Normal mandibular growth and diagnosis of micrognathia at prenatal MRI

ObjectiveThe aim of this article is to present reference data for fetal mandibular growth on magnetic resonance imaging, enabling the diagnosis of micrognathia. MethodsRetrospectively, on 355 magnetic resonance scans of apparently facially normal fetuses [gestational age (GA), 20-36weeks], mandibular anterior-posterior diameter (APD=mandibular size), inferior facial angle (IFA=mandibular position), and jaw index (APD normalized to biparietal diameter) were correlated with GA by Pearson correlation. APD-age relationship was modeled. A receding chin was subjectively determined. Ten fetuses with mandibular anomalies were compared with normal fetuses. ResultsFor GA, APD showed high correlation (r=0.850; P<0.001), IFA (r=0.086; P=0.119) no correlation, and jaw index (r=-0.139; P=0.018) weak correlation. APD-age relationship was expressed by the following: APD=0.281+0.989*GA (r(2)=0.723). A receding chin was identified in 7/10 abnormal fetuses. APD, IFA, and jaw index of abnormal and normal fetuses were significantly different (P<0.001). In 10/10 abnormal fetuses, IFA was <50.0 degrees; in 7/10, jaw index wasless than the fifth percentile (micrognathia); in 3/10, jaw index was at low normal range (retrognathia). ConclusionsSubjective identification of micrognathia may be limited. Reference data provide quantitative evaluation of mandibular size and position. An IFA <50 degrees reflects micrognathia or retrognathia; a jaw index less than the fifth percentile suggests micrognathia. (c) 2014 John Wiley & Sons, Ltd.