The physics of hydrocephalus.

This article reviews our previous work on the dynamics of the intracranial cavity and presents new clinically relevant results about hydrocephalus that can be gained from this approach. Simulations based on fluid dynamics and poroelasticity theory are used to predict CSF flow, pressures and brain tissue movement in normal subjects. Communicating hydrocephalus is created in the model by decreasing CSF absorption. The predictions are shown to reflect dynamics demonstrated by structural MRI and cine-MRI studies of normal subjects and hydrocephalus patients. The simulations are then used to explain unilateral hydrocephalus and how hydrocephalus could occur without CSF pulsations. The simulations also predict the known pressure/volume relationships seen on bolus infusions of CSF, and the small transmural pressure gradients observed in animal experiments and in patients with hydrocephalus. The complications and poor performance of shunts based on pressure-sensitive valves are explained and a system of feedback control is suggested as a solution.