A model of pulsations in communicating hydrocephalus.

The traditional theory of communicating hydrocephalus has implicated the bulk flow component of CSF motion; that is, hydrocephalus is generally understood as an imbalance between CSF formation and absorption. The theory that the cause of communicating hydrocephalus is malabsorption of CSF at the arachnoid villi is not substantiated by experimental evidence or by physical reasoning. Flow-sensitive MRI has shown that nearly all CSF motion is pulsatile, and there is substantial evidence that hyperdynamic choroid plexus pulsations are necessary and sufficient for ventricular dilation in communicating hydrocephalus. We have developed a model of intracranial pulsations based on the analogy between the pulsatile motion of electrons in an electrical circuit and the pulsatile motion of blood and CSF in the cranium. Increased impedance to the flow of CSF pulsations in the subarachnoid space redistributes the flow of pulsations into the ventricular CSF and into the capillary and venous circulation. The salient features of communicating hydrocephalus, such as ventricular dilation, intracranial pressure waves, narrowing of the CSF-venous pressure gradient, diminished cerebral blood flow, elevated resistive index and malabsorption of CSF, emerge naturally from the model. We propose that communicating hydrocephalus is the result of a redistribution of CSF pulsations in the cranium.