Chordoma
A chordoma is an uncommon malignant tumour which accounts 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 can uncommonly metastasise.
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 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.
Demographics and clinical presentation
Chordomas occur at any age but are usually seen in adults (30 - 60 years) and are more common in Caucasians 3. They are slow growing tumours and present due to mass effect on adjacent structures (brainstem, cranial nerves, nasopharynx).
Location
Chordomas are found along the axial skeleton and a relatively evenly distributed among three locations :
- sacrococcygeal : 30 - 50% 2-3
- spheno-occipital : 30 - 35%
- vertebrae : 15 - 30%
Sacrococcygeal
Sacrococcygeal location is most common, 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.
Spheno-occipital
Clival chordomas are 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) or lumbar vertebrae.
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
- expansile soft-tissue mass (usually hyper-attenuating relative to the adjacent brain)
- irregular Intratumoral calcifications (thought to represent sequestra of normal bone rather than dystrophic calcifications)
- moderate to marked enhancement
MRI
3-D gradient-echo T1-weighted sequences are helpful since they visualize the tumor in 3 planes within a short time and with good analysis of tumoral signal.
- T1 :
- intermediate to low signal intensity
- small foci of hyperintensity (intratumoral haemorrhage or a mucus pool)
- heterogeneous enhancement with a honeycomb appearance corresponding to low T1 signal areas within the tumour
- T2 : most exhibit very high signal on T2-weighted images
- GE : confirms haemorrhage if present with blooming
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 trilled as an adjunct 8 .
