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Introduction: Craniosynostosis is typically corrected surgically within the first year of life through cranial vault reconstruction. These procedures often leave open calvarial defects at the time of surgery, which are anticipated to close over time in a large proportion of cases. However, residual calvarial defects may result as long-term sequelae from cranial vault remodeling. When larger defects are present, they may necessitate further reconstruction for closure.

Better understanding of the calvarial osseous healing process may help to identify which defects will resolve or shrink to acceptable size and which will require further surgery. Our study aims to assess the long-term changes in defect size after cranial vault reconstruction for craniosynostosis.

Methods: One-year postoperative and long-term computed tomography scans were retrieved from the craniofacial anomalies archive. Analysis used custom software. All defects above the size of 1 cm2 were analyzed and tracked for calvarial location, surface area, and circularity. Monte Carlo simulation was performed to model the effect of initial defect size on the rate of defect closure.

Results: We analyzed a total of 74 defects. The mean /- SD initial defect surface area was 3.27 /- 3.40 cm2. The mean /- SD final defect surface area was 1.71 /- 2.54 cm2. The mean /- SD percent decrease was 55.06% /- 28.99%. There was a significant difference in the percentage decrease of defects in the parietal and frontoparietal locations: 68.4% and 43.7%, respectively (P = 0.001). Monte Carlo simulation results suggest that less than 10% of defects above the size of 9 cm2 will close to the size of 2.5 cm2 or less.

Conclusions: We describe and make available a novel validated method of measuring cranial defects. We find that the large majority of initial defects greater than 9 cm2 remain at least 1 in2 in size (2.5 cm2) 1 year postoperatively. In addition, there appear to be regional differences in closure rates across the cranium, with frontoparietal defects closing more slowly than those in the parietal region. This information will aid surgeons in the decision-making process regarding cranioplasty after craniosynostosis correction.

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