Measure of Frontal Morphology in Sagittal Craniosynostosis: The Frontal Bossing Index

Abstract

Background: Frontal bossing is a prominent forehead feature common in sagittal craniosynostosis (SC). Assessment of severity of frontal bossing is limited by the use of serial CT imaging or complex computer programing. Three-dimensional measurements of cranial surface morphology provide a radiation-free alternative for assessing cranial shape. This study describes the creation of a frontal bossing index (FBI), a novel tool using surface morphology to assess the frontal severity in patients with SC. Methods: Surface imaging from CT scans or 3D photographs of 359 individuals with sagittal craniosynostosis and 224 normocephalic individuals were compared to identify differences in frontal morphology. Cartesian grids were created on each individual’s surface mesh using equidistant axial and sagittal planes yielding 33 unique points of intersection on the forehead. Area under the curve (AUC) analyses were performed to identify frontal points with the greatest discrepancy between groups. Results: All points in the SC population had significantly greater protrusion than corresponding points in the control group. The largest differences were located in the superior lateral regions. Combining the superior- and lateral-most points gave the maximal AUC (0.9707) and was therefore selected to generate the frontal bossing index (FBI). The FBI distinguished between the 2 groups with a sensitivity of 93.5% and specificity of 92.9%. Conclusions: The frontal bossing index is a useful tool for evaluating the severity of the frontal region in patients with SC, comparing outcomes of differing surgical techniques, and tracking frontal changes in individuals over time, without the need for radiation.