The Creation Of A Frontal Bossing Index
Griffin Patrick Bins, M.D., Deborah Cull, B.S., Ryan Layton, B.S., Christopher Michael Runyan, MD PhD.
Wake Forest Baptist Health, Winston-Salem, NC, USA.
PURPOSE: Frontal bossing is an established descriptor of the morphology of patients with sagittal craniosynostosis (SCS). Attempts have been made to objectively quantify bossing; however, none have used imaging devoid of radiation exposure. As a result, clinical descriptions of preoperative and postoperative frontal bossing remain subjective or limited by aversion to serial radiation.
METHODS: Clinical computed tomographic scans and 3D stereophotograms of 360 patients with unoperated SCS and 225 normal patients from age 0 to 72 months were used to create 3D surface anatomy models. Ten equidistant axial and sagittal planes were created, and a Cartesian grid was formed by the intersection of these planes across the surface models. The distances between the points of axial/sagittal intersection overlaying the forehead and the mid-coronal plane were analyzed in order to quantify the difference in forehead protrusion between the two populations (F1). To control for age and sex, a ratio-based measure was used. The projection of the selion was selected as an internal control (F2).
RESULTS: In patients with SCS, increased protrusion was seen at all points on the forehead with the greatest differences present at the superior and lateral aspects (F3). Measures including all points, a subset of points, and individual pairs of points were analyzed. Area under the ROC curve (AUC) analyses were highest (0.96) when including only the two most distinct points (Axial level 5, Sagittal levels +3/-3). This measure yielded normal distributions for both the SCSS and the control populations. The sum of the ratios at both points yields the index score. A cutoff of 1.894 was selected and yields a sensitivity of 90.6% and specificity of 91.1% (F4). Score was not found to be confounded by imaging modality or sex. Age also showed no correlation in the control or SCS group except for individuals presenting late (> 24 months) with SCS who were observed to have less bossing.
CONCLUSIONS: The frontal bossing index (FBI) allows for objective quantification of frontal severity in the context of normative data for patients with sagittal craniosynostosis using only 3D photography or surface laser scanners available to nearly all clinicians, while obviating the need for serial radiation. This will guide surgical decision making and allow for greater accuracy in analyzing and comparing operative outcomes.
F3a and 3b:
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