Pathogenetic role of myelitis for syringomyelia

Background: CSF-flow obstruction is regarded as a mandatory factor for the development of syringomyelia. However, there are conditions in which syringomyelia is not associated with evident persistent CSF-flow obstruction, as in the case of inflammatory spinal cord lesions. In these instances we hypothesize that the accumulation of vasogenic edema may play a role in the development of the syrinx. Recently proposed theories underline, even in the event of CSF-flow obstructions, a major role for the accumulation and final coalescence of interstitial spinal fluid, rather than CSF penetration through the spinal cord. Aim: To clarify the relationship between syrinx development and spinal cord inflammation, through the analysis of the role of intrinsic medullary factors versus CSF-flow block. Methods: A prospective case series including patients with transient syringomyelia associated with different examples of non-infectious myelitis: sarcoidosis, post-infectious transverse myelitis, Devic's disease and multiple sclerosis. Cavitations resulting from cystic myelomalacia were excluded. CSF-flow block was assessed by structural MRI. Results: Syringes associated with myelitis shared some common features: they developed during the acute phase of myelitis and disappeared after steroids, were all non-communicating cavitations involving the central canal, and occurred in the same spinal segment affected by myelitis. CSF-flow obstruction was detected in one patient (Chiari I malformation), while in the other three patients we could not detect anatomical predispositions. Conclusion: Only one patient had structural abnormalities, though without evidence of a pathogenetic role in itself: however, CSF space obstruction and reduced CSF compliance could have accelerated the development of syringomyelia triggered by intramedullary inflammation. The clinical and radiological features in this patient are consistent with the label "presyringomyelia". The absence of any anatomical predisposition in the other patients suggests a major pathophysiological role for intrinsic medullary mechanisms, including blood-spinal cord barrier breakdown, impairment of extracellular fluid drainage, and leakage of subarachnoidal CSF into the nervous tissue.