Surgery for Syringomyelia

Two forms of surgical intervention exist for syringomyelia: shunts, and decompression.

The following explanation is taken from Dr Clare Rusbridge's Syringomyelia Made Simple, a basic information document that has since been replaced with a more detailed document, Canine Chiari-like Malformation and Syringomyelia. The latter is excerpted below as well but the first extract is a good simpler introductory explanation of options:

Surgical management
Surgical management is indicated for dogs with significant pain or with worsening neurological signs. The aim is to restore CSF dynamics and if this can be achieved then the syrinx can resolve.  The most common procedure for Chiari like malformation is suboccipital decompression where the hypoplastic occipital bone and sometimes the cranial dorsal laminae of the atlas are removed (with or without a durotomy) to decompress the foramen magnum. The success reported in the small case series varies from no improvement to post operative resolution of the syrinx. Syringo-subarachnoid shunting has also been described.  In the author's experience surgery is usually successful at significantly reducing the pain but some dogs may still show signs of discomfort /scratching.  Also in the author's experience signs may recur in a proportion of dogs after several months/years.
One must weigh the risks and benefits of surgery versus medication versus no intervention.  Remember, progressive disease means that no action may enable further deterioration.
When to have surgery? 
There is more chance of success if the surgery is done early in the course of the disease before permanent damage has occurred. Surgical management is indicated for dogs with significant pain or with worsening neurological signs.
What are the risks of surgery?
There are major blood vessels in the area and if traumatised the dog could quickly bleed to death. Although not actually operating on the brain/spinal cord, it is in close proximity and there is a risk of permanent neurological injury. In reality complications from surgery seem to be rare.
Can the disease recur?
In the author's experience signs may recur in a proportion of dogs after several months/years due to redevelopment of syringomyelia. The newly created 'space' from surgery may fill in with scar tissue.  If this happens, repeat surgery may be indicated; some owner prefer to continue with medical management e.g. with frusemide, NSAIDs, gabapentin or corticosteroids.
What post surgery drug treatment would you advise? 
Dogs are hospitalised until comfortable enough for morphine-like-drugs to be discontinued and then discharged on a combination of non steroidal anti-inflammatory drugs (e.g. Rimadyl) and gabapentin (Neurontin). This is withdrawn when the dog is comfortable (about 2 weeks in most cases).

This is Dr Rusbridge's explanation of surgical options in her newer document, Canine Chiari-like Malformation and Syringomyelia:

The main treatment objective is pain relief. The most common surgical management is cranial/cervical decompression (also described as foramen magnum or suboccipital decompression) establishing a CSF pathway via the removal of part of the supraoccipital bone and dorsal arch of C1. This may be combined with a durotomy (incision of the dura with/without incision of subarachnoid meninges) with or without patching with a suitable graft material. Cranial/cervical decompression surgery is successful in reducing pain and improving neurological deficits in approximately 80% of cases and approximately 45% of cases may still have a satisfactory quality of life 2 years postoperatively (Rusbridge 2007). However surgery may not adequately address the factors leading to SM and the syrinx appears persistent in many cases (Rusbridge 2007). The clinical improvement is probably attributable to improvement in CSF flow through the foramen magnum. In some cases scaring and fibrous tissue adhesions over the foramen magnum seem to result in re-obstruction and 25% to as many as 50% of cases can eventually deteriorate (Dewey et al 2005, Rusbridge 2007). This can be as early as 2 months postoperatively. Recently, a cranioplasty procedure used in human cranial/cervical decompression surgery has been adapted for use in dogs. The procedure entails placement of a plate constructed of titanium mesh and polymethylmethacrylate (PMMA) on pre-placed titanium screws bordering the occipital bone defect (Dewey et al 2006). An alternative method of managing SM is direct shunting of the cavity. In humans this is not a preferred technique as long term outcome is poor due to shunt obstruction and/or spinal cord tethering. There has been a single report of syringo-subarachnoid shunting in a dog using an equine ocular lavage tube. However post-operative MRI revealed that SM was still prominent although there was a clinical improvement in the dog (Skerritt and Hughes 1998).

Due to the persistence of SM and/or spinal cord dorsal horn damage it is likely that the post-operative patient will also require continuing medical management for pain relief and in some patients medical management alone is chosen because of financial reasons or owner preference. There are three main drugs used for treatment of CM/SM: drugs that reduce CSF production; analgesics; and corticosteroids (Fig 3). If the dog’s history suggests postural pain or discomfort relating to obstruction of CSF flow then a trial of a drug which reducing CSF pressure, e.g. furosemide, cimetidine or omeprazole, is appropriate. This can also be very useful if it is difficult to determine if the cause of discomfort is CM versus, for example, ear disease. CSF pressure reducing drugs may be sufficient to control signs in some dogs, but additional analgesics are likely to be necessary for an individual with a wide syrinx. In this circumstance we suggest that non steroidal anti-inflammatory drugs are the medication of first choice partly because there are several licensed products. However, for dogs with signs of neuropathic pain, i.e. allodynia and scratching behaviour (suspected dysesthesia); a drug which is active in the spinal cord dorsal horn is more likely to be effective. Because gabapentin has established use in veterinary medicine we suggest that this is the drug of first choice but amitriptyline or pregabalin may also be suitable. Corticosteroids are an option if pain persists or where available finances prohibit the use of other drugs. Because the mechanisms of development of neuropathic pain are multifactorial, appropriate polypharmacy is likely to be more effective than treatment with single agents. Anecdotally, acupuncture and ultrasonic treatments have been reported to be useful adjunctive therapy in some cases. The dog’sactivity need not to be restricted but owner should understand that dog may avoid some activities and grooming may not be tolerated. Simple actions, for example raising the food bowl and removing neck collars, can also help.

Prognosis for CM/SM managed medically is guarded especially for dogs with a wide syrinx and/or with first clinical signs before 4 years of age. Study of a small case series (14 CKCS) managed conservatively for neuropathic pain suggested that 36% were eventually euthanatized as a consequence of uncontrolled pain. However 43% of the group survived to be greater than 9 years of age (average life expectancy for a CKCS is 10.7 years). Most dogs retain the ability to walk although some may be significantly tetraparetic and ataxic.