Fig. 1.

Standard model of CSF circulation and hydrocephalus pathology. a) Standard model of CSF circulation in the adult human brain. Hydrocephalus is characterized by enlargement of the cerebral ventricles classically attributed to dysregulated CSF flow, leading to overaccumulation of CSF that distends the ventricles and raises the intracranial pressure. Neurosurgical CSF diversion that aims to reduce CSF volume and intracranial pressure is the primary treatment strategy for hydrocephalus. Image modified from Servier medical art (https://smart.servier.com) permitted by the creative commons attribution license (https://creativecommons.org/licenses/by/3.0/). b) Clinical case that demonstrates an example wherein the standard model of CSF circulation does not sufficiently explain the pathogenesis of hydrocephalus. Patient is a 3-year-old girl who presented with progressive macrocephaly. Neuroimaging prior to surgery (top panels) demonstrated extreme communicating ventriculomegaly with strikingly turbulent CSF flow and small cerebral cortex. A ventriculoperitoneal shunt was placed to divert CSF from the ventricles into the peritoneal cavity. Postoperative imaging showed complete resolution of CSF turbulence with persistence of ventriculomegaly. Although the patient’s progressive macrocephaly was arrested, she continued to exhibit mild neurocognitive impairments. Thus, reinstatement of CSF homeostasis may address some consequences of disease and prevent further deterioration but does not necessarily target the underlying developmental pathology. Images from patient were modified with permission from (Duy and Kahle 2021).