The spine is the commonest site in the musculoskeletal system for the presentation of tumours. The vast majority of these will be metastatic in origin with the common primary sites being breast, prostate, thyroid, lung, kidney and the GI tract in that order. However there are also a small proportion of primary tumours both benign and malignant which are important to detect. Considering all primary malignant bone tumours, primary malignant spinal tumours only make up to about 2-5%, so the infrequency makes it a group of tumours often missed by non spinal healthcare professionals. Tumours of the spinal cord are generally treated by neurosurgeons and are outside the scope of this article.
For primary tumours of the spine, there are thought to be five attributes that a cell needs to acquire to become growth deregulated. These attributes also apply to non musculoskeletal tumours including the common primaries for skeletal metastases.
- Self sufficiency from growth factors
- Resistance to growth - inhibitory factors
- Resistance to apoptosis
- Immortalization (ability to endlessly proliferate)
- Sustained angiogenesis
Mutations in genes which regulate cellular proliferation confer these attributes and examples include protooncogenes and tumour suppressor genes.
Primary tumours originate from four cell lines, osteoblast, fibroblast, chondroblast and osteoclast.
- Tumours derived from osteoblast typically show active ossification and calcification eg osteoid osteoma, osteosarcoma.
- Those derived from the fibroblast line typically show collagen formation eg fibroma, fibrous histiocytoma.
- Chondroblast derived tumours show cartilage in their architecture eg osteochondroma, chondrosarcoma
- Osteoclast lineage tumours typically show bony destruction eg giant cell tumour.
Metastatic spread occurs according to the 'seed and soil' theory of Harrington. Tumour emboli seed the blood stream and then embed in natural filter regions such as the highly vascularised red marrow of vertebral bodies. The subchondral endplate causes arterioles to loop back on themselves similar to vessels in the metaphyseal region of long bones allowing the metastases to 'seed' here. Regionally, this can be further subdivided into thoracic spinal metastases which often come from breast and lung. Here, seeding of the spine occurs through the valveless paravertebral venous plexus as described by Batson. Lumbar metastases commonly originate from the prostate which drains through the pelvic plexus into local capillaries around the vertebral bodies by the way of Batson's lumbar plexus. Anatomically malignant tumours tend to present in the pedicle or vertebral body (exceptions: giant cell tumour and haemangioma) whilst the benign tumours commonly arise in the neural arch of the spine.
History & Examination
- The cardinal symptom is pain either local or radicular.
- The pain can be locally axial in the back or neck when the pain is often caused by tumour mass expanding vertebral body cortex
- The pain can be radicular if compression or invasion of a nerve root is involved. This is often a late manifestation of the tumour often preceded by a long history of axial pain
- Tumour pain often has a gradual onset and progressive
- Although it can be acute onset with pathological fracture
- It can be difficult to differentiate from a herniated disc or spondylosis but tumour pain doesn't usually improve with rest and is often worse at night waking the patient up
- Don't forget general systemic symptoms of malignancy eg weight loss etc
'Localized, progressive, unrelenting, nonmechanical, worse at night'
Age is worth bearing in mind as 80% of spine metastases occur in patients over 40yrs old and primary spine tumours in those aged over 21yrs tend to be malignant.
In terms of examination, there are two aspects:
- Spine (palpation and range of motion) and full neurological exam important as it correlates with post treatment outcomes
- Potential metastatic source (breast / prostate / lung / thyroid / kidney / GI tract)
Several investigations are used in the evaluation of tumours both for diagnostic and surgical staging purposes. There is no standardised protocol for imaging of tumours but discussion with your local radiology department is required.
- AP and lateral views give indirect evidence of mass lesions
- Bony trabecular destruction not apparent until 30-50% destroyed. 1cm cortical bone or 1.5cm trabecular bone needs to be destroyed before plain films will demonstrate it
- If lesions identified - location within vertebra / appearance (lytic/blastic/mixed) / pattern of bony destruction. Prostatic metastases tend to be sclerotic
- Insensitive at detection of metastases
- Winking 'owl' sign (loss of one pedicle on AP view)
- Vertebral body collapse (not specific)
- Difficult to distinguish between infection and tumour on plain films
Bone scan (Tc 99)
- High sensitivity but low specificity
- Cannot differentiate cause of destruction from tumour and infection
- Multiple myeloma may not be detected
- CT localises and quantifies vertebral destruction
- CT assesses the surgical field
- Gold standard for evaluation of cord compression / epidural metastases
- Good at detection of metastases
- Anatomical definition of tumours
- Good at showing soft tissues and oedema
- Can help distinguish infection from tumour
- Assess highly vascularised tumours eg Aneurysmal Bone Cyst
- Selective embolisation can be useful prior to surgery
Although the universally known Enneking staging system is the standard for musculoskeletal tumours, recently there has been a move away from this system. It is perfectly acceptable to use Enneking's system but a better system is the Weinstein Biagini Boriani (WBB) system which takes into account the anatomy of the spine and offers surgical strategies based on the stage.
In terms of surgical resection the following terminology is accepted.
- Curettage - piecemeal removal / intralesional
- Marginal - dissection along the pseudocapsule
- En-Bloc or Wide - with continuous shell of healthy tissue
- Radical - tumour and whole compartment of tumour origin (impossible in spine)
- Palliative - intralesional / functional purpose
Enneking's staging system was introduced in 1980 and was designed to describe the risks of recurrence and provide treatment guidelines including adjuvant therapies. It is well known and used up to the late 1990s for spine and is the system of choice for other musculoskeletal regions. It requires a work up including plain films, CT scans, MRI scans, bone scans and a biopsy for accurate staging. It is a proven and validated system for long bone tumours.
There are three stages for both benign and malignant tumours.
Benign stage 1 - true capsule & well defined margins eg haemangioma grow slowly so no management required but intralesional if debulking required
Benign stage 2 - slender true capsule / do not extend beyond their compartment eg osteoid osteoma intralesional excision - low recurrence which can be improved further with adjuvant therapy
Benign stage 3 - aggressive / no capsule / extend outside compartment eg giant cell tumour marginal or en bloc resection required
|IA (low grade)||Intracompartmental||No Mets|
|IB (low grade)||Extracompartmental||No Mets|
|IIA (high grade)||Intracompartmental||No Mets|
|IIB (high grade)||Extracompartmental||No Mets|
|IIIA (any grade)||Intracompartmental||Mets|
|IIIB (any grade)||Extracompartmental||Mets|
The treatment principles are:
Stage 1A: Marginal excision with adjuvant therapy to decrease recurrence rate as there are residual foci of tumour
Stage 1B: En bloc excision required
Stage 2A & 2B: At lease en bloc excision reqd. Skip metastases mean that this may not be sufficient. Radical excision for stage 2B is possible in limbs but not spine.
Stage 3A & 3B: Same lesions as stage 2 but with metastasis. Treatment depends on individual tumour characteristics but often palliative
Problems with Enneking system with respect to the spine include the fact that the extent of lesions not truly defined (only intracompartmental or extracompartmental), the outcome not directly related to stage or grade and that one cannot define an adequate surgical margin accurately in the spine due to the presence of unresectable structures.
With these difficulties the WBB system was created. It was introduced 1991 and modified 1997 and is specific for the spine. It is designed for use after oncologic diagnosis and staging to guide treatment. It requires CT, MRI and possibly angiography required to perform staging. The vertebrae are divided into 12 pie like zones rotating clockwise and the depth of involvement is denoted A-E according to the degree of soft tissue involvement. This system allows surgeons to plan an en bloc excision by defining anatomically the tumour extent and therefore the lines of resection in tumour free zones. This system is briefly mentioned here for interest only and the reader is referred to the seminal paper on this subject for further details (see references).
The objectives are fivefold:
- Establish definitive diagnosis
- Conserve / restore neurological function
- Maintenance of spinal stability
- Pain relief
- Control of local/systemic spread
Non operative options include simple observation which is certainly appropriate for benign lesions. Bracing can aid spine stability if surgery is not feasible. Radiotherapy can be useful in alleviating cord compression caused by soft tissue elements without compromise of bony architecture. Some tumours are also particularly radiosensitive such as prostatic, breast and haemopoetic tumours. Chemotherapy is generally reserved for patients with systemic disease and similarly pain management only strategies are only suitable for end stage lesions.
Indications for operative surgery other than to achieve an en bloc excision include:
- Cord compression secondary to fracture or deformity resulting from tumour
- Instability - achievement of stability allows mobilisation
- Progressive pain
- Progressive neurology
- Isolated lesions unresponsive to nonoperative management
- The precise surgical strategies and approaches available involve a complex discussion with specialist spine surgeons and therefore should be referred to an appropriate unit for definitive management
- Rules for Making Human Tumour Cells, Hahn WC Weinberg RA – New England Journal Medicine 2002 347(20): 1593-1603
- Metastatic Disease of the Spine, Harrington KD – Journal of Bone and Joint Surgery (Am) 1986 68(7) 110-1115
- The Role of the Vertebral Veins in Metastatic Processes, Batson OV – Ann Intern Medicine 1942 16: 38-15
- Total Vertebrectomy for Primary Malignant Tumours of the Spine, Krepler P et al – Journal of Bone and Joint Surgery (Br) 2002 84(B) 712-5
- Primary Bone Tumours of the Spine, Boriani S Weinstein JN Biagini R – Spine 1997 22: 1036-1044
- Staging and Treatment of Primary Tumours of the Spine, Boriani S Bandiera S Biagini R Picci P – Current Opinion in Orthopaedics 1999 10: 93-100
- Total En Bloc Spondylectomy, Tomita K Kawahara N et al – Spine 1997 22: 324-333
- Primary and Metastatic Spinal Tumours, Austin L Grauer J et al – Core Knowledge in Orthopaedics: Spine (Mosby Elsevier) Chapter 17: 226-240
- Surgical Approach to Spine Tumours, Weinstein JN – Orthopaedics 12(6): 897-905
- Spinal Imaging, O'Donnell P – Spinal Imaging Course - Royal National Orthopaedic Hospital, Stanmore