Gliosarcomas are a variant of glioblastoma (along with epithelioid glioblastoma and giant cell glioblastoma) recognized in the current (2016) WHO classification of CNS tumors . 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 .
Peak presentation is around the 6 decade and there is a male predilection (M:F 1.8:1) . Most tumors are primary but secondary tumors 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 tumor comprises both glial and mesenchymal elements, there is evidence that both components arise from a solitary precursor cell .
They are almost invariably found in the cerebral hemispheres, and there may be slight predilection towards the temporal lobes .
These tumors 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 .
Microscopically, these tumors 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 . Differentiation into may other types of tissue is also occasionally encountered (cartilage, bone, adipose, muscle) .
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) .
Gliosarcomas may be seen on CT as a sharply defined (often due to sarcomatous component ), round or lobulated, hyperdense solid mass. They can have relatively homogeneous contrast enhancement and peritumoral edema.
Reported signal characteristics include:
- T1: heterogeneous and hypointense mass
- T2: heterogeneous signal due to hemorrhagic and necrotic components
- T1C+ (Gd): thick irregular and rim-like or ring enhancement
On angiography, mixed dural and pial vascular supply may be present . Early cortical venous drainage, irregular tumor vessels, and a prominent vascular stain with well-defined tumor margins may also be seen.
Treatment and prognosis
As with glioblastomas, this tumor carries a very poor prognosis. Extracranial metastases can occur in up to 30% of cases.
General imaging differential considerations include:
- glioblastoma: often indistinguishable from gliosarcoma
- cerebral metastasis: appear very similar if sarcomatous component of gliosarcoma is dominant
- meningioma or hemangiopericytoma: if mass is attached to the dura