Outcome After Surgery
Outcome studies are conflicting and have many variables. The following is a brief overview of the most relevant concepts:
- Dependent on treatment type as driven by etiology: It is generally accepted that if the causative condition is identified and treated, the long-term potential for improvement and resolution of the syrinx is good (38). Prognosis is largely dependent on the prognosis of the primary pathological process that caused the syrinx.
- Chiari treatment treats syrinx: A syrinx in patients with Chiari I malformation generally responds well to posterior fossa decompression. In the largest series to date of 285 patients who underwent posterior fossa decompression for Chiari I malformation and syringomyelia, only four (1.4%) had postoperative progression of the syrinx that required additional surgery (54). It is notable, however, that this series is from a center with world-renowned expertise in the area. The rate of surgical failure likely is higher at centers with less experience.
- Spina bifida aperta symptoms respond: In patients with spina bifida, symptoms must be separated into those related to the syrinx, the tethered cord, shunt malfunction, or, less commonly, the Chiari II malformation. The results are usually good when the etiology is found (13). The literature on treatment failures is scant.
- Recurrence unusual after tethered cord release: In patients with congenital tethered cord (spina bifida occulta), earlier reports suggested that terminal syringomyelia, when large, requires syrinx drainage in addition to tethered cord release (11). However, the recent literature provides evidence that terminal syringomyelia, regardless of size, usually improves or resolves after tethered cord release, obviating the need for direct syrinx drainage or shunting (55).
- High recurrence when due to diffuse arachnoiditis: In patients with arachnoiditis, stabilization or reduction in the syrinx size can be achieved with decompression and arachnoid dissection in 83% of patients with focal scarring, but in only 17% of patients with scarring over multiple levels (12). Syrinx shunting alone results in very high recurrence rates.
- High failure rate expected for posttraumatic syrinxes: In patients with posttraumatic syringomyelia, outcome is largely dependent on pathology. If pain is secondary to ex-vacuo cavitation and the spinal cord injury itself, it is not surprising that it does not resolve with shunting of the cavity. Long-term recurrence rates with shunting alone have been in excess of 80% (12). When considering surgical treatment, it should be noted that patients for whom previous surgery has failed may have even worse outcomes.
- Outcome for tumor-associated syrinxes dependent on tumor: Patients with tumor-related syringomyelia generally have good outcomes with tumor resection, providing that the tumor itself is curable. It appears that preoperative neurological status is the main factor determining neurological outcome (34). For example, in their review of 44 patients with von Hippel-Lindau syndrome and spinal hemangioblastomas, Lonser et al. showed that the syrinx resolved in all patients after tumor removal, regardless of whether or not the syrinx cavity was entered (56).