Chordoma

Chordomas are uncommon malignant tumours that account for 1% of intracranial tumours and 4% of all primary bone tumours ³. 

They originate from embryonic remnants of the primitive notochord (earliest foetal axial skeleton, extending from the Rathke's pouch to the coccyx). Since chordomas arise in bone, they are usually extradural and result in local bone destruction. They are locally aggressive, but uncommonly metastasise. 

Epidemiology

Chordomas occur at any age but are usually seen in adults (30 - 60 years). Those located in the spheno-occipital region most commonly occur in patients 20 - 40 years of age, whereas sacrococcygeal chordomas are typically seen in a slightly older age group (peak 40 - 60 years). They are more common in Caucasians ³.

Clinical presentation

They are slow growing tumours and present due to mass effect on adjacent structures (brainstem, cranial nerves, nasopharynx, spinal cord), or as a mass (e.g. sacrococcygeal chordoma).

Pathology

Fluid and gelatinous mucoid substance (associated with recent and old haemorrhage) and necrotic areas are found within the tumour; in some patients, calcification and sequestered bone fragments are found as well. The variety of these components may explain the signal heterogeneity observed on MRI. Incomplete delineation of the tumour and microscopic distal extension of tumour cells may explain the frequency of recurrences. Physaliphorous cells are classically seen on microscopy

Metastatic spread of chordomas is observed in 7 - 14% of patients with lymph node, pulmonary, bone, cerebral, or abdominal visceral involvement, predominantly from massive tumours. True malignant forms of chordomas occasionally have areas of typical chordoma and undifferentiated areas, most often suggestive of fibrosarcoma; the prognosis is poor.

Location

Chordomas are found along the axial skeleton and a relatively evenly distributed among three locations :

• sacro-coccygeal : 30 - 50% ^2-3
• spheno-occipital : 30 - 35%
• vertebral body : 15 - 30%

Sacro-coccygeal

This is the most common location, accounting for approximately 30 - 50% ^2-3 of all chordomas, (particularly the fourth and fifth sacral segments) ². In this locaion a male predilection has been reported with a M:F ratio of 2:1. Chordomas in this location may be particularly large at presentation.

Chordoma  is the most common primary malignant sacral tumour.⁹

Spheno-occipital

The clival region is the next most common, accounting for 30 - 35% ^2-3 of cases. Typically the mass projects in the mid-line posteriorly indenting the pons. This characteristic appearance has been termed the 'thumb sign". In contrast to sacrococcygeal tumours there is currently no recognised gender difference.

Vertebral bodies

Chordomas of the vertebral bodies are rare but after lymphoproliferative tumours are nonetheless the most common primary malignancy of the spine in adults ². They most commonly involve the cervical spine (particularly C2), followed by the lumbar spine then the thoracic spine. They commonly extend across the intervertebral disc space, involving more than one vertebral segment. They may extend into the epidural space, compressing the spinal cord, or along the nerve roots, enlarging the neural exit foramen.  

Radiographic features

MRI and CT scan have complementary roles in tumour evaluation. CT evaluation is needed to assess the degree of bone involvement or destruction and to detect patterns of calcifications within the lesion. MRI provides excellent 3-dimensional analysis of the posterior fossa (especially the brainstem), sella turcica, cavernous sinuses, and middle cranial fossa. MRI depicts calcifications and the precise involvement of skull base osteolysis less well than CT, especially for skull base foramina.

CT

• centrally located
• well-circumscribed
• destructive lytic lesion, sometimes with marginal sclerosis
• expansile soft-tissue mass (usually hyper-attenuating relative to the adjacent brain, however inhomogenous areas may be seen due to cystic necrosis or haemorrhage; the soft-tissue mass is often disproportionately large relative to the bony destruction)
• irregular Intratumoral calcifications (thought to represent sequestra of normal bone rather than dystrophic calcifications)
• moderate to marked enhancement 

MRI

• T1
  • intermediate to low signal intensity
  • small foci of hyperintensity (intratumoral haemorrhage or a mucus pool)
• T2 : most exhibit very high signal 
• T1 C+ (Gd) : heterogeneous enhancement with a honeycomb appearance corresponding to low T1 signal areas within the tumour
• GE (gradient echo) : confirms haemorrhage if present with blooming

Bone scan

Normal or decreased uptake

Treatment and prognosis

Traditionally surgical resection has been the first line of treatment in feasible scenarios with radiotherapy offered for recurrent cases. Some advocate combination of radiation therapy and complete or subtotal surgical resection for selected patients ⁶. Percutaneous radiofrequncy ablation has been trialled as an adjunct ⁸ . Recurrence, including seeding along the operative tract, is common.

Prognosis is typically poor, due to the locally aggressive nature of these tumours, with the 10 year survival approximately 40%.

Differential diagnosis

For clival / spheno-occipitial lesions differentials to consider include: 

• chondrosarcoma of skull base
• plasmacytoma
• meningioma of skull base
• pituitary macroadenoma

For vertebral lesions, consider:

• chondrosarcoma
  • neural arch > vertebral body
  • thoracic spine is the most commonly involved spinal region
  • chondroid matrix (rings & arcs)
  • similar MRI appearance to chordomas (low to intermediate signal intensity on T1, hyperintense on T2, enhances)
• giant cell tumour
  • F>M
  • location: sacrum > thoracic spine > cervical spine > lumbar spine
  • no mineralised matrix
  • heterogenous intermediate to hype-rintense T2 signal
• spinal metastases
  • hypo-intense on T1; variably hyper-intense on T2
  • often multiple, involving vertebral bodies and posterior elements
• plasmacytoma
  • destructive vertebral body lesion (similar appearance to lytic metastases)
• spinal lymphoma
  • multifocal disease
  • heterogenous T2 signal