Unilateral coronal synostosis results in dysmorphology of the midface in addition to well-characterized cranial and orbital deformities. Because most American infants with this problem have undergone cranio-orbital surgery within their first year of life for the past 25 years, a paucity of data exist regarding the natural history of untreated unilateral coronal synostosis. In an attempt to remedy this void, an international search was conducted to identify computed tomography data sets of living individuals with untreated unilateral coronal synostosis; data were obtained from two European centers and one center in the United States. Results limited to the study of the midface are presented here. Digital data from high-resolution head computed tomography scans of 11 living, white individuals with untreated unilateral coronal synostosis were obtained from three craniofacial centers (in Denmark, The Netherlands, and the United States). Image volumes were constructed from each scan using ANALYZE biomedical imaging software. Fourteen pairs of three-dimensional distances were calculated on the ipsilateral (the side of the synostosis) and the contralateral (the side opposite to the synostosis) hemifaces using 11 osseous landmarks. The resulting measurements were expressed as a ratio of the ipsilateral: contralateral sides. Descriptive statistics were derived for the untreated unilateral coronal synostosis population and compared with analogous measurements performed on dried skulls. Age at computed tomography ranged from 1.1 to 21.1 years (mean, 6.6 years; median, 4.1 years). Twelve of the 14 measured distances differed by greater than 5 percent on the ipsilateral side, and all but one of these measurements were decreased on the ipsilateral side when compared with contralateral values. The results of this study support the following conclusions: (1) There are discrete and measurable differences in the facial morphology between patients with untreated unilateral coronal synostosis and normal skulls. (2) Intercenter and international collaboration can provide a sufficient number of individuals with rare craniofacial anomalies to quantitatively determine group characteristics. (3) Quantitative documentation of rare anomaly natural history is necessary for quantitative outcome assessment of treated patients.
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