Downs Veterinary Referrals

Introduction

Following on from the last article in our Winter 2012 edition of Downs Diary – Assessment of the Spinal Patient – we thought it might be useful to outline the various treatment options for some of the more commonly encountered causes of spinal disease as even though you may not perform spinal surgery yourself, clients will often request such information at initial presentation. We also offer an update on current thinking for management of the more obscure spinal conditions.

Intervertebral Disc Disease

Intervertebral disc disease (IVDD) is the most common indication for surgical intervention of the spine.  Cases are managed according to their grade of injury, where the presence or absence of conscious pain perception (CPP) is critical to decision-making. However, other factors, including the general health status of the patient, finances, access to specialised diagnostic/surgical equipment, appropriate nursing facilities and the experience of the surgeon and support staff available will inevitably influence patient management.

Table 1, summarises the treatment  options for IVDD; those most commonly taken at Downs Veterinary Referrals are highlighted in green.

Conservative management

It should be emphasised in every case that strict compliance can mean the difference between a successful outcome and progression to irreversible neurological injury.  Cases with suspected IVDD should be confined to an area just large enough to accommodate a bed (at floor level) and feed bowls (plus litter tray where appropriate).  Animals should be supported when walked or carried out for toileting and steps or steep slopes should be avoided.  Once outside, animals should be kept on a short leash and returned to confinement as soon as toileting is complete.

Dorsal annular tears take a minimum of six weeks to repair, so increased activity levels before this point will increase the risk of recurrence or progression of signs.

Regular reassessment of these patients is essential as treatment options may need to be revised if there is evidence of progression or unmanageable pain.

Opiates, NSAID’s or anti-inflammatory doses of steroid and gabapentin may beconsidered for analgesia, but so called ‘high-dose’ steroid therapy is NOT indicated for spinal disease in animals; this merely increases the complication rate and does not improve the outcome.

Disc fenestration

Indicated for patients with suspected (mineralised discs seen on survey radiology) or confirmed, low grade IVDD.

The objectives for disc fenestration are twofold:

A) the removal of all degenerate nuclear material from within abnormal discs so as to prevent further extrusion into the neural canal and,

B) a reduction in the degree of dorsal annulus deformation where it compresses neural structures.

A) is met instantaneously – it is extremely rare for patients to show deterioration in neurological grade or recurrence of signs due to further extrusion in a particular disc following fenestration of that disc.

B)  may take several weeks to be met as it relies on healing of the annulus.  Owners should therefore be advised that deficits and spinal pain may persist for several weeks.  It is also important that activity is kept to a minimum during this time to aid healing.

fig. 1 - schematic diagram to illustrate mild, left-sided disc deformation secondary to degenerative changes in the nucleus pulposus. This may result in entrapment of the corresponding nerve root at that level.

fig. 2 - schematic diagram to illustrate left-lateral disc fenestration to remove the degenerate nucleus pulposus.

Thoracolumbar discs are usually fenestrated via a lateral approach (see figs. 1 & 2).  Several discs may be tackled at one time.  The discs to be fenestrated are selected on the basis of degenerative changes, such as deformation of the disc in transverse slices and loss of normal hydration of the nucleus, as assessed by T2W MRI sequences.  If MR-scans are unavailable, then fenestration of discs T11-L3 would tackle the majority of potential future extrusion sites.  However, this ‘blind’ approach does risk unnecessary surgical trauma and L4-7 extrusions are not unknown.

Cervical discs are fenestrated via a ventral approach.  Again, disc selection is based on deformation and the degree of hydration of the disc.

Fenestration of Hansen type II disc deformation is more controversial as some surgeons believe that this may de-stabilise the joint and predisposes to further disc deformation with the potential for increased compression of neural structures.  However, experience here lends us to believe that fenestrations are a realistic option in this group of patients.

The procedure can be performed with minimal surgical instrumentation, but clients should be warned as to specific complications which include worsening neurological grade, segmental neuropraxia, haemorrhage of major vessels, oesophageal trauma (in the case of cervical fenestrations) and pneumothorax.

Despite the above, the vast majority of patients that undergo disc fenestrations suffer remarkably little morbidity and recover rapidly, with very low rates of recurrence on long-term follow up.

Decompressive surgery

Compression of the spinal cord and associated nerve roots may be alleviated by one of two strategies:

fig. 4 - schematic diagram to illustrate left-sided hemilaminectomy facilitating direct relief of cord compression.

fig. 3 – schematic diagram to illustrate left-sided disc extrusion. There is significant compression of the spinal cord at this level.

(i) Direct decompression by way of the removal of bony structures entrapping the neural tissue (hemi-, dorsal-laminectomy, pediclectomy, corpectomy, ventral slot and intervertebral foramen techniques) to access and remove disc material and haematoma directly (see figs. 3 & 4).  This will reduce the risk of further injury to the spinal cord by improving vascular perfusion and resolving inflammation of nerve roots affected by the presence of degenerate disc material, haemorrhage and ruptured or deformed annulus.

(ii) Distraction and stabilisation techniques facilitate indirect decompression particularly where there is dynamic, rather than static compression (e.g. ‘wobblers’ and lumbosacral disease).  A number of different techniques have been tried over the years, but all involve inserting some form of implant to widen the intervertebral space.  This results in a flattening-out of the dorsal deformation of the annulus and widening of the intervertebral foramen to reduce impingement of nerve roots.  The major complications seen with this approach include implant-related disease and a ‘domino-effect’ where neighbouring discs develop degenerative changes due to a stress-riser effect.

Trauma

fig. 5 - lateral radiograph of one-year-old crossbred dog following RTA, showing fracture luxation at T12-13. Clinical assessment revealed no CPP caudal to the lesion and the patient was euthanased.

As with disc-related injury, the single most important prognostic indicator is the presence or absence of CPP; an extremely guarded/ grave prognosis should be offered with CPP-negative trauma cases, with the option of euthanasia considered at an early stage (see fig. 5).

Bio-mechanical factors which indicate surgical intervention include instability across the damaged area of the spinal column and the compression arising from the presence of bone fragments/ disc material within the neural canal or mal-alignment secondary to fracture/ luxations.

Assessment of stability

In general, damage to the dorsal third of the vertebrae (the neural arch along with its associated processes and articular facets) will not compromise stability enough to warrant surgical stabilisation.  The exception to this rule would be rupture of the dorsal, interarcuate, atlanto-axial ligament.

Fracture/ luxation of the vertebral bodies however, will usually require surgical intervention.  As with appendicular fractures involving a joint, surgical management should achieve anatomical reduction with rigid internal fixation.  A number of methods can be used, usually involving a combination of screws, plates, pins and bone cement.

External fixation can also be employed but requires fluoroscopy or an open approach for accurate reduction and pin placement.

Developmental Disease

A wide variety of conditions may be encountered which have a diverse range of presenting signs.  Early diagnosis with surgical intervention is often key to maximising the potential for recovery and so limit chronic morbidity.

fig. 6 - ventrodorsal post-operative radiograph of a four year old male, neutered Yorkshire terrier presenting with non-ambulatory tetraparesis, showing screw placement for stabilisation of atlantoaxial sub-luxation.

Atlantoaxial instability

Seen in juvenile or young adult toy-breeds as variable neck pain with or without deficits.  Diagnosis by means of radiology with cautious ventro-flexion of the cervical spine.  Treatment involves placement of screws across the synovial Ce1-2 joint (see fig 6).

Sub-arachnoid Cyst

These are often progressive and can present in juveniles and adults.  Treatment of choice for surgically accessible cysts is laminectomy/ marsupialisation, with a favourable prognosis in most cases.

fig. 7 - intraoperative view of foraminal decompression of a six year old male, neutered Cavalier King Charles Spaniel presenting with cervical spinal pain secondary to syringomyelia. The caudal portion of the cerebellum can be seen to extend caudally beyond the level of the foramen magnum

Syringomyelia

Again, age of onset is variable but signs are usually fist noted in the young adult.  These  are variable and range from incessant scratching to shifting lameness and spontaneous vocalisation.

Surgical intervention in the form of foramenotomy/ occipitoplasty will reduce reliance on medication (see fig. 7).  However, recurrence due to scarring may necessitate chronic medical therapy or repeat intervention.

Inflammatory Disease

Surgery is indicated where there is persistent or focal areas of infection, unresponsive to medical therapy.  Debridement with lavage +/- omentalisation will often resolve the underlying infection. Consideration should also be given to addressing any compression of neural structures as a result of chronically inflamed tissue, e.g. within nerve-root outflow tracts secondary to lumbosacral discospondylitis (see fig. 8).

fig. 8 - T2W sagittal slice of a seven-year-old female, neutered Boxer with lumbar spinal pain. There is increased signal intensity and poor margination of the lumbosacral disc with extension into the surrounding end-plates, consistent with discospondylitis.

Neoplasia

fig. 9 - STIR transverse slice of a 10-year-old female, neutered Lhasa Apso with left thoracic limb lameness. There is irregular enlargement of the left Ce7 nerve root consistent with malignant peripheral nerve sheath tumour.

The majority of spinal tumours are challenging to treat surgically as clear margins are often not attainable without unacceptable iatrogenic trauma to surrounding neural tissue.  Canine meningiomas usually behave in a malignant fashion, in contrast to feline ones, where curative surgery is a realistic goal.  Even malignant peripheral nerve sheath tumours (see fig.9) which appear to arise some distance from the spinal cord will usually have microscopic infiltrates along the proximal nerve sheath, limiting the role of surgery to palliation.  However, these tumours are usually slow-growing and medical management can often deliver an acceptable quality of life for several months following diagnosis.  Spinal lymphomas often respond extremely well to chemotherapy in the short-to-medium term.