Hypothesis on the pathophysiology of syringomyelia based on analysis of phase-contrast magnetic resonance imaging of Chiari-I malformation patients

Background: Despite a number of hypotheses, our understanding of the pathophysiology of syringomyelia is still limited. The current prevailing hypothesis assumes that the piston-like movement of the cerebellar tonsils drives the cerebrospinal fluid (CSF) into the syrinx through the spinal perivascular space. However, it still needs to be verified by further experimental data. A major unexplained problem is how CSF enters and remains in the syrinx that has a higher pressure than the subarachnoid space. Methods: I analyzed phase-contrast MRI scans of 18 patients with Chiari-I malformation with syringomyelia undergoing foramen magnum decompression and 21 healthy volunteers. I analyzed the velocity waveforms of the CSF and the brain in various locations. The obtained velocity waveforms were post-processed using a technique called synchronization in situ. I compared between the preoperative data and the control data (case-control study), as well as between the preoperative and postoperative data (cohort study). Results: The syrinx shrank in 17 (94%) patients with good clinical improvement. In Chiari-I patients, the velocity of the tonsil was significantly larger than controls, but was significantly smaller than that of the CSF in the subarachnoid space, suggesting passive rather than active movement. The abnormal tonsillar movement disappeared after surgery, but the velocity waveform of the spinal subarachnoid CSF did not change. These results, contradicting the above mentioned hypothesis, required an alternative explanation. I thus hypothesized that there is a CSF channel between the fourth ventricle and the syrinx. This channel assumes one-way valve function when mildly compressed by the cyclical movement of the cerebellar tonsil. The decompression of the tonsils switches off the one-way valve, collapsing the syrinx. Conclusions: My hypothesis reasonably explained my data that clearly contradicted the existing hypothesis, and successfully addressed the above-mentioned theoretical problem. It will serve as a working hypothesis for further study of syringomyelia pathophysiology.