Subarachnoid-Subarachnoid Bypass

A new type of surgical technique for posttraumatic syringomyelia has been described in the literature, subarachnoid-subarachnoid bypass (S-S Bypass). Hayashi et al. (2013) hypothesized that reconstruction of the subarachnoid channels could re-establish CSF flow and therefore correct the underlying issue causing syrinx formation. In general, the S-S Bypass technique is accomplished by surgical laminectomy at the level of trauma, followed by a midline dural opening made under a microscope. One or two silicone tubes are inserted into the cephalic and caudal ends of the normal subarachnoid space; after a watertight dural closure, Bypass tubes are laid in the subdural space (Hayashi 2013).

Author Year; Country
Research Design
Total Sample Size

Methods Outcome

Hayashi et al. 2013; Japan

Population: Mean age: 47.3 yr; Gender: males=19, females=1; Level of injury: thoracic=11, lumbar=5, cervical=4; Level of severity: complete=11, incomplete=9.
Intervention: All patients underwent a laminectomy at the level of trauma with ventricular drainage tubes inserted into the cephalic and caudal ends of the subarachnoid space. Bypass tubes were also inserted into the subdural space.
Outcome Measures: Frankel Score (neurologic status), AISA motor score, Klekamp system (bladder function), Syrinx length.

  1. Overall, 12 patients demonstrated clinical improvement, four remained stable and four showed deterioration of symptoms. Of the four who reported worsening symptoms, two improved after additional shunting but one reported no change.
  2. There was a significant reduction in mean syrinx length from pre-surgery to post-surgery (p<.01).
  3. A significant correlation was found between clinical outcome and change in the syrinx size whereby those who syrinx was reduced experienced clinical improvement (p=.01).
  4. No significant correlation was found between preoperative and postoperative scores for either the ASIA Motor Score (59.6 versus 60.8 respectively) or Klekamp system for bladder function (1.1 versus 1.0 respectively).


A single pre-post study has assessed the effectiveness of S-S Bypass in 20 individuals (mean age=47.3 years, 19 males) with SCI-related syringomyelia (Hayashi et al. 2013). The mean time since SCI was 126 months (range 2-336 months) and they were followed up, on average, for 48.2 months (range 12-93 months). Post-surgery, 12 patients showed improvements, four remained stable, and four showed signs of deterioration. Three of the four patients who demonstrated deterioration underwent a shunt replacement; two improved and one remained unchanged. There was no significant correlation between ASIA scores at baseline and follow-up. Finally, no patient experienced a CSF leak that needed treatment (Hayashi et al. 2013). The authors conclude that S-S Bypass is not only an effective method in treating syringomyelia but that it may be associated with better clinical results than those of other surgical interventions (e.g., shunts, cordectomy). Hayashi et al. (2013) state that S-S Bypass can be conducted without myelotomy therefore reducing the risk of neurological damage and does not usually require performing arachnoid lysis which avoids the possibility of scarring. Although there is a risk of re-scarring or re-tethering, the bypass tubes prevent the obstruction of CSF flow caused by re-scarring (Hayashi et al. 2013). However, a potential methodological concern of this study was the use of a subjective grading approach to patient improvement, stabilization and deterioration. Further investigation from multiple studies is required to make conclusions as to its clinical effectiveness.


There is level 4 evidence (from one pre-post study: Hayashi et al. 2013) that subarachnoid-subarachnoid bypass may improve motor and bladder functioning post SCI-related syringomyelia.