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An Analysis of Mandibular Volume in Hemifacial Microsomia

Background: The mandibular deformity in hemifacial microsomia is characterized by ramus-condyle unit deficiency. The Pruzansky score classifies the proximal mandible according to aberrant condylar-unit structure. The authors sought to volumetrically evaluate the hemifacial mandible compared with controls, and to assess for Pruzansky score correlation. Methods: This is a retrospective analysis of children with hemifacial microsomia. Demographic information was obtained, and computed tomographic data were analyzed by segmentation and volumetric calculations. Age-matched controls were compared using the t test. Results: Computed tomographic scans revealed 24 hemifacial and 13 controls: 62.5 percent right, 12.5 percent left, and 25 percent bilateral; and 34 percent type I, 28 percent type IIa, 16 percent type IIb, and 22 percent type III. Type IIb/III compared with type I/IIa were 11,100 and 17,773 mm3, respectively (p = 0.0029). Segmental evaluation of type IIb/III versus type I/IIa showed 3590 versus 6510 mm3 for the proximal segments (p = 0.0022) and 7449 versus 10,829 mm3 for the dental-bearing segments (p = 0.0221). All hemifacial microsomia hemimandibles (types I to III) were significantly less than controls: 14,837 versus 20,418 mm3 (p = 0.0005). Both dentate and proximal hemifacial microsomia segments statistically decreased in volume with increasing Pruzansky score. The dentate segment of the unaffected hemifacial microsomia side was statistically less than controls. Conclusions: This study volumetrically characterized the hemifacial microsomia mandibular deformity. As expected, with increasing Pruzansky severity, hemimandibular and proximal segment volumes declined. Unexpectedly, the hemifacial dentate segment also proved significantly diminished, corresponding to the degree of proximal volume loss.