Subject-specific variability in cerebrospinal fluid flow characteristics through cerebral aqueducts in a healthy population: a magnetic resonance imaging and computational investigation.

Ventricular cerebrospinal fluid (CSF) flow has bi-directional flow profiles synchronized with cardiac pulsation. The increase in CSF stroke volume through the aqueduct (flow pathway between the third and fourth ventricle) is believed to be a biomarker of idiopathic normal pressure hydrocephalus (iNPH). However, several studies have reported that CSF stroke volume varies considerably even in healthy populations. To explore these variations from a fluid mechanics perspective, this study analyzed CSF flow characteristics in healthy individuals using magnetic resonance imaging (MRI)-based computational simulations. MRI data from 47 healthy subjects were acquired, and the maximum Reynolds number of the CSF flow through the aqueduct and the degree of CSF mixing were evaluated. Results showed that the Reynolds number of the CSF flow through the aqueduct was 28.6 ± 13.3, and the limited variation suggested fluid mechanical similarities of CSF flow characteristics in the healthy population. A positive correlation between CSF flow mixing and the Reynolds number was observed in both healthy populations and iNPH patients. These findings demonstrate that CSF flow through the aqueduct, especially in healthy populations, can be well characterized by examining fluid mechanical similarities.