Syringomyelia and Tethered Spinal Cord
Subsequent to a traumatic SCI, the overarching goal is preservation of residual neurological function and, to the extent possible, reacquisition of previous function. One longer-term pathological process that can interfere with this a spectrum of changes termed spinal cord tethering and post-traumatic syringomyelia.
Over the long term, some scar tissue associates with the injured spinal cord and causes pathological adhesion or tethering to the surrounding dura. This can result in undue traction being placed on the segment of spinal cord cranial to the injury, resulting in new, but delayed, progression of neurological deficit. Similarly, the injured cord can acquire localized atrophy and myelomalacia, resulting in intramedullary cystic cavitation, with the cyst filling with cerebrospinal fluid. If this fluid compartment, or syrinx, develops mass effect, then this can similarly present with delayed worsening of neurological deficit. Both of these processes can have a devastating impact on function depending on the level of injury-for example, an individual with a high thoracic injury can be at risk of losing their upper extremity function if a symptomatic tethered cord or syrinx develops. Because of the significance of this pathology, surgical treatment and/or preventative options have been considered.
Discussion
The largest case series is that of Falci et al. (2009a) who published both early and late follow-up results. They describe 362 individuals surgically treated for tethered cord and/or syringomyelia. Each had delayed neurological decline after traumatic cord injury, attributable to tethering and/or syrinx, and demonstrated statistically significant declines in AIS scores during the first year of assessment. After surgical detethering (and in 20% of individuals, syrinx shunting), AIS scores remained statistically stable over a variable follow-up period from 2 to 12 years. This suggests that in individuals with delayed deterioration, surgical intervention is capable of arresting neurological decline, but not necessarily restoring neurological function. The same individuals responded via questionnaires that their perceptions of spasticity, hyperhidrosis and neuropathic pain had improved post-operatively, but there was no comparator group.
A systematic review of post-traumatic syringomyelia management (Bonfield, Levi, Arnold, & Okonkwo, 2010b) found that the incidence of this process is 1-4% among spinal cord injured individuals, and is twice as prevalent in complete, compared to incomplete, injuries. Despite post-traumatic syrinx being more prevalent in individuals with residual kyphosis at the level of injury, their review of low and very low quality retrospective studies found no evidence to prophylactically decompress the injured segment during the index surgical treatment; that is, they advised to not change surgical strategy in hopes of syrinx prevention.
With regard to surgical indications for syrinx, the systematic review by Bonfield et al. (2010b) summarized retrospective studies and prospective cohort studies. The authors concluded that surgery was only recommended for progressive motor deterioration, and that progressive pain syndromes, sensory disturbance or other non-motor progression was not recommended. Bonfield et al. (2010a) also addressed different methods of syrinx decompression. These range from spinal cord transection, to cerebrospinal fluid shunting to either the subarachnoid or pleural space, pseudomeningocoele creation, to expansile duraplasty. In general, after review of the mostly retrospective literature, there is no clearly superior technique, although a consensus pointed towards cord detethering and expansile duraplasty.
Conclusion
There is level 3 evidence (from one prospective cohort: Falci et al. 2009b) that cord detethering with or without syrinx decompression can arrest neurological decline in individuals with delayed progressive myelopathy following SCI.
There is level 4 evidence (from one systematic review: Bonfield et al. 2010a) that prophylactic measures for cord tethering and/or syrinx should not be taken, other than what is required to achieve primary spinal realignment / stabilization during the index surgery.
