ARTICLES Uncategorized
By: 1 December 2009

Introduction


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.

Basic Science


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.

  1. Self sufficiency from growth factors
  2. Resistance to growth - inhibitory factors
  3. Resistance to apoptosis
  4. Immortalization (ability to endlessly proliferate)
  5. 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.

  1. Tumours derived from osteoblast typically show active ossification and calcification eg osteoid osteoma, osteosarcoma.
  2. Those derived from the fibroblast line typically show collagen formation eg fibroma, fibrous histiocytoma.
  3. Chondroblast derived tumours show cartilage in their architecture eg osteochondroma, chondrosarcoma
  4. 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)

Investigations


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.

Plain films

  • 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

  • CT localises and quantifies vertebral destruction
  • CT assesses the surgical field

MRI

  • 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