A numerical investigation of waves propagating in the spinal cord and subarachnoid space in the presence of a syrinx

The term syringomyelia describes fluid-filled cavities in the spinal cord, which can interfere with normal nerve signal transmission. The finite-element code ADINA was used to construct an axisymmetric fluid/structure-interaction model of the tapered spinal cord and subarachnoid space (SAS), bounded by the dura mater. A syrinx was simulated, of corresponding dimensions to one shown by magnetic resonance imaging data of a patient with syringomyelia. The model was used to investigate the clinical hypothesis that SAS pressure waves move fluid along a syrinx and can thus lengthen it over time by tissue dissection. Simplified versions of the model were used to examine in detail the waves excited, and their reflection and refraction at sites of property discontinuity in the system. Comparison was made with wave predictions based on an analytical model, and excellent agreement was found. The results suggest that, under the circumstances modelled, pressure wave-induced motion of syrinx fluid is unlikely to lengthen such cavities, unless the transverse tensile strength of cord tissue is even smaller than has been appreciated so far.