Study of spinal cord poroelastic behavior under Chiari Malformation conditions: A computational fluid dynamics study

Chiari malformation (CM) is a rare neurological condition characterized by the herniation of cerebellar tonsils through the foramen magnum. Almost 40-75% of patients with CM develop a syrinx, a fluid-filled cavity inside the spinal cord. The characteristics of the pathology and clinical experience linked the development and resolution of the syrinx to the disrupted fluid dynamics. However, this mechanism has not been fully understood yet. Poroelasticity is a powerful instrument to model porous tissues like the spinal cord. However, only a few studies using this physic to study the CM relate syringomyelia can be found in the literature. Therefore, the objective of this thesis was to investigate the poroelastic behavior of the spinal cord under CM conditions. Mainly with a focus on the fluid dynamics in the SAS and on the spinal cord response. The firs study focused on poroelasticity. It highlighted the effect of geometry, permeability, Young’s modulus, and Poisson’s ratio on the material swelling. It indicated the time needed to establish a flow through the material, allowing the optimization of numerical settings for the computational modeling. Based on the results of the first study, an idealized 2D axisymmetric model of the spinal cord and spinal subarachnoid space was built to assess the influence of different parameters (inlet and permeability) on spinal cord behavior. Various physiological situations were simulated by applying different inlet conditions. The results highlighted the influence of the inlet pressure wave frequency (coming from the skull) on the poroelastic material's response. Higher frequencies, related to higher cardiac frequencies, coughing, sneezing or Valsalva’s maneuvers, showed to increase the response’s magnitude. Changes in material permeability presented a nonlinear relation between this property and the volumes oscillations of the syrinx. However, the mechanism behind this relationship is not yet clear and further investigations are needed. In conclusion, the obtained results can give an overview of the poroelastic behavior of the spinal cord. The findings of the influence of material properties can be useful for the research prosecution and the presented model can be improved to investigate other elements.