113 Cortical Thickness | Crouzon Imaging, Massachusetts General Hospital).23 The processing methodologies used by FreeSurfer have previously been validated and described in detail.24-26 Maps produced by FreeSurfer are not restricted by voxel resolution of the original data and are therefore able to detect submillimeter changes in cortical thickness as demonstrated by validation against histological analysis (within 0.07 mm and statistically indistinguishable from standard neuropathologic techniques) and manual mea-surements.27-30All T1-weighted images from the cohort were processed using the “auto-recon-all” pipeline in FreeSurfer. Estimates of vertex-wise cortical thickness were then generated by hemisphere and by cerebral lobes (ie, frontal, temporal, parietal, occipital, cingulate, and insula) as specified by the “--lobes” argument within the ‘mris_annotation2label’ command. Left and right hemisphere thickness outputs were averaged to generate a value for global cortical thickness. Similarly, lobar outputs from left and right hemispheres were averaged to generate a whole lobe thickness. Whole brain volume excluding ventricular volume was exported from FreeSurfer as ‘BrainSegVolNotVent’ via the ‘mri_segstats’ command. Statistical Analysis All data were imported into R statistical software (R Core Team, R version 3.6.1, 2019, Vienna, Austria) for analysis. Multivariate linear regression was first used to determine the level of variance in global thickness attributable to age at the time of MRI, sex, and whole brain volume. Multivariate analysis of covariance (MANCOVA) was then performed to assess these effects by lobe. Finally, multiple linear regression was used to determine associations between type of initial cranial vault expansion and lobar thickness while controlling for age and brain volume. A post-hoc power analysis was also performed to assess the quantitative limits of our current dataset. Cohen’s d with 95% confidence intervals were calculated as a secondary analysis to determine effect of suture-specific synostosis on underlying cortical lobes. Homogeneity of variance among suture-specific groups was evaluated by Levene’s test for age and χ2 for sex. RESULTS Patient Cohort Following review of medical and imaging records, 43 CP patients were identified. Six patients were excluded from further analysis since they did not undergo any primary vault expansion; either because they did not have synostosis (n = 2) or because of late referral and/or incomplete records (n = 4). An additional 3 patients underwent primary biparietal expansion and were also excluded. In total, 34 CP patients (19 men, 15 women) were therefore included in our cohort (mean ± SD age at the time of MRI of 8.9 ± 4.5 years). The interval between initial vault expansion and MRI was 7.1 ± 4.7 years. ICH was present in 8 (23.5%) patients preoperatively alone, 8 (23.5%) patients postoperatively alone, and 6 (17.6%) patients both pre and postoperatively. In 12 (35.3%) patients, no ICH was present. Birth weight data (range: 2920–4460 g; SD: 408 g) were 7
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