Mandibular dysmorphology in unicoronal synostosis and plagiocephaly without synostosis

Abstract

Patients with unicoronal synostosis (UCS) or plagiocephaly without synostosis (PWS) have distinctive skull dysmorphologies. Associated mandibular dymorphologies have been suspected but not quantified. This study was performed to test the hypothesis that discrete mandibular dysmorphology exists in both UCS and PWS. All patients at a tertiary referral center at a medical school-affiliated children's hospital with confirmed diagnosis of UCS or PWS with adequate pretreatment CT data were included in the study population, which population was comprised of 20 UCS, 23 PWS, and 8 normal infants. Each patient had a head CT scan using 2-mm slices. 3-D images were created using Analyze, a biomedical imaging program. The mandibles were isolated, and the coordinates of 8 landmarks were sampled from each mandible by a single investigator: a single volume value was measured, and 9 linear distances and 4 angles were calculated. Corresponding measurements from each hemimandible were expressed as ratios of ipsilateral/contralateral side. In UCS, the affected side was defined as the side ipsilateral to the synostosis; In PWS, the affected side was defined as the side ipsilateral to the occipital flattening. The results from both groups were t tested for statistical significance. For UCS, statistically significant (p < .001) findings included: ipsilateral hemimandibular volume 5% smaller than contralateral; affected hemimandibular body length 1.9% shorter; affected gonial angle 2.6% more acute; affected coronoid process tilted anteriorly 2.5%; and distances from condylion and tip of the coronoid process to the chin landmarks 4% shorter on the affected side. For PWS, significant findings included: affected hemimandibular volume 3.8% larger; ramal height 3.5% shorter; mandibular body length 3% longer; and coronoid process tilted anteriorly by 2.3% on the affected side. In the UCS/PWS comparison, findings included: affected hemimandibular volume in UCS 8.7% less; affected gonial angle in UCS 3% more acute; affected mandibular corpus length in UCS 5% shorter; distances from the condylion and the tip of the coronoid process to the chin landmarks 4% shorter on the affected side in UCS. The hypothesized presence of diagnosis specific mandibular dysmorphology in UCS and PWS is confirmed. This analysis forms the baseline for study of the effects of unperturbed growth or therapeutic interventions upon the dentoskeletal dysmorphology of these anomalies.