Creation of the Scaphocephalic Index: Measurement of Global and Regional Severity in Scaphocephaly.

Background: The recently described frontal bossing index (FBI) and occipital bullet index (OBI) allow for quantification of scaphocephaly. A similar index examining biparietal narrowing has not been described. Addition of such an index measuring width would allow for direct evaluation of the primary growth restriction in sagittal craniosynostosis and the formation of an optimized global width/length measure.

Methods: Computed tomography scans and three-dimensional photographs were used to recreate scalp surface anatomy. Equidistant axial, sagittal, and coronal planes were overlaid, creating a Cartesian grid. Points of intersection were analyzed for population trends in biparietal width. Using the most descriptive point coupled with the sellion protrusion to control for head size, the vertex narrowing index is formed. By combining this index with the FBI and OBI, the scaphocephalic index (SCI) is created as a tailored width/length measure.

Results: Using 221 controls and 360 individuals with sagittal craniosynostosis, the greatest difference occurred superiorly and posteriorly at a point 70% of the head's height and 60% of the head's length. This point had an area under the curve of 0.97 and sensitivity and specificity of 91.2% and 92.2%, respectively. The SCI has an area under the curve of 0.9997, sensitivity and specificity greater than 99%, and interrater reliability of 0.995. The correlation coefficient between computed tomography imaging and three-dimensional photography was 0.96.

Conclusions: The vertex narrowing index, FBI, and OBI evaluate regional severity, while the SCI is able to describe global morphology in patients with sagittal craniosynostosis. These measures allow for superior diagnosis, surgical planning, and outcome assessment, independent of radiation.