Chordomas are uncommon malignant tumours that account for 1% of intracranial tumours and 4% of all primary bone tumours.
They originate from embryonic remnants of the primitive notochord (earliest fetal 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.
Chordomas occur at any age but are usually seen in adults (30-70 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 around 50 years 10). They are commonly found in Caucasians 3.
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 and includes nodal, 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.
Chordomas are found along the axial skeleton and a relatively evenly distributed among three locations:
- sacrococcygeal: 30-50% 2-3
- spheno-occipital: 30-35%
- vertebral body: 15-30%
This is the most common location, accounting for approximately 30-50% 2-3 of all chordomas and involving particularly the fourth and fifth sacral segments 2. In this location a male predilection has been reported (M:F ratio of 2:1)nd the tumour may be particularly large at presentation 10.
Chordoma is the most common primary malignant sacral tumour 9-10.
The clival region is the next most common, accounting for 30-35% 2-3 of cases. Typically the mass projects in the midline 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.
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 often 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.
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.
- centrally located
- 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
- 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
- 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 the combination of radiation therapy and complete or subtotal surgical resection for selected patients 6. Percutaneous radiofrequency 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%.
For clival/spheno-occipitial lesions differentials to consider include:
- chondrosarcoma of skull base
- meningioma of skull base
- pituitary macroadenoma
- ecchordosis physaliphora
For vertebral lesions, consider:
- 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
- location: sacrum > thoracic spine > cervical spine > lumbar spine
- no mineralised matrix
- heterogeneous intermediate to hyperintense T2 signal
- hypointense on T1; variably hyperintense on T2
- often multiple, involving vertebral bodies and posterior elements
- destructive vertebral body lesion (similar appearance to lytic metastases)
- multifocal disease
- heterogenous T2 signal
The differential diagnosis for bone tumours is dependent on the age of the patient, with a very different set of differentials for the paediatric patient.
- bone-forming tumours
- cartilage-forming tumours
- chondromyxoid fibroma
- fibrous bone lesions
- bone marrow tumours
- other bone tumours or tumour-like lesions
- aneurysmal bone cyst
- benign fibrous histiocytoma
- giant cell tumour of bone
- Gorham massive osteolysis
- haemophilic pseudotumour
- intradiploic epidermoid cyst
- intraosseous lipoma
- musculoskeletal angiosarcoma
- musculoskeletal haemangiopericytoma
- primary intraosseous haemangioma
- simple bone cyst
- impending fracture risk
Pituitary region masses
- pituitary adenoma (commonest in the adult population)
- hypothalamic astrocytoma/glioma
- chiasmatic astrocytoma
- optic nerve glioma
- dermoid (CNS) / epidermoid / intracranial teratoma
- pituitary metastases
- granular cell tumour of the pituitary (pituitary choristoma)
- pilocytic astrocytoma of the neurohypophysis (infundibuloma)
- cellular infiltrates
- other lesions
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