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Surgical intervention for metopic synostosis is largely based on a subjective impression of the presence and severity of trigonocephaly. Several objective methods have been proposed to characterize phenotypic severity, but these methods are imprecise or impractical. The purpose of this investigation was to develop a practical and reliable quantitative method to assess trigonocephaly using computed tomographic (CT) data.Clinical and administrative databases were queried to identify sequential patients referred for evaluation of possible metopic synostosis. Age-matched comparative controls were selected from a previously described pediatric craniofacial normative database. Craniofacial CT data were assessed as two-dimensional axial series, three-dimensional reconstructions, and multiplanar reconstructions. Six methods were then evaluated for quantifying the interfrontal angle (IFA). Each method was critically appraised with respect to accuracy, precision, and practicality.Thirty-six (n = 36) sequential metopic cases and 107 normative controls were selected for analysis. Of the 6 methods assessed, the most reliable method involved measurement of the IFA formed between the anterior-most point of the cranium and the supraorbital notches using multiplanar reconstructions reoriented relative to the Frankfort horizontal plane. With this method, mean (SD) normal and metopic IFAs were found to be 144.8 (8.5) degrees (range, 125.3–159.7 degrees) and 117.74 (9.0) degrees (range, 92.3–136.8 degrees), respectively. Age and sex did not significantly affect the IFA. Intraobserver and interobserver variances were 0.90 and 0.94, respectively. Receiver operating characteristic analysis showed an area under the curve of 0.986, indicative of an excellent diagnostic test.Measurement of the IFA as described is an accurate, precise, and practical quantitative measure for the diagnosis of trigonocephaly.