171 General Discussion whom it will be progressive and symptomatic. 50 More strict cut off values for shunting in case of ventricular enlargement may be identified. Previous studies demonstrate varying levels of cortical thinning and grey matter reduction related to the severity of hydrocephalus, in both children and animal models. Increasing ventricle size is associated with decreased neurodevelopment.51, 52 Wilson et al. show almost two-thirds of patients with Crouzon-Pfeiffer syndrome develop ICH, and they exhibit—on average— global cortical thinning.35 To prevent and/or treat ICH in patients with Crouzon-Pfeiffer syndrome, patients undergo cranial vault expansion. We studied the potential influence of frontal and occipital primary vault expansions on cortical thickness in the brain regions of the expanded skull. In this study we did not find a difference in the effect between frontal and occipital primary vault expansions and cerebral cortical thickness (regional or global). Next, we looked for local or regional effects related to synostosis pattern. The lambdoid synostosis could have a local effect or a more general effect by playing a role in crowding of the posterior fossa, which could affect venous and CSF outflow obstruction, which subsequently may cause intracranial hypertension in Crouzon patients.53 In our study we did not observe local effects on the occipital lobes. However, widespread thinning was associated in patients who had synostosis of one or both lambdoid sutures, in which the greatest effect was seen in the cingulate and frontal lobe. These generalized effects and distant regional effects may be an effect of general ICH or this may be because of a varying degree of ICH sensitivity within the cortical regions of the brain. If there is a varying degree of sensitivity to ICH within brain regions, this may have to do with the different timing in myelination per brain region. Wilson et al. revealed that detection of hydrocephalus or papilledema was independently associated with significant changes in cortical thickness.35 At the Erasmus MC, fundoscopy and optical coherence tomography (OCT) are commonly used to screen for ICH. Given the correlation between papilledema and cortical thinning, it appears to be important to detect ICH at an earlier stage, even before papilledema can be detected. Because of the complexity of the pathogenesis of ICH in syndromic patients, further assessment on contributing factors is necessary. Moving towards a more preventative approach, screening on ventricular volume or CBF may prove to be valuable. Future studies should investigate these methods of ICH detection. One of the compensatory mechanisms of ICH is the development or expansion of venous collaterals. The first, not yet published, pilot data of the Erasmus MC craniofacial research group show a strong relation: a high FOHR relates to a high systematic score on collaterals. Collaterals are identified on the first MRI scan and seem not to change over time in this pilot study. Even after shunt placement and improvement of FOHR, collaterals are still identified in the same way as earlier identified on the MRI scan. 10
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