Gliosarcomas are a variant of glioblastoma (along with epithelioid glioblastoma and giant cell glioblastoma) recognised in the current (2016) WHO classification of CNS tumours 9. They are highly malignant (WHO grade IV) primary intra-axial neoplasms with both glial and mesenchymal elements.
The vast majority of gliosarcomas arise from WHO grade IV astrocytomas (i.e. glioblastoma), however, rarely they can also arise from ependymomas or oligodendrogliomas in which case they can be referred to as ependymosarcomas and oligosarcomas respectively 9.
Peak presentation is around the 6th decade and there is a male predilection (M:F 1.8:1) 1,9. Most tumours are primary but secondary tumours can occur in patients with previously resected glioblastomas or cranial irradiation.
Gliosarcomas are very similar to glioblastomas but with an added sarcomatous component. Although the tumour comprises of both glial and mesenchymal elements, there is evidence that both components arise from a solitary precursor cell 9.
They are almost invariably found in the cerebral hemispheres, and there may be slight predilection towards the temporal lobes 1,9.
These tumours vary in appearance depending on the relative amounts of sarcomatous tissue and astrocytic tissue. When the former is dominant, then these lesions appear similar to metastases; well circumscribed and firm. When the astrocytic component is abundant, then appearances are identical to a glioblastoma 9.
Microscopically, these tumours show both an astrocytic component identical to glioblastomas and a sarcomatous component which is varied in differentiation, typically with epithelial components forming squamous tissue or gland-like structures 9. Differentiation into may other types of tissue is also occasionally encountered (cartilage, bone, adipose, muscle) 9.
Gliosarcomas can be very similar to glioblastomas in appearance. They are usually broad-based peripherally located lesions with possible direct dural invasion or only reactive dural thickening (dural tail) 3-7.
Gliosarcomas may be seen on CT as a sharply defined (often due to sarcomatous component 5), round or lobulated, hyperdense solid mass. They can have relatively homogeneous contrast enhancement and peritumoral oedema.
Reported signal characteristics include:
- T1: heterogeneous and hypointense mass
- T2: heterogeneous signal due hemorrhagic and necrotic components
- T1C+ (Gd): thick irregular and rim-like or ring enhancement 8
On angiography, mixed dural and pial vascular supply may be present 3. Early cortical venous drainage, irregular tumour vessels, and a prominent vascular stain with well-defined tumour margins may also be seen.
Treatment and prognosis
As with glioblastomas, this tumour carries a very poor prognosis. Extracranial metastases can occur in up to 30% of cases.
General imaging differential considerations include:
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- WHO classification of CNS tumours
- WHO grading of CNS tumours
- VASARI MRI feature set
- diffuse astrocytoma grading
- grade I:
- grade II:
- grade III
- grade IV:
- glioblastoma vs cerebral metastasis
- radiation-induced gliomas
- gliomatosis cerebri (growth pattern)
- specific locations
- treatment response
- Stupp protocol
- glioma treatment response assessment in clinical trials
- multicentric glioblastoma
- multifocal glioblastoma
- prognostic genetic markers