whether the asymmetry of masticatory muscle can be judged by the OMENS classification. Methods: 198 patients (mean age 4.5 years old) with HFM were studied using three-dimensional reconstruction computed tomography data. The height of mandible ramus and volumes of masseter muscles on both sides were measured. Asymmetry was expressed as the (unaffected- affected) / (unaffected + affected) *2. Results: The mean volumes for affected and unaffected masseters were 4.23 cm3 and 8.41 cm3 respectively. The asymmetry of masseter and mandible is 80.20% and 36.11%, respectively. Masticatory muscle volumes were significantly implicated in hemifacial microsomia. It shows a strong correlation between the volume of the masseter muscle and the height of ipsilateral mandible ramus. 9.1% (18/198) masseter muscle was absent which has significant relevance with the mandible deformity. No significant correlation was observed between the degrees of asymmetry of the masseter muscle and the soft tissue grade in OMENS classification. Conclusion: In HFM the masseter has a smaller volume on the affected versus unaffected side strongly related to the degrees of mandible malformation. Finally, the severity of masticatory muscle disproportion can probably not be judged by soft tissue standards in OMENS classification.