170 Chapter 10 After all, extrinsic factors as FOHR, OSA and abnormal skull growth could be (surgically) treated. In conclusion: no evidence has been found for intrinsic brain or CBF abnormalities in non-operated patients with isolated metopic suture synostosis aged from 0-2 years. In non-operated syndromic craniosynostosis patients aged 0-2 years, microstructural parameters of the white matter tracts in syndromic patients are comparable to those of controls aged 0-2 years. Enlargement of the ventricles, measured by FOHR, play a significant role on microstructural properties. Part II. Are there any secondary effects of ICH and treatment on the brain of operated syndromic craniosynostosis patients, focusing on ventriculomegaly, chiari and cortical thickness? In syndromic patients we see a mechanical distortion of the brain and development of ventriculomegaly and/or cerebellar tonsillar herniation secondary to development of suture synostosis.16, 18, 36, 37 38, 39 To assess these secondary causes and/or effects of ICH in craniosynostosis patients, we undertook a longitudinal repeated measurement study to investigate the course of ventriculomegaly and the course of tonsillar herniation (TH) in Crouzon-Pfeiffer patients. Enlarged ventricles and the associated increase of intracranial pressure could cause damage to various brain regions, including white and grey matter.40-42 On the cause of hydrocephalus in syndromic craniosynostosis patients, many theories have been postulated. To date the most accepted theories are 1. venous hypertension caused by impaired venous outflow at the skull base and 2. overcrowded posterior fossa causing tonsillar herniation and inducing obstruction of CSF circulation.43, 44 However to date, no one unifying theory has been able to explain all variations of manifestations of hydrocephalus and TH. By investigating the course of ventriculomegaly, we discovered ventriculomegaly often presents before surgical treatment. The prevalence of tonsillar herniation increased as patients became older, even after the age of 5 years. Overall, in our study, the more common sequence is first occurrence of ventriculomegaly, followed by TH. One percentage point increase in FOHR was associated with a +1.6mm increase in tonsil position. The impact of tonsillar herniation seems unpredictable. It can cause symptoms and signs such as a headache, neck pain, ataxia, muscle weakness, altered sensation and dysphagia. Neurological functioning is used as a factor in surgical decision making on treating TH. 45, 46 However, Doerga et al. shows that, in craniosynostosis patients, the absence/presence of symptoms provides no diagnostic certainty in ruling-in or ruling-out normal cerebellar tonsillar position, or TH>5 mm and/or syringomyelia.47 The question arises how much of the treatment protocol should be focused on treating/ stabilizing TH in case it is not progressive and without symptoms.47-49 It would be helpful to identify a parameter that can predict which patient will develop TH and in
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