114 Chapter 7 also collected, and no patients were found to be of low enough weight (<1500 g) to impact thickness development as reported in previous studies.31, 32 Additionally, birth weight was found to be evenly distributed between both treatment groups and among all sutural involvement subgroups. Primary Cranial Vault Expansion Before assessing any effect of primary cranial vault expansion type on cortical thickness, we determined the level of variance explained by age, sex, and brain volume. Multivariate linear regression showed that these three variables accounted for 40% of the variance in cortical thickness (R2 = 0.40), with univariate analyses yielding R2 for age, sex, and brain volume as 0.39, 0.01, and 0.06, respectively. Further evaluation by lobe using MANCOVA yielded a Pillai trace test statistic of 0.64, 0.17, and 0.24 for age, sex, and brain volume, respectively. Univariate results of the MANCOVA test by lobe are available in Table 1. Of the 34 patients, 13 (7 male, 6 female, median age at MRI 5.1 yrs) underwent occipital expansion as a primary procedure. 21 patients (12 men, 9 women, median age at MRI 11.5) underwent primary frontal expansion. Multiple linear regression did not find a correlation between global cortical thickness and primary cranial vault expansion type (Table 2). Primary occipital expansion was associated with a 0.02 mm thicker cortex globally (l = 0.02, 95% CI −0.12 to –0.15, P = 0.82), as well as thicker frontal (l = 0.02, 95% CI −0.15 to –0.20, P = 0.78), parietal (l = 0.06, 95% CI −0.09 to –0.20, P = 0.44), and occipital (l = 0.05, 95% CI −0.10 to –0.19, P = 0.51) lobar cortices. Also, in the occipital expansion group, there was an association with thinner temporal (l = −0.03, 95% CI −0.16 to –0.10, P = 0.68), cingulate (l = −0.04, 95% CI −0.29 to –0.22, P = 0.78), and insular (l = −0.09, 95% CI −0.36 to –0.17, P = 0.48) cortices. l-coefficients and 95% confidence intervals for each region are shown in Figure 1. Lastly, power analysis revealed the need for a cohort size of 59 patients to detect a 0.2 mm change in thickness at a level of 80%. Our cohort in this study was 80% powered to detect a 0.37 mm difference between surgical treatment groups.
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