Direction-selective Resistance to Cerebrospinal Fluid Flow as the Cause of Syringomyelia

The pathophysiology of syringomyelia remains poorly understood. Two prevailing challenges stand out: the need for a comprehensive understanding of its diverse types and the yet-to-be-explained mechanism of cerebrospinal fluid (CSF) retention in the syrinx despite its higher pressure than that in the adjacent subarachnoid space. Expanding on our previous proposal that direction-selective resistance to subarachnoid CSF flow drives syringomyelia genesis, this study uses a computer model to explore this mechanism further. We developed a computer simulation model to study spinal CSF dynamics, employing a lumped parameter approach with multiple compartments. This model replicated the to-and-fro movement of CSF in the spinal subarachnoid space and within an intraspinal channel. Subsequently, a direction-selective resistance-opposing only the caudal subarachnoid CSF flow-was introduced at a specific location within the subarachnoid space. Following the introduction of the direction-selective resistance, a consistent pressure increase was observed in the intraspinal channel downstream of the resistance. Importantly, this increase in pressure accumulated with every cycle of to-and-fro CSF flow. The accumulation results from the pressure drop across the resistance, and its effect on the spinal cord matrix creates a pumping action in the intraspinal channel. Our findings elucidate the mechanisms underlying our hypothesis that a direction-selective resistance to subarachnoid CSF flow causes syringomyelia. This comprehensively explains the various types of syringomyelia and resolves the puzzle of CSF retention in the syrinx despite a pressure gradient.