Three-dimensional cerebrospinal fluid flow within the human central nervous system

Abstract

This work describes a three-dimensional (3D) numerical simulation of the flow field of the complete enclosed Central Nervous System (CNS) including the ventricular system, the spinal cord and spinal sub-arachnoid space (SAS). Previous works on the topic consider only parts of the complete system imposing artificial boundary conditions at internal cross sections. The computational domain was constructed from MRI data using Materialise Software Mimics. In this work pulsatile velocity inlets in the lateral ventricles, due to the cardiac cycle, were used to simulate the dynamic nature of the CSF, whilst pressure outlets were used to model the areas of CSF re-absorption. A porous medium formulation (Darcy flow) was considered in the SAS to account for the effect of the arachnoid trabeculae within these areas. The simulation was run using the commercial CFD code Fluent using the laminar solver and transient simulation. A maximum CSF velocity was found to be in the region 11.8 mm/s, with a peak pressure drop through the aqueduct of the order of 2.8 Pa corresponding to a calculated peak Reynolds number of 12. CSF pressure at the exits of Magendie and Luschke were found to vary over the cardiac cycle, with pressure at the exits of Luschke being higher than Magendie for large periods of the cycle. CSF was seen to enter the SAS as a laminar jet from the exits of Magendie and Luschke. By only considering the cardiac cycle a very slow CSF motion within the spinal SAS was observed with magnitudes significantly reduced after a depth of 50mm down the column from the exit of Magendie. This result suggests that pulsating wall motion in the region of the spinal cord, due to respiratory effects, needs to be considered in order to predict experimentally observed flow recirculation within the spinal sac. 287 words.