Leakage or diversion of cerebrospinal fluid (CSF) is associated with a variety of displacements of nervous tissue that may affect the brain, spinal cord and nerve roots. The displacements may be classified by the site of the leak - spinal canal or cranial cavity - and by whether the displacements are global, affecting wide regions of the nervous system, or local, affecting only nervous tissue adjacent to the leak. We propose a common pathophysiology for these displacements. A leak or a shunt results in an abnormal spatial pattern of CSF flow governed by abnormally directed hydrodynamic forces that act upon the submerged nervous tissue to propel it towards the site of the leak or the orifices of the shunt. We argue that the hydrodynamic mechanism causing displacement is distinct from the physical mechanisms responsible for other frequent manifestations of CSF leak, such as orthostatic headache, low recumbent CSF pressure, and dilation of dural veins. The existence of distinct mechanisms allows understanding of how the effects of CSF loss may differ in patients with spinal CSF leak and patients with ventricular shunts. It clarifies many variant cases where some of the characteristic manifestations of CSF leak may be absent. We discuss the roles of abnormal hydrodynamic forces in the variety of presentations subsumed under the term “slit ventricle syndrome” and consider the therapeutic implications of the proposed pathophysiological mechanism.