Primary Bone Tumors of the Spine

Primary malignant bone tumours of the spine are rare, only 5% of all spinal tumours, and they need management quite distinct from that of metastases. The most common are chordoma, chondrosarcoma, osteosarcoma and Ewing sarcoma.

Who gets which. Chordoma and chondrosarcoma are tumours of adulthood, while Ewing sarcoma and osteosarcoma mainly affect children and young adults. Age at presentation helps narrow the differential diagnosis, and so does location.

Where chordoma arises. Chordoma, the most common primary malignant tumour of the spine, arises from notochord remnants along the neuraxis. The figures examiners expect are sacrococcygeal 50%, skull base (clivus) 35%, mobile spine 15%, and within the mobile spine the cervical region is more commonly affected than the thoracic or lumbar. Learn them, but know where they come from.

What the population data show. That split derives from surgical case series, and the population-based data disagree: the SEER analysis of 400 microscopically confirmed chordomas found 29.2% sacral, 32.8% mobile spine and 32% cranial (McMaster, PMID 11227920), roughly equal thirds. The classic ratio over-weights the sacrum because sacral chordomas grow silently until large and are referred to surgical centres, while skull-base disease presents to neurosurgery and small mobile-spine tumours are found incidentally. Quote 50/35/15 in an exam; do not use it to argue a lesion is unlikely to be chordoma because of its level.

Enneking's system is the standard staging for musculoskeletal tumours. The Weinstein-Boriani-Biagini (WBB) system is an anatomical staging specific to the spine and guides the planning of en bloc resection. No specific staging system exists for chordoma, which is staged with Enneking combined with its anatomical location.

Enneking StagingWBB StagingWHO Classification

IA

Grade

Low (G1)

Compartment

Intracompartmental

Metastases

M0

IB

Grade

Low (G1)

Compartment

Extracompartmental

Metastases

M0

IIA

Grade

High (G2)

Compartment

Intracompartmental

Metastases

M0

IIB

Grade

High (G2)

Compartment

Extracompartmental

Metastases

M0

III

Grade

Any

Compartment

Any

Metastases

M1

Stage	Grade	Compartment	Metastases
IA	Low (G1)	Intracompartmental	M0
IB	Low (G1)	Extracompartmental	M0
IIA	High (G2)	Intracompartmental	M0
IIB	High (G2)	Extracompartmental	M0
III	Any	Any	M1

Stage III covers any grade with regional or distant metastases. Most spine tumours at presentation are Stage IIB (extracompartmental) because of the anatomical complexity of the spine.

Sectors and layers. WBB divides the vertebra like a clock face into 12 radiating zones: zones 4 to 9 are the vertebral body and zones 10 to 3 the posterior elements. It adds five tissue layers:

• A: extraosseous soft tissue
• B: intraosseous superficial
• C: intraosseous deep
• D: extraosseous extradural (epidural)
• E: extraosseous intradural

What it decides. Recording which zones and layers a tumour occupies shows whether a tumour-free en bloc margin is anatomically achievable and which surgical approach is required.

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The 2020 WHO classification of bone tumours groups the spinal entities below. WHO grading correlates with prognosis and guides treatment.

Notochordal

Entities

Benign notochordal cell tumour; chordoma (conventional, chondroid, dedifferentiated)

Chondrogenic

Entities

Chondrosarcoma (grade I, II, III); dedifferentiated chondrosarcoma; mesenchymal chondrosarcoma

Osteogenic

Entities

Osteosarcoma (conventional and subtypes); secondary osteosarcoma

Ewing sarcoma family

Entities

Ewing sarcoma (defined by fusion gene)

Family	Entities
Notochordal	Benign notochordal cell tumour; chordoma (conventional, chondroid, dedifferentiated)
Chondrogenic	Chondrosarcoma (grade I, II, III); dedifferentiated chondrosarcoma; mesenchymal chondrosarcoma
Osteogenic	Osteosarcoma (conventional and subtypes); secondary osteosarcoma
Ewing sarcoma family	Ewing sarcoma (defined by fusion gene)

Pain. Pain is the most common presentation: localised back pain, often insidious in onset and typically progressive over months. It may be mechanical or constant, and night pain and rest pain are common.

Neurology. Nerve root compression produces radiculopathy, cord compression produces myelopathy, and sacral tumours can cause cauda equina syndrome. Bowel and bladder dysfunction comes late.

Chordoma. A sacral chordoma gives low back pain, sciatica, constipation and urinary symptoms, and may present as a palpable presacral mass on rectal examination. At the skull base it causes cranial nerve palsies and headache.

Ewing sarcoma. It often presents with systemic symptoms (fever, weight loss, raised inflammatory markers) and may mimic infection.

Osteosarcoma. Pain and swelling, a possible pathological fracture, and a raised alkaline phosphatase.

Red flags.

• Pain worse at night or at rest
• Progressive neurological deficit
• Weight loss, fever
• Palpable mass
• Pathological fracture

Site and age first. This page covers the primary malignant tumours, but the first sieve for any primary spinal bone tumour is where in the vertebra it sits and the patient's age, which also flags the common benign primaries.

• Posterior elements: osteoid osteoma, osteoblastoma, aneurysmal bone cyst, chondrosarcoma
• Vertebral body: haemangioma, giant cell tumour, chordoma, eosinophilic granuloma (Langerhans cell histiocytosis, classically causing vertebra plana in a child), metastasis, myeloma
• Under about 30 and benign-looking: osteoid osteoma, osteoblastoma, ABC or eosinophilic granuloma
• Under about 30 and aggressive: Ewing sarcoma or osteosarcoma

A painful scoliosis with night pain relieved by NSAIDs in a teenager is the classic osteoid osteoma or osteoblastoma story. Place the lesion in this location-plus-age grid before committing to a diagnosis.

The adult over 40. A destructive vertebral lesion in any adult over 40 is statistically far more likely to be a metastasis or myeloma than a primary sarcoma, with chordoma and chondrosarcoma the leading primary malignant possibilities. The management of a primary tumour (en bloc resection, excision of the biopsy tract) is so different that it must be actively excluded before any intervention.

Radiographs. Often the first imaging, but their sensitivity is limited and they may be normal in early disease, so advanced imaging is always required. Look for a lytic or sclerotic pattern, bone destruction, matrix mineralisation and a soft-tissue mass.

CT. The best study of bone architecture. It characterises the matrix (calcification, osteoid), assesses fracture and is essential for surgical planning and biopsy guidance. CT angiography is useful for vascular mapping before surgery.

MRI. The gold standard, essential for every primary spine tumour. Image the whole spine to assess skip metastases.

• T1: anatomical detail, marrow replacement
• T2/STIR: tumour extent, oedema
• Post-contrast: enhancement pattern, vascularity
• DWI: cellularity

Nuclear medicine. A bone scan has limited sensitivity for primary tumours, and chordoma may be cold, but it is useful for screening for skeletal metastases. PET-CT is increasingly used for staging metastatic disease and assessing treatment response: FDG uptake correlates with grade and SUV with prognosis. Low-grade tumours may be FDG-negative, and post-treatment change confounds interpretation.

Tumour-specific appearances.

Reading the calcification. Ring-and-arc calcification is pathognomonic of a chondroid matrix, not of malignancy: enchondroma, osteochondroma and chondroblastoma produce the identical pattern. What makes a lesion chondrosarcoma is the company the matrix keeps, a destructive soft-tissue mass, not the arcs themselves.

Biopsy. CT-guided biopsy is preferred in the spine, through a tract that avoids contaminating multiple compartments.

Chemosensitivity decides the pathway. Chordoma and chondrosarcoma are not chemosensitive and are resistant to conventional radiation, so surgery is the primary treatment and wide en bloc resection is the only curative option. Ewing sarcoma and osteosarcoma are chemosensitive, and chemotherapy is integral to their treatment; Ewing sarcoma is highly radiosensitive as well.

Algorithm

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Margins. The goal of en bloc resection is a negative margin without violating the tumour capsule. Enneking's margin types carry very different local recurrence rates:

• Intralesional: through the tumour, contaminating the field; recurrence approaching 100%
• Marginal: through the reactive zone; 50-70%
• Wide: through normal tissue, with a cuff around the tumour; 20-30%
• Radical: the entire compartment, rarely achievable in the spine

En bloc vertebrectomy is technically demanding and requires an experienced spine oncology team.

Sacral tumours. Sacral chordoma is resected through a combined anterior-posterior approach, and the level of resection determines function (the roots are set out under Complications). Preoperative embolisation reduces blood loss, rectal involvement may require a colostomy, and the complication rate is high (wound, infection, neurological). Reconstruction uses spinopelvic instrumentation, bone graft or a cage, and a soft-tissue flap for wound coverage.

Mobile spine. En bloc spondylectomy is a total vertebrectomy including the posterior elements, often staged, with circumferential reconstruction. It achieves the best margins but carries the highest morbidity. The WBB zones involved determine the approach, together with whether one or several levels are involved and whether there is epidural (layer D) involvement. The spinal cord cannot be sacrificed, and involvement of an adjacent level increases the difficulty.

Chordoma and chondrosarcoma. Chemotherapy is not effective. Proton or carbon-ion therapy may improve local control, and targeted therapy (imatinib, EGFR inhibitors) is under investigation.

1. Staging (MRI, CT, PET)
2. Biopsy, coordinated with the surgeon
3. En bloc resection with wide margins
4. Consider proton therapy if margins are positive

Osteosarcoma. Neoadjuvant chemotherapy is mandatory, on the MAP protocol, and surgery follows it. Histological response predicts prognosis.

1. Staging
2. Neoadjuvant chemotherapy (10-12 weeks)
3. Surgical resection
4. Adjuvant chemotherapy based on necrosis

Ewing sarcoma. Chemotherapy is given before and after surgery, VDC/IE is the standard protocol, and radiation is added if margins are inadequate.

1. Staging, including whole-body PET
2. Neoadjuvant chemotherapy
3. Surgery or radiation (or both)
4. Maintenance chemotherapy

Early. Wound complications are the most common, especially after sacral resection. The others are cerebrospinal fluid leak, neurological deficit and massive blood loss, on average 2-5 L for sacral tumours.

Late. Hardware failure, pseudarthrosis, adjacent level disease and chronic pain.

Sacral resection: count the roots preserved. The severity runs from the top down: losing S2 costs more than losing S3, because every root below the cut goes with it. The reference figures are Todd's 53-patient Mayo series (PMID 11953593):

The rules. Bilateral preservation of S2 and at least one S3 is generally needed to retain useful bladder, bowel and sexual function, and losing both S3 roots (a bilateral cut at or above S3) typically produces neurogenic bladder and bowel and sexual dysfunction. Unilateral sacrifice of even all the sacral roots on one side is usually tolerated with preserved continence, provided the contralateral S2-S4 are intact. Resection below S3 bilaterally usually preserves continence, with some saddle numbness.

Bladder is the weaker organ at every level. Even with both S3 roots preserved only about two-thirds keep normal bladder function, against near-universal bowel continence, so consent for bladder dysfunction must be more pessimistic than for bowel. These are retrospective, single-centre, surgeon-graded outcomes over ten years with no urodynamics: read them as counselling anchors, not guarantees.

Stability is a separate question. S1 sacrifice adds plantarflexion weakness, and bilateral S1 loss also threatens spinopelvic continuity. A cut through or above S1 divides the weight-bearing ala and disrupts the pelvic ring, mandating lumbopelvic (spinopelvic) reconstruction, whereas low sacrectomies below S1 usually do not.

Mobile spine. Nerve roots may have to be sacrificed for clear margins, and en bloc techniques carry a risk of spinal cord injury.

Local recurrence. The risk factors are intralesional rather than en bloc surgery, positive surgical margins, tumour grade and dedifferentiated histology. Recurrence is managed by re-resection if feasible, radiation therapy (proton or carbon ion), or palliative care if unresectable.

En Bloc Spine Tumour Resection Protocol

Margin status comes first. For chordoma and chondrosarcoma, surgical margin status is the most important prognostic factor, and proton beam therapy can help salvage a positive margin. The other prognostic factors in chordoma are histological subtype, tumour size and location, the skull base having the worst access.

Global epidemiology

Primary malignant bone tumours of the spine are rare, accounting for only a small fraction of spinal tumours; the spine is far more commonly affected by metastatic disease. Chordoma is the most frequent primary malignant tumour of the mobile spine and is itself uncommon. The age distribution is bimodal across the group: chordoma and chondrosarcoma predominate in adults (typically 40-70 and 30-70 years respectively), whereas Ewing sarcoma and osteosarcoma cluster in children and young adults. Across reported series there is a modest male predominance for chordoma. The largest contemporary outcome data come from multicentre registries rather than single-country health systems.

Major guidelines, side by side

A consistent thread across all bodies is that biopsy must be planned by the treating sarcoma team, because a poorly placed tract can render a curative en bloc resection impossible.

Registry and multicentre evidence

Because each centre sees few cases, the strongest evidence is pooled. The AOSpine Knowledge Forum Tumour databases have quantified that Enneking-appropriate en bloc surgery improves survival and local control in spinal Ewing sarcoma and osteosarcoma. For radiotherapy, the Proton Collaborative Group prospective registry and large single-institution proton cohorts demonstrate high local control with low high-grade toxicity. These collaborations function as the de-facto registries for these rare tumours.

Global practice variation

The principal variation worldwide is access to particle therapy. Proton and carbon-ion facilities are concentrated in a limited number of centres in North America, Europe and Asia; carbon-ion therapy in particular is largely confined to dedicated centres (notably in Japan and Europe). In settings without particle therapy, management relies more heavily on achieving a wide en bloc margin and on high-dose photon techniques. Centralisation of these rare tumours to high-volume sarcoma units is recommended in every health system, as surgeon and centre experience correlate with margin achievement and outcome.

Given the rarity and complexity of these tumours, referral to a specialist sarcoma service is strongly recommended for all patients with a suspected primary malignant spine tumour before any biopsy is performed.

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