Abstract: CT Analysis of Micrognathia: Do Cephalometrics Predict Management Course?

Abstract

INTRODUCTION: Mandibular micrognathia is the primary defining characteristic of Pierre Robin Sequence (PRS) that sets off a physiologic cascade with varying severity of airway obstruction.1 The diagnosis of micrognathia is predominantly clinical, though with the advent of three-dimensional computed tomography (3D-CT), the development of objective and accurate measurements of skeletal morphology could be a useful clinical adjunct for management.2 The aim of this study is to investigate the efficacy of using cephalometric analysis to guide clinical management: non-operative treatment, mandibular distraction, tracheostomy. METHODS: Records were retrospectively reviewed from 2004–2016 (IRB#2011-0247). Infants less than one year of age with PRS, evaluated for surgical management of micrognathia with a CT scan were included. 3D-CT analysis of total mandibular length (Co-Gn) and total midface length (Co-A) was performed in addition to traditional cephalometric analysis – Co-Gn, Co-A, SNA, SNB, ANB – in reformatted sagittal CT scans. Clinical data collected included age at CT scan, sex, and associated syndromic status. Chi-squared and Kruskal-Wallis tests were used to compare values among patients that were managed non-operatively, with mandibular distraction osteogenesis (MDO), and tracheostomy at any point, with Mann-Whitney U test reserved for comparing two groups. RESULTS: 147 patients met inclusion; 33 non-operative, 73 MDO, 41 tracheostomy. CT scans were performed at an older age in the tracheostomy group compared to the non-operative and MDO groups (96.3, 58.3, 39.4 days, respectively; p=0.02). Likewise, the tracheostomy group had a greater proportion of syndromic patients compared to non-operative and MDO groups (76%, 36%, 40%, respectively; p=0.0003). Traditional cephalometric measures demonstrated no differences among the groups: Co-Gn (non-operative: 43.0mm, MDO: 41.2mm, tracheostomy: 41.1mm; p=0.17), Co-A (41.7, 40.7, 41.5mm, respectively; p=0.28), ANB (18.1°, 19.2°, 20.3°, respectively; p=0.37), SNA (84.3°, 83.0°, 84.0°, respectively; p=0.46), and SNB (66.1°, 63.8°, 63.6°, respectively; p=0.14). 3D-CT analysis of total mandibular length (46.3, 46.2, 45.2mm, respectively; p=0.48) and total midface length (49.3, 48.5, 48.5mm, respectively; p=0.37) did not differ among groups. CONCLUSION: Cephalometric measurements from computed tomographic scans did not differ among patients that were managed non-operatively, underwent mandibular distraction, or tracheostomy. These results illustrate the limitation of solely using skeletal data as a means to predict the need for surgical intervention for airway compromise. Reference Citations: 1. Pruzansky S, Richmond JB. Growth of Mandible in Infants with Micrognathia Clinical Implications. Archives of Pediatrics & Adolescent Medicine. 1954;88(1):29. doi:10.1001/archpedi.1954.02050100031005. 2. Breugem CC, Evans KN, Poets CF, et al. Best Practices for the Diagnosis and Evaluation of Infants With Robin Sequence. JAMA Pediatrics. 2016;170(9):894. doi:10.1001/jamapediatrics.2016.0796.