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Volumetric Changes in Cranial Vault Expansion: Comparison of Fronto-orbital Advancement and Posterior Cranial Vault Distraction
Christopher A. Derderian, M.D.1, Jennifer L. McGrath, B.S.2, Scott P. Bartlett, M.D.2, Jesse A. Taylor, M.D.2.
1UT Southwestern Medical Center, Dallas, TX, USA, 2University of Pennsylvania, Philadelphia, PA, USA.

PURPOSE:
Traditionally, we have relied heavily upon fronto-orbital advancement (FOA) as our primary means of achieving gains in intracranial volume to treat syndromic craniosynostosis. Posterior cranial vault expansion using distraction osteogenesis (PVD) has recently been introduced and is believed to provide greater gains in intracranial volume than FOA. The purpose of this study is to provide quantitative volumetric analysis of patients who underwent either FOA or PVD to determine the true gains in intracranial volume produced by each procedure.
METHODS:
This was a retrospective study of pre- and postprocedure CT scans of two groups of 6 patients each with syndromic bicoronal craniosynostosis who underwent reconstruction with either FOA or PVD were reviewed. CT data were analyzed volumetrically with 3D Slicer software to delineate the intracranial space, from which three-dimensional volume renderings of the intracranial space were created and volumetric measurements in mm3 were calculated before and after FOA (Figures 1-2) and PVD (Figures 3-4) Craniometric measurements of the cranial base from external acoustic meatus to external acoustic meatus were performed. The ratio of the preoperative and postoperative measurements served as a control for volume gains attributable to growth.
RESULTS:
The difference in volume between the preoperative CT scan and immediate postoperative CT scan ranged from 53mm3-190mm3 for FOA and 131-366 mm3 for PVD. A ratio of this volume difference and preoperative CT scan represented the total percent volume change that ranged from 6.7-22.1% for FOA and 16.1-48.9% for PVD. To correct for volume change attributable to growth alone a correction factor derived from preoperative and postoperative skull base measurements was applied to the these values. The mean percent volume increase for FOA was 8.6% (range 5.6-13.8%, S.D. 2.8) and the mean percent volume increase for PVD was 16.5% (range 12.4-25.7, S.D. 4.8), for a mean percent difference of 7.9% (p=0.04)
CONCLUSION:
Posterior cranial vault distraction is a powerful tool that provides significant intracranial expansion and improvement in head shape through correction of occipital flattening. The preliminary findings of this study indicate that PVD provides significantly greater intracranial volume gains than conventional FOA. This greater volume expansion is compelling evidence to consider the use of PVD as the initial vault expansion procedure in all syndromic patients when appropriate.


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