13 Introduction makes a small ICV less likely to be associated with ICH.18-22 However, restricted growth with deviation in the skull OFC growth curve demonstrates to be an important clinical sign that indicates the impending or presence of ICH.23 21Also studies on the base of the skull have been undertaken, finding that the foramen magnum is smaller in sCS patients than in controls. This smaller foramen magnum may play a role in the development of ventriculomegaly and ICH. 24-29 30 27, 29 Brain tissue Focusing on brain tissue, De Jong et al. showed that brain volumes of sCS patients were not different compared to normative data at ages 1, 4, 8 and 12 years.31 Also cerebellar volume has been found to be the same in sCS patients compared to control subjects.20, 27 Intracranial blood The cerebral blood volume is a dynamic intracranial compartment, which is under physiological control by autoregulation, but also carbon dioxide level and venous outflow play a role. Vasodilatation effect of OSA Obstructive sleep apnea (OSA) is also noticeable contributor to increased cerebral blood volume in children with craniosynostosis.16 32 OSA leads to carbon dioxide retention during obstructive episodes, which causes vasodilatation and subsequently raised ICP.16 In children with multisuture or syndromic craniosynostosis, there may be a high prevalence of OSA, around 70%. The prevalence and severity are highest in patients with Apert, Crouzon and Pfeiffer syndrome.33-38 This moderate-severe OSA occurs mostly in Apert and Crouzon patients, due to midface hypoplasia with/without mandibular hypoplasia. Impaired venous outflow The jugular foramina are skull apertures fromwhich blood outflows from the intracranial compartment. The jugular foramina of sCS patients were shown to be smaller than in controls, which could cause impaired intracranial venous outflow and venous vascular collateral adaptation. Apart from Muenke syndrome, this adaption of emissary veins is seen more often in sCS patients than in normal controls. 27, 39, 40 Because patients with Muenke syndrome rarely have ICH, the relation between emissary veins and ICH implies to be more presumable. The mutation in the fibroblast growth factor receptor (FGFR) gene might also contribute to impaired venous outflow, by affecting the premature endothelial proliferation and subsequent differentiation of the sigmoid and jugular sinuses. This results in a narrowed vascular lumen of these sinuses.41, 42 1
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