Cerebrospinal Fluid Flow Impedance is Elevated in Type I Chiari Malformation

Abstract

Diagnosis of Type I Chiari malformation (CMI) is difficult because the most commonly used diagnostic criterion, cerebellar tonsillar herniation (CTH) greater than 3-5 mm past the foramen magnum, has been found to have little correlation with patient symptom severity. Thus, there is a need to identify new objective measurement(s) to help quantify CMI severity. This study investigated longitudinal impedance (LI) as a parameter to assess CMI in terms of impedance to cerebrospinal fluid motion near the craniovertebral junction. LI was assessed in CMI patients (N ¼ 15) and age-matched healthy controls (N ¼ 8) using computational fluid dynamics based on subject-specific magnetic resonance imaging (MRI) measurements of the cervical spinal subarachnoid space. In addition, CTH was measured for each subject. Mean LI in the CMI group (551 6 66 dyn/cm 5 ) was significantly higher than in controls (220 6 17 dyn/cm 5 , p < 0.001). Mean CTH in the CMI group was 9.0 6 1.1 mm compared to À0.4 6 0.5 mm in controls. Regression analysis of LI versus CTH found a weak relationship (R 2 ¼ 0.46, p < 0.001), demonstrating that CTH was not a good indicator of the impedance to CSF motion caused by cerebellar herniation. These results showed that CSF flow impedance was elevated in CMI patients and that LI provides different information than a standard CTH measurement. Further research is necessary to determine if LI can be useful in CMI patient diagnosis.

Spinal Fluid Biomechanics and Imaging: An Update for Neuroradiologists

“…2 Elastic properties of the tissues surrounding the subarachnoid space theoretically induce pressure waves, which to date are not fully characterized. 3 With contrast media or radionuclides in the spinal subarachnoid space, a slow convection of fluid is observed resulting from the continuous oscillation of CSF. 4 Viscous and inertial properties, together with the complex anatomy of the subarachnoid space, determine CSF flow patterns.…”

Neural Tissue Motion Impacts Cerebrospinal Fluid Dynamics at the Cervical Medullary Junction: A Patient-Specific Moving-Boundary Computational Model

“…This parameter has been reported to be useful in the assessment of CSF flow blockage at the CMJ and its value was measured to be greater in CM patients compared to controls 22, 29 . Results from this study show that the inclusion of CNS tissue motion increased the magnitude of ILI by ~20%.…”

“…To obtain the CSF flow at the CMJ, axial thru-plane PCMRI measurements were acquired at C2 22, 29 . In brief, a retrospective peripheral pulse-gated sequence with encoding velocity of 10 cm/s was used to obtain 20 images over the cardiac cycle.…”

“…In vitro 21, 23 and in silico modeling has been conducted with geometrically simplified 20 and subject-specific CMJ anatomy 14, 35 based on static geometry. These simulations provide a powerful tool for variational analysis to determine the importance of various anatomical features and properties and physiological functions on CSF dynamics such as: spinal cord nerve roots and denticulate ligaments 14, 30 , frequency and magnitude of CSF pulsations 17 , presence of arachnoid trabeculae 30 , focal spinal arachnoiditis 3 , tonsillar descent in CM patients 22, 29, 35 , spinal stenosis 21, 23 and properties of the spinal cord and dura in syringomyelia 6 . The engineering-based parameters are now being investigated to evaluate their potential for clinical use.…”

“…A CM patient was chosen for this study to maximize the impact that CNS tissue motion may have on CSF dynamics since the CSF spaces near the CMJ in Chiari patients are restricted in comparison to healthy subjects 22, 29 . Patient-specific CNS tissue motion of the spinal cord and cerebellar tonsils was measured by PCMRI and imposed in the CFD model as a rigid-walled moving boundary.…”