Longitudinal impedance (LI) is a scalar parameter to quantify impedance or resistance to cerebrospinal fluid (CSF) motion in the spinal canal near the foramen magnum (FM). LI was estimated in patients with Chiari malformation type 1 (CM) with and without specific symptoms.
Fifteen CM patients were divided into two groups: nonspecific-CM (NS-CM) – patients with non-cough related symptoms (5/15) and specific-CM (S-CM) – patients with either severe cough-related headache, myelopathy, syringomyelia, or muscle atrophy (10/15). Inner and outer boundaries of the cervical spinal subarachnoid space between the FM and 6cm caudal to the FM were segmented, smoothed and reconstructed. 3D model ends were extruded 4cm to allow the flow to be nearly fully developed inside the model. An unstructured tetrahedral mesh was created. Finite volume solver was utilized to run the fluid simulation. Boundary conditions included an unsteady velocity at the inlet to represent the cardiac cycle and CSF flow, a constant pressure at outlet, and rigid walls with no slip conditions. LI was calculated by dividing fast Fourier transform (FFT) of the pressure change between the FM and 2.5cm caudal to the FM by the FFT of volume flow rate and integrating between 1-8 Hz.
Although the mean integrated LI for S-CM was 71% larger than NS-CM (1102 ± 547.5 and 645.7 ± 484.6, p = 0.13 respectively), this difference was not statistically significant. Integrated LI for NS-CM cases increased linearly with respect to tonsillar position (r = 0.99, p = 0.001). However, LI for S-CM cases were scattered and not significantly correlated to tonsillar position (r = 0.08, p = 0.83).
Discussion and Conclusion
Integrated LI between S-CM and NS-CM was not significantly different. A larger sample size is required to determine if CSF resistance is indicative of CM symptom severity