OBJECTIVE This study was conducted to design a rational approach to the MR diagnosis of hydrocephalus based on a pathophysiologic reevaluation of its possible mechanisms and to apply it to the different etiological contexts. METHODS A review of the literature reports describing new physiologic models of production and absorption and of the hydrodynamics of the CSF was made. RESULTS Besides the secretion of CSF by the choroid plexuses, and its passive, pressure-dependent transdural absorption (arachnoid villi, dural clefts, cranial, and spinal nerve sheaths), water transporters, aquaporins, allow water (if not ions and organic molecules) to exchange freely between the brain parenchyma and the CSF spaces across the ependymal and the pial interfaces (including the Virchow-Robin spaces). Consequently, the CSF bulk flow is not necessarily global, and situations of balanced absorption-secretion may occur separately in different CSF compartments such as the ventricular, intracranial, or intraspinal CSF spaces. This means that rather than from a hypothetical pressure gradient from the plexuses to the dural sinuses, the dynamics of the CSF depend on the force provided in those different compartments by the arterial systolic pulsation of the pericerebral (mostly), intracerebral, and intraventricular (choroid plexuses) vascular beds. CONCLUSIONS Using MR imaging, diverse varieties of hydrocephalus may tentatively be explained by applying those concepts to the correspondingly diverse causal diseases. Hopefully, this may have an impact on the choice of the treatment strategies also.