There are, broadly speaking, three types of surgical manoeuvre that we can offer to a patient with syringomyelia (Table 11.3). Clearly, it makes sense to treat the underlying cause if possible. So, when we can identify a focal point of obstruction to CSF movement, the logical approach is to try and relieve that blockage and create a new conduit for CSF flow. This is, of course, a major operation, involving the removal of several laminae, and it requires microsurgical technique for the intradural part of the procedure. In most cases of post-traumatic syringomyelia, the scar tissue encountered is relatively limited in extent, and breaking it down is not unduly difficult. The offending cicatrix is clearly recognisable by its typical milky-white appearance and can be readily distinguished from normal, translucent arachnoid. Dissection dorsal and dorsolateral to the cord will eventually result in it falling anteriorly, into the spinal canal. At this point, the syrinx has usually collapsed and the cord may begin to pulsate. It is unnecessarily hazardous for the dissection to be carried anteriorly, although opinions vary as to the value of dividing dentate ligaments . The exposure also needs to be of sufficient length to allow free, rhythmic movement of CSF, up and down the spinal canal.

The anatomical results from this sort of surgery can be very satisfying (Fig. 11.4). The problem is that blood products and muscle proteins, which are inevitably “spilt” into the laminectomy site, may go on to organise into scar tissue once more, and this leads to recurrent obstruction of the spinal subarachnoid channels (Fig. 11.5). Early postoperative imaging is, therefore, of limited value; it is very likely to show a reduction in the volume of the syrinx, but this by no means guarantees long-term anatomical improvement. If, however, the cavity remains collapsed at 6 months and beyond, then it is likely that a good result will have been achieved in the long term, in anatomical terms at least and probably in terms of function as well.

How the dura is handled is likely to have a major influence on the success or otherwise of this operation. With craniovertebral decompression for hindbrain-related syringomyelia, we have discussions about dural opening – full, partial or not at all – reduction or excision of cerebellar tonsils, use of dural grafts and the role of cranioplasty. We have similar debates about the best methods of exposure and closure, when it comes to operating for post-arachnoiditic syringomyelia. Dural patch grafts might be expected to limit the amount of blood and muscle products entering the spinal theca, from the surrounding tissue planes. This, we might expect, would lessen the amount of postoperative scar tissue formation. Many surgeons therefore feel more comfortable reconstituting the thecal sac, usually augmenting its volume at the same time by suturing in place a patch graft. Autografts are readily obtained from nearby muscle fascia, but synthetic materials are now preferred by most surgeons, mainly because they provoke less in the way of postoperative adhesions. The risk, however, with any form of patch graft, is that CSF may leak around its edges and collect extradurally. This may lead to a build-up of hydrostatic pressure, which pushes the graft onto the cord. This can encourage adhesions to develop between the graft and the cord. This constricting effect becomes more pronounced as healing progresses and defeats the object of opening up CSF channels in the first place. The resultant obstruction to CSF flow may be worse than preoperatively, leading to refilling of the syrinx. Many surgeons therefore make a point of hitching the dural patch graft upwards, to try to prevent such adhesions forming. The author’s preference has been to leave the dura widely open, using lateral retaining sutures. With a good closure of the long paraspinal muscles, a pseudomeningocoele forms between the short muscles and this provides a conduit for CSF flow. It is important to pay close attention to the cranial and caudal aspects of the thecal opening, taking care to suture up the dura under the laminae at the upper and lower aspects of the exposure, to ensure that adhesions do not form at these sites. Leaving the dura open also provides an opportunity for placement of temporary subdural stents or drains (Williams and Page 1987). A soft drainage tube, left in place for no more than 48 h, not only serves as a stent but also allows CSF to “auto-irrigate” the subarachnoid channels and drain blood products away (Fig. 11.6). One study did note, however, a higher syrinx recurrence rate if the dura was left open in this way, although the difference between the two groups did not reach statistical significance (Klekamp et al. 1997).

If the attempt to create a conduit fails, or is not suitable for some other reason, then the option of draining the syrinx is available. Indeed, this was a principal means of treatment for some years, and results were considered to be reasonable (Tator et al. 1982; Williams and Page 1987). About half of the patients treated by direct drainage of the syrinx will obtain useful relief (Batzdorf et al. 1998; Sgouros and Williams 1995). The method, however, has a number of drawbacks. In the first place, a myelotomy is required, with an incision through the dorsal columns. Some loss of proprioception is almost inevitable, and this is often more disabling for patients than one might expect, despite the individual retaining good motor power. Further, septa within larger syrinx cavities may obstruct passage of the shunt tubing. The concern then is that the cavity will not drain adequately although, in truth, this is not always a problem. The main difficulty with syrinx drainage tubes is that, in common with all shunt systems, there is a distinct likelihood that they will eventually block. Even if a shunt continues to function and the syrinx remains collapsed, there is a chance that a new cavity may form alongside, simply because the underlying filling mechanism has not been disabled (Fig. 11.7).