Introduction: Enlarging cystic cavitations (syrinxes) form within the spinal cord in up to 28% of spinal cord injured patients. These post-traumatic syrinxes can cause neurological deterioration, and treatment results remain poor. Syrinxes are often found adjacent to regions of arachnoiditis.

The understanding of biological systems is increasingly dependent on modelling and simulations. Numerical simulation is not intended to replace in vivo experimental studies, but to enhance the understanding of biological systems. This study tests the hypothesis that pressure pulses in the SAS are high adjacent to areas of arachnoiditis and investigates the validity of a numerical model by comparison with in vivo experimental findings.

Methods: Experimental Model: Post-traumatic syringomyelia was induced in eight sheep by injection of kaolin into the subarachnoid space (SAS), and excitotoxic amino acid into the spinal cord of the upper thoracic spine. Cerebrospinal fluid (CSF) pressure studies were undertaken at either 3 or 6 weeks. Fibre-optic monitors were used to measure the pressure in the SAS 1 cm rostral and 1 cm caudal to the induced arachnoiditis.

Numerical Model: An axisymmetric fluid-structure interaction model was developed to represent the spinal cord and SAS under normal physiological conditions and in the presence of arachnoiditis. Arachnoiditis was modeled as a porous obstruction in the SAS.

Results: In both models the SAS pressure rostral to the arachnoiditis was found to be higher than the caudal SAS pressure. There was no statistically significant difference between the sheep at 3 and 6 weeks. Under normal conditions, both experimentally and in the numerical model, the pressure drop along the SAS was negligible. In the presence of arachnoiditis, the pressure drop across the arachnoiditis in the experimental model was 1.6 mmHg, whereas the numerical model predicted a pressure difference of 1.3 mmHg.

Discussion: The numerical model accurately predicts CSF pressures in the animal model under both normal and abnormal conditions, allowing predictions to be made to within 20% accuracy. The local increases in SAS CSF pressure demonstrated may act to increase fluid flow through perivascular spaces and be implicated in syrinx formation and enlargement.