134 Chapter 8 Correlation between repeated measurements of the same child was taken into account by including a random (patient specific) intercept. An analogous model, but assuming a normal distribution, was fitted to investigate the association between tonsil position and FOHR, head-circumference, and lambdoid suture synostosis at the age of less than 1 year. Because FOHR, tonsil position, and head-circumference were measured at different time points, values of the independent variables had to be imputed at the time points the dependent variable was observed. To this end, we estimated both mixed-models in the Bayesian framework, which allowed us to simultaneously impute the missing observations by specifying additional mixed-models for each of the independent variables. Specifically, the model for FOHR was estimated jointly with random intercept linear mixed-models (with natural cubic splines for age) to impute head-circumference and TH, and the model for TH was fitted jointly with a random intercept beta mixed-model for FOHR and a linear random intercept model for head-circumference (both with a natural cubic spline for age). We assumed vague priors for all parameters. Results of the Bayesian models are presented as posterior mean and 95% credible intervals (CI). RESULTS Patient Characteristics Sixty-three Crouzon patients were included in this study, patient characteristics are presented in Table 1, and genetic changes are mentioned in Supplemental Digital Content 1, which displays genetic changes present in this cohort of Crouzon patients). Median age at presentation was 0.9 (IQR 0.2–3.0) years; median follow-up at study conclusion was 10.2 (IQR 4.3–15.7) years. Ventriculomegaly and TH Development and Progress over Time. Figure 1 shows factors TH ≥ +5mm and FOHR ≥ 0.4 preoperatively and postoperatively in the 63 children, categorized by the moment at which TH ≥ +5mm occurred. In patients with both ventriculomegaly and TH ≥ +5mm (n = 18), TH ≥ +5mm was detected before ventriculomegaly occurred in one of 18 patients, TH ≥ +5mmwas detected after ventriculomegaly occurred in five of 18 patients, and TH ≥ +5mm and ventriculomegaly were detected at the same time in 12 of 18 patients. In four patients TH ≥ +5mm was detected after placement of a VP-shunt; in two patients TH ≥ +5mm was detected after ETV. Thirteen patients underwent VP-shunting or ETV: 10 patients were initially treated with a vault expansion followed by VP-shunt, and in three patients the order of procedures was the other way around. Patient-specific trajectories of FOHR and tonsil position are displayed in Figure 2. The trajectories show the distinct differences between patients in development and progress of FOHR and tonsil position.
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