Spinal Tumour Surgery

Skeletal metastasis is discovered at the time of death in 60% - 70% of patients with malignant tumours out of which 40% – 50% affect the spine ⁽¹³⁾. Skeletal metastasis is the third commonest site of metastasis ⁽¹²⁾. The spinal column is the most common site of skeletal metastases ⁽³⁾. The majority of spinal secondaries come from primary cancers in the lungs, prostate, breast, kidney, thyroid and gastrointestinal tract. The cervical spine is usually involved in 10% of the metastasis while the lumbar spine is affected in 20%, and the thoracic spine is involved in the majority of the cases to the extent of 70% ⁽⁵⁾. Primary tumours of the spine form less than 2% of all spinal tumours, however, chordoma and osteoblastoma predominantly occur in the spinal column.

Surgical treatment in spinal tumours should aim at reducing pain, relieve compression of the neural elements, stabilise the spine mechanically, and achieve local control of the tumour. Enneking's oncological principles of surgical margins for long bone tumours may not entirely apply for spine tumours because of complex paraspinal visceral and vascular anatomy and lack of reliable instrumentation for complex spine reconstruction. However, with improvement in techniques and technologies en bloc resection has become possible with removal of single or upto three vertebral bodies in spine tumours.
In this article, we will discuss the different factors to be considered during surgery and its indications, followed by the different methods available for reconstruction in special situations.

1. En bloc resection/Curative resection
This can be performed in aggressive benign primary tumours, primary malignant tumours and solitary spinal bony metastasis with “bony-only” metastases from different primary solid tumours from viscera with good prognosis. Local malignancies like chordomas, selected sarcomas like chondrosarcomas, pancoast tumours, osteoblastomas and giant cell tumours respond well with en bloc resection. If the margins are tumour-free radiotherapy may not be needed after en bloc resection. However in some sarcomas where the dura that is adhered to the tumour must be excised, a watertight duroplasty with autologous fascia with or without appropriate muscle flap coverage must be performed. The muscle flap coverage is recommended if radiotherapy is considered.

To perform an en bloc resection of the spinal tumour a detailed surgical planning is required. The Weinstein-Boriani-Biagini system of spine tumour staging described in 1977 offers a simple and standardized way to plan en bloc vertebrectomy. In this system, the transverse extent of the tumour is described with references to 12 radiating zones (as like the face of the clock), and the longitudinal extent is described into five concentric levels from outside to inside upto the level of the dura and spinal cord/neural elements ⁽¹⁾

If the tumour involves either only the vertebral body or only the posterior elements, then both pedicles are cut to achieve the en bloc resection If the tumour occupies one side of the vertebral body and the ipsilatereal pedicle and articular process, a sagittal split osteotomy is performed to achieve en bloc resection. However, if the tumour involves both pedicles, surgery is aimed at minimizing the surface area of the tumour in which case it becomes an intralesional dissection.

2. Spinal Instability
Surgery may also be performed for spinal instability produced by tumours which can be categorized as acute or chronic. Spinal instability is the degree of motion beyond which pain, neurological deficit or abnormal angulation occurs ⁽⁹⁾. Spinal instability caused by tumours is different from that caused by trauma. Acute instability involves the presence of kyphotic deformity and/or subluxation with spinal cord compression accompanied by pain and/or myelopathy. This usually needs surgical stabilisation. Chronic instability involves compression fractures of various degrees and are usually subtle and usually not associated with spinal cord compression or severe pain. This can usually be managed by non-operative measures, however, when it progresses to acute form, may need surgical stabilisation.

Case 1 -Preoperative radiograph showing collapsed vertebral body due to metastasis

Case 1 -T2 weighted MRI Mid-sagittal scans revealing the tumour in the vertebral body

Case 1-Postoperative radiograph revealing anterior reconstruction with PMMA and Steinmann pins supplemented by Posterior pedicle screw instrumentation

3. Fusion or no fusion
Unlike in degenerative spines, fusion is not always the goal in spine tumour surgery. Pseudoarthrosis is defined as failure of attempted fusion one year after surgery. Many patients with spinal metastasis may not live long to assess fusion. However, it is still an issue in primary malignant spinal tumours and long-term survivors It has been shown in the literature that the rate of pseudoarthrosis increases with lumbar lesions, primary tumours or patients who received a radiation of more than 4000 rads postsurgery.

Spinal Reconstruction Surgery
There are essentially two approaches for reconstructing the spine after tumour excision.

a. Anterior reconstruction
In spinal tumours traditionally after spondylectomy, the gap is filled with methyl methacrylate (MMA). It has its advantages, viz, cheap, easily available, and resistant to tumour invasion and radiotherapy. A variety of grafts, both auto- and allografts are also used for this purpose, however, fusion is a concern especially if postoperative radiotherapy is employed. For patients with more than 6 months of life expectancy, allografts or cage may be used. Stackable carbon fibre or titanium cages are frequently used in anterior reconstruction. During the last few years several artificial materials and implants have been developed to replace the vertebral body and include titanium cages, ceramic, ceramic/glass, and carbon fibre spacers.

b. Posterior instrumentation
This is often accomplished by screw (pedicles and lateral masses) and this is preferable than hooks in spinal reconstruction for tumours. The posterior constructs are under high stress at the proximal and distal end of the spine especially if it is associated with kyphotic deformity. Reduction of the deformity in such cases may be obtained by using cross-rod bending technique. Wires and hooks through either the kyphotic or lordotic deformity should be avoided. Posterior constructs can be used to reduce kyphosis by placing it in compression or to produce kyphosis by placing it in distraction. Care should be taken not to end the level of the construct in segments where there is tumour involvement, junctional zones (cervicothoracic, thoracolumbar), spondylolisthesis, spinal stenosis or significant degenerative changes.

c. Anterior or Posterior reconstruction
When considering spinal reconstruction in spinal tumours, failure has been reported in anterior or posterior reconstruction alone. Hence, a combined approach with both anterior and posterior or a staged approach with posterior fixation after an anterior reconstruction is used in most cases. Oda et al demonstrated superior fixation biomechanically with a combined anterior-posterior reconstruction than an anterior or a posterior reconstruction alone in thoracolumbar total vertebrectomy ⁽⁷⁾.

Special Considerations

Cervical Spine Reconstruction
As most of the metastatic lesions involve the vertebral body, anterior cervical corpectomy followed by reconstruction and stabilisation is an effective way of surgical management in most cases. PMMA assisted reconstruction is useful in patients with limited life expectancy. Dislodgement of the PMMA used to be a problem, however recent techniques of using Steinman pins and filling the resection cavity with PMMA ⁽¹¹⁾, and using various rod and hook systems seems to overcome the problem. To prevent the dura getting affected by the exothermic reaction, a gel foam or a fat pad may be used. In conjunction with PMMA to augment the fixation some authors ⁽⁸⁾ have described the use of a ceramic prosthesis. Further, the construct failure can also be reduced by the addition of anterior cervical locking plate and screws ^{(2, 6)}. Coaxial double-lumen PMMA reconstruction using the chest tubes have been described that yield excellent clinical results especially when combined with anterior plating and/or posterior instrumentation ⁽⁶⁾. To fill the vertebrectomy defect, a titanium mesh cage can be used as a cylindrical interbody reconstruction device that can be filled with auto- or allograft or even PMMA. A titanium Telescopic Plate Spacer (TPS) can be used as a hybrid interbody spacer to reconstruct either one- or two-level corpectomy defects and simultaneously achieve maximum kyphosis correction ⁽⁴⁾. The TPS provides immediate stability allowing early mobilization without the need for external orthosis.

Case 2-Post-percutaneous vertebroplasty

Case 2-Preoperative radiograph showing collapse of vertebral body

Case 2 -n Sagittal CT scan showing the involved vertebral body

Cervicothoracic Spine Reconstruction
Similar to the cervical spine reconstruction, anterior column reconstruction can be performed with PMMA cast held by vertical Steinmann pins or use of fibular allograft or iliac crest autograft or a mesh cage packed with autograft. Further, anterior cervical plates, Harms cage, expandable cages and metal spacers come into help for anterior reconstruction. Posterior reconstruction can be performed with iliac crest autograft and/or local autograft from laminectomy along with various posterior instrumentation like interspinous or facet wires, Luque rods and sublaminar wires, paediatric Cotrel-Dubousset hooks and rods, AO plates and lateral mass screws, pedicle screws, polyaxial screws, dual-diameter rods and interlocking connections.

Significant anatomical variations are common as the cervicothoracic junction represents a transition zone and also a change from a mobile cervical lordosis to a rigid thoracic kyphosis. Further, the lower cervical laminae are thinner and weaker compared ti the upper thoracic vertebrae. Additionally as the spinal canal at this level is narrow, this may limit the use of the hook/rod system for cervicothoracic spine stabilisation. While using lateral mass screws care should be taken to avoid vertebral artery and spinal nerves.As the cervicothoracic junction represent an area of inherent instability, it is advisable to produce a long construct for spinal stabilisation, by including at least three or four levels above and below the diseased area.

Percutaneous vertebroplasty
This is a newer technique where the collapsed vertebral body in myeloma (as in osteoporosis), is injected with acrylic cement using a needle to stabilise the painful compression vertebral fracture. It is believed that pain relief in such cases is obtained by mechanical support and stability provided by the bone cement to the vertebral body. Complication rate is 1%-3% when treating for osteoporotic vertebral fractures, while it is 7%-10% when treating malignant vertebral fractures. This technique stabilises and strengthens the vertebral body but does not restore the height or shape of the vertebral body.

Is surgical treatment better than radiotherapy alone in spinal metastases?
Patchell et al in their multicentre prospective randomized controlled trial comparing the efficacy of surgery to radiotherapy in patients with vertebral body metastatic disease and neurological deficit found that surgery followed by radiotherapy than radiotherapy alone produced superior outcome with significantly higher number of patients with surgery regaining their ability to walk and tended to maintain their newfound mobility longer than the nonoperative group. Further the need for corticosteroids and analgesics were decreased in the surgical group. Additionally, there was improvement in maintenance of urinary incontinence, muscle strength and neurological profile as determined by ASIA scores, improvement in functional ability as determined by Frankel grading and also survival time in the surgical group compared to the non-operative group with radiotherapy alone.

Conclusion
Surgical treatment plays an important role in the management of spinal tumours and continues to expand and improve as the population with spinal tumours also is growing in numbers with longer life expectancy. Instrument technology and biological innovations continue to improve, however stringent biomechanical testing and clinical studies are necessary to affirm their effectiveness before we apply in our clinical practice.

References

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10. Patchell RA, Tibbs PA, Regine WF, et al. Direct decompressive surgical resection in the treatment of spinal cord compression caused by metastatic cancer: A randomised trial. Lancet 366:643- 648, 2005
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