132 Chapter 8 METHODS The medical ethics committee of the Erasmus MC approved this study (MEC20171143). This retrospective study gives an overview of children with Crouzon syndrome treated at the Erasmus MC in Rotterdam, the Netherlands, Sophia Children’s Hospital, the national referral hospital for patients with syndromic craniosynostosis. It serves an approximately 3.6 million national pediatric population.13 Patients were included sequentially from June 1994 to October 2019, DNA analysis confirmed Crouzon syndrome. As part of our clinical protocol,4 we perform surgical vault expansion before 1 year of age. First choice is occipital expansion with springs, scheduled around the age of 6–5 months. If ventriculomegaly develops before this age, vault expansion is scheduled earlier. When hydrocephalus appears after vault expansion, a shunt or endoscopic third ventriculostomy (ETV) will be considered. If initial ventricular enlargement following a cranial vault expansion is not progressive, an expectant policy is followed. If ICH occurs, a second vault expansion is preferred over shunting. In general, a shunt is avoided before or shortly after cranial vault expansion to prevent skull growth reduction. Brain Imaging As per clinical protocol, magnetic resonance imaging (MRI) exams were obtained at first presentation (usually before 1 year old), at 2 and 4 years old, and additionally when clinically indicated. All MRI data were acquired using a 1.5 Tesla MR Unit (General Electric Healthcare, Milwaukee, Wisc.). Images were aligned in sagittal and coronal planes using Philips 3D-modeling in Intellispace software, to ensure measurements were done consistently and in the correct plane. Computed tomography (CT) scans were acquired using a multidetector CT-scanner (Siemens, Erlangen, Germany). Scan protocol parameters were set to obtain image quality required for clinical interpretation. Patients underwent at least one CT-scan during follow-up before surgery, to determine which cranial sutures were closed. Additional CT-scans were done only when clinically indicated, to minimize radiation exposure. Fronto-occipital horn ratio (FOHR) was used as parameter for ventricle size. FOHR is calculated as (frontal horn width + occipital horn width)/biparietal diameter*2 and gives a ratio of ventricle size that can be interpreted independent of age.14, 15 An FOHR ≥ 0.4 was considered ventriculomegaly. FOHR was determined on MRI or CT-scans. Children with hydrocephalus underwent VP-shunt/ETV. The tonsil position was determined as the position of the lowest cerebellar tonsil in mm above (referred to as negative numbers) the foramen magnum (FM) or below the
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