PURPOSE: Craniosynostosis results from premature fusion of the cranial sutures and leads to distortion of normal calvarial anatomy. It has long been understood that this distortion is a direct result of growth restriction adjacent to the synostotic suture with compensatory growth of adjacent structures; however, there has been a paucity of data regarding volumetric assessment, by quadrant, of calvarial asymmetry. This study aims to characterize cranial vault asymmetry in patients with unicoronal craniosynostosis focusing on posterior cranial vault volumetric changes. Additionally, we will quantify the effect of distraction osteogenesis (DO) on established cranial asymmetry.
MATERIALS AND METHODS: Retrospective chart review at Rady Children’s Hospital identified 17 patients with unilateral craniosynostosis who underwent cranial vault reconstruction by internal DO. Pre- and postdistraction computerized tomography scans were analyzed using ITK-SNAP volume segmentation software. These 3-dimensional reconstructions were bisected into hemispheres by a midsagittal plane from nasion to occipital crest, and into anterior and posterior quadrants based on a coronal plane between the anterior take off of the petrosal ridges. Quadrant and hemispheric volumes were compared pre- and post-DO using paired Student’s t tests.
RESULTS: Seventeen patients were analyzed (4 males, 13 females, age 6–32 months) over a 5-year period. Before DO, the synostotic posterior quadrant (SPQ) contained 1.9% less volume as (a proportion of total intracranial volume [ICV]) compared to the nonsynostotic posterior quadrant (NSPQ) (27.3% versus 29.2%; P = 0.039). Likewise, the synostotic anterior quadrant (SAQ) contained 4.3% less volume than the nonsynostotic anterior quadrant (NSAQ) (19.6% versus 23.9%; P = 0.0019). There was no significant difference in the proportion of hemispheric volumes before or after surgery (synostotic: 48.5% versus 51.4%, P = 0.2; nonsynostotic: 43.5% versus 51.5%; P = 0.1). Following cranial distraction, total ICV increased by 27.5% (95% confidence interval, 14.9%–34.6%) with an absolute mean volume increase of 216.5 cm3 (848.5 versus 1,065 cm3). ICV change after distraction was more significant in the SAQ (mean, 34.8%) and SPQ (27.6%) compared to the contralateral quadrants (NSAQ 18.3% and NSPQ 19.4%). Despite this fact, when assessing the change in volume as a proportion of total ICV, there was no significant difference between pre- and post-DO volumes in the SPQ (27.3% versus 26.6%; P = 0.57), NSAQ (23.9% versus 23.6%; P = 0.81), or NSPQ (29.2% versus 27.9%; P = 0.21). The SAQ did show a statistically significant increase of 1.2% (19.6% versus 21.8%) following DO with a relative increase of 11.2% (P = 0.036). Postdistraction, the SAQ and SPQ contained 1.8% (48.5% versus 51.4%; P = 0.2) and 1.3% (48.5% versus 51.5%; P = 0.1) less volume than the NSAQ and NSPQ, respectively.
CONCLUSIONS: Unilateral coronal craniosynostosis leads to ICV restriction in the ipsilateral posterior quadrant in addition to the expected restriction in the SAQ, resulting in ICV asymmetry of both the anterior and posterior cranial vault. After DO, there is an increase and redistribution of ICV that is most notable in the quadrants ipsilateral to the fused coronal suture. This redistribution results in an overall improvement in cranial vault symmetry; however, minor restriction in growth of the SAQ and SPQ persists as compared to their contralateral counterparts.