Intracranial Volume After Cranial Vault Remodeling: To What Degree Does Intracranial Composition Change After Surgery?

Abstract

BACKGROUND: The intracranial cavity is composed of brain tissue as well as cerebrospinal fluid (CSF), blood, and air. These fluid components allow volume to be shunted out of the intracranial region in the setting of skull-based compression to minimize the effect of compression on the brain. The degree of change to the intracranial compartment in the setting of craniosynostosis and the speed at which they occur and resolve after surgery are not fully understood. This study sought to rigorously analyze the intracranial volume compositions of patients with craniosynostosis prior to and after CVR. METHODS: The authors compared volume measurements for age-matched patients with unicoronal (n = 4), metopic (n = 4), and sagittal (n = 4) craniosynostosis. Intracranial segmentation and analysis were performed on Materialize Medical 21.0 (Materialise; Leuven, Belgium) using the following segmentation thresholds: bone 226-3066 HU, CSF -281-18 HU, and air 19-225 HU, and then manually edited utilizing typical segmentation techniques. On expert consultation, brain segmentation volumes were determined to be less reliable measurements than intracranial, CSF, and air volumes and were thus calculated by subtracting the other volumes from ICV. Paired t tests, one-way analysis of variance, and multiple regression analyses were performed on STATA 15.1 (StataCorp, College Station, TX). RESULTS: The average age at surgical repair was 8.7 ± 0.83 months. All postoperative imaging was performed between 3 and 5 days postoperatively aside from one patient with imaging at 19 days postoperatively. There was a significant increase in total ICV (913772.5 ± 102480.5 mm3 versus 1068165 ± 95752.5 mm3; P < 0.001) and intracranial air volume (18608.8 ± 9639.1 versus 53230.2 ± 32607.4; P = 0.001) after CVR. On subgroup analysis by affected suture, there was a significant increase in ICV (851748.9 ± 87438.1 versus 1043117 ± 149763; P = 0.009) and brain volume (737312.3 ± 80166.5 versus 829060.9 ± 61405.6; P = 0.021) in the metopic cohort and a significant increase in ICV (1006379 ± 31359.5 versus 1133497 ± 45574.1; P = 0.013) and intracranial air volume (18056.21± 5397.634 versus 53230.16± 32607; P = 0.001) in the sagittal cohort. The metopic cohort had the largest percent change in intracranial volume (18% ± 3.4%) and CSF volume (28% ± 24%). There were dramatic postoperative increases in intracranial air volumes in all cohorts (percent change: unicoronal 46% ± 16%; sagittal 58% ± 36%, metopic 58% ± 23%) at this postoperative time period. On multiple regression analysis with affected suture, type of CVR, age at repair and time from surgery to postoperative imaging as independent variables, age at repair was the only significant predictor of percent change in ICV (coef, −5.35; 95% CI, −10.2 to −0.51; P= 0.04) at the 0.05 significance level. CONCLUSION: The ICV increase created by CVR allows subsequent increases in brain, CSF, and air volumes in the early postoperative time period. Significant brain tissue volume increases were seen in the metopic cohort with significant intracranial air volume increases in the sagittal cohort. We hope to perform additional analysis with follow-up data to determine if some of the noted air volume increase is redistributed to brain tissue or CSF at a later time.