title: Normal mandibular growth and diagnosis of micrognathia at prenatal MRI.
abstract: OBJECTIVE
  The aim of this article is to present reference data for fetal mandibular growth on magnetic resonance imaging, enabling the diagnosis of micrognathia.
  
  
  METHODS
  Retrospectively, on 355 magnetic resonance scans of apparently facially normal fetuses [gestational age (GA), 20-36 weeks], 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.
  
  
  RESULTS
  For 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°; in 7/10, jaw index was less than the fifth percentile (micrognathia); in 3/10, jaw index was at low normal range (retrognathia).
  
  
  CONCLUSIONS
  Subjective identification of micrognathia may be limited. Reference data provide quantitative evaluation of mandibular size and position. An IFA <50° reflects micrognathia or retrognathia; a jaw index less than the fifth percentile suggests micrognathia.
authors.affiliation: Department of Biomedical Imaging and Image-guided Therapy, Division of Neuroradiology and Musculoskeletal Radiology, Medical University of Vienna, Vienna, Austria.
authors.forename: Ursula
authors.initials: U
authors.lastname: Nemec
authors.forename: Stefan F
authors.initials: SF
authors.lastname: Nemec
authors.forename: Peter C
authors.initials: PC
authors.lastname: Brugger
authors.forename: Michael
authors.initials: M
authors.lastname: Weber
authors.forename: Bernhard
authors.initials: B
authors.lastname: Bartsch
authors.forename: Dieter
authors.initials: D
authors.lastname: Bettelheim
authors.forename: Michael
authors.initials: M
authors.lastname: Gruber
authors.forename: Daniela
authors.initials: D
authors.lastname: Prayer
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008334:Mandible / Q000196:embryology*; D008844:Micrognathism / Q000175:diagnosis*; D011247:Pregnancy; D012016:Reference Values; D012189:Retrospective Studies; D016216:Ultrasonography, Prenatal; D055815:Young Adult