Paradoxical Mandibular Growth Pattern in Craniofacial Microsomia Patients

Mandibular growth in craniofacial microsomia characteristically favors the affected side. However, we have observed the opposite growth pattern in a minority of patients. Here, we describe four patients with facial features of hemifacial microsomia which showed a paradoxical growth pattern (occlusal plane remained level and the mandible did not shift to the side with the short ramus).

The purpose of this study was to analyze unusual mandibular growth patterns in subjects with hemifacial microsomia using measurements from panoramic radiographs and cone beam computed tomography (CBCT) scans. We will test the hypothesis that changes in mandibular body length compensated for the differences in ramal height.

Four subjects treated at Childrens Hospital Los Angeles (3 male and 1 female) age ranging from 4 to 17 years were found to have this paradoxical growth pattern.  The subjects underwent a three dimensional analysis using NewTom 9000 CBST scans for: Ramal length (Co-Go) and body length (Go-Mid-symphysis) were measured on the affected and unaffected sides and mandibular length (Co-Mid-symphysis). These measurements were compared to control groups of hemifacial microsomia patients with similar ramal height deficiency, but who lacked the paradoxical growth pattern.

Sample size consists of four patient with paradoxical hemifacial microsomia and four age matched controls with conventional hemifacial microsomia and similar ramal height deficiecy. Mean length of follow up was 4 years. The 3dct measurements were assesed, means and standard deviations were calculated for each group, a two-tailed student's t-test was performed, with *p <0.05 considered significant. All data was assessed by three blinded independent observers.

The panoramic radiographs showed that in the affected side, the mandibular body was longer than the unaffected side mandible body in patients with paradoxical growth. This difference in body length was not observed in the control group. Further there was no gap between the glenoid fossa and top of the affected ramus. The glenoid fossa tended to be in a lower vertical position on the affected side in patients with the paradoxical growth pattern.

Patients with paradoxical growth showed lengthening of the mandibular body on the affected side rather than the unaffected side and the glenoid fossa was lower on the affected side. This unusual pattern of growth could compensate for a congenitally short ramus and keep the occlusal plane level. Patients with this type of paradoxical growth pattern express a less severe phenotype of hemifacial microsomia.

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