The Physics of Hydrocephalus

Abstract

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.

Compression-sensitive magnetic resonance elastography

“…2 Along the head-feet axis. 3 From the ears toward the center of the brain hydrocephalus [38,51,69,93]. In this study, the properties of the slow compression wave predicted by the Biot model [8] in the low-frequency range (< 70 Hz) were analyzed in healthy volunteers to assess and quantify volumetric strain effects in the brain with and without external mechanical stimulation, following pioneering work on poroelastic data analysis of cerebral MRE by Perriñez et al [71,72] and Pattison et al [68].…”

Ventricle Equilibrium Position in Healthy and Normal Pressure Hydrocephalus Brains Using an Analytical Model

“…In addition, no consistent differences were evidenced between all the waves due to cardiac or respiration cycles. In an experimental study, Penn et al [8] did measurements before, during and after both acute and chronic hydrocephalus induced by intracisternal injection of kaolin in dogs. They could not either find pressure gradients between the ventricles, brain parenchyma, and SAS greater than the resolution of the sensors (0.5 mm Hg).…”

“…Excluding this small effect of arteries and veins, the parenchyma provides little elasticity to abrupt deformation. However, in long term, the flow and absorption of ISF within the interconnected channels could be the primary compliance source [8,19].…”

“…A difference in timing between the pulsatile wave in the SAS and the ventricles could act as a driving force for enlargement. However, no detectable pressure difference in the waves was found in several experimental studies [2,7,8]. Several studies have been carried out experimentally to elucidate the unclear mechanism of NPH [9][10][11].…”

Brain biomechanics during acute obstructive hydrocephalus in live rats

“…Predicted transmantle pressure gradients are not found in humans or in animals with hydrocephalus [1,2]. We hypothesize that pulsatile forces transmitted through incompressible cerebrospinal fluid (CSF) into viscoelastic brain tissue results in slowly accumulating strain that leads to subsequent ventricular enlargement.…”