General
- Chondrosarcomas are a family of malignant mesenchymal tumours with cartilaginous differentiation.
- Most chondrosarcomas arise de novo, but some develop in a pre-existing benign cartilaginous lesion
- This family comprises conventional central, dedifferentiated central, conventional peripheral, dedifferentiated peripheral, and clear cell chondrosarcomas.
Definition
- Essential
- Histologically malignant tumour with cartilaginous differentiation.
- The diagnosis must also be supported by an immunohistochemical profile characteristic of chondrosarcoma.
Epidemiology
- Intracranial chondrosarcomas account for approximately 1 per cent of all chondrosarcomas.
- At this site, they are encountered less frequently than chordomas.
- In a study of 200 patients with skull base tumours, the mean age was 39 years, with a range from 10 to 79 years.
- The sex ratio in that study was reported as 1:1.3 (male to female).
Grading
- Conventional chondrosarcomas of the central nervous system are assigned CNS WHO grades 1, 2, or 3.
- Most chondrosarcomas arising in the skull base are low-grade (CNS WHO grade 1).
- Grading criteria
- Grade 1 tumours generally have uniform nuclei and frequent binucleation, but mitoses are absent.
- Grade 2 tumours show increased cellularity, a greater degree of nuclear atypia, and the presence of mitoses.
- Grade 3 tumours are highly cellular, more pleomorphic, and mitoses are easily found.
Histopathology
- Macroscopic
- These tumours typically appear as firm, glistening, grey lobular masses.
- They are usually non-haemorrhagic, though they may have mucinous areas if myxoid change is present.
- Skull base tumours are often resected in a piecemeal fashion.
- Microscopic
- Hyaline-type conventional chondrosarcomas are moderately cellular and consist of polyhedral cells in lacunar spaces within a solid basophilic matrix.
- Myxoid-type tumours feature spindle and stellate cells floating in a basophilic, flocculent, mucinous matrix.
- In these patterns, cells do not form cohesive nests, but processes of adjacent cells may interconnect.
- Dedifferentiated chondrosarcomas show an abrupt transition from low-grade to high-grade phenotypes, such as pleomorphic spindle cell sarcoma.
(A) Low-grade chondrosarcoma may show small stellate to epithelioid cells set within a myxoid background, overlapping morphologically with chordoma.
(B) S100 immunoreactivity is typically strong in low-grade chondrosarcomas, but is not very specific, because it may also be seen in other diagnostic considerations, such as chordoma.
(C) Lack of nuclear brachyury expression helps distinguish chondrosarcoma from chordoma.
(D) The combination of a small blue cell tumour with well-formed hyaline cartilage is characteristic of mesenchymal chondrosarcoma.
- Immunophenotype
- Tumour cells typically show immunoreactivity for S100 and D2-40 (podoplanin).
- They are negative for cytokeratin and brachyury, which distinguishes them from chordoma.
- Approximately 6 per cent of chondrosarcomas are positive for EMA.
- Dedifferentiated areas may show a loss of H3 p.K28me3.
Pathogenesis
- 60 per cent of central cartilaginous tumours harbour a mutation in IDH1 or IDH2.
- These mutations are common in skull base chondrosarcomas, while tumours of the facial skeleton lack them.
- Mosaic IDH mutations occurring as early postzygotic events cause disorders such as Ollier disease and Maffucci syndrome.
- Individuals with multiple osteochondromas due to germline EXT1 or EXT2 mutations have a higher risk of secondary peripheral chondrosarcoma.
Localisation
- Conventional chondrosarcoma is the most common tumour type arising in the cranial bones.
- Typical sites include the skull base (specifically spheno-occipital and sphenopetrosal synchondroses), spine, and sacrum.
- Parenchymal intracranial, meningeal, and extraosseous examples are considered rare.
Clinical features
- Patients typically present with a painful, enlarging mass.
- Neurological symptoms are dependent on the specific site; for instance, skull base tumours may cause cranial nerve palsies.
Radiological features
- Computed tomography often demonstrates a heavily calcified mass at the skull base.
- Magnetic resonance imaging usually shows a heterogeneous signal.
- On T1-weighted images, these tumours are generally hypointense compared to adjacent muscle, and they show heterogeneous contrast enhancement.
Management
- Management typically involves surgical resection.
- Adjuvant therapy, such as proton beam therapy or radiosurgery, is frequently required due to the locally destructive nature of the tumour.
Prognosis
- Most skull base chondrosarcomas are low-grade primary tumours.
- Although they are locally destructive, metastases from these tumours are rare.
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