Oligoastrocytomas (OAs) are intracranial tumors that are part of the glial cell continuum, with mixed oligodendroglial and astrocytic cell populations and typically occur in young adults.
The literature is somewhat conflicted on these entities, with imaging appearance and incidence varying widely. As of the latest (2016) update to the WHO classification of CNS tumors, their incidence will be greatly reduced .
Historically these tumors have in some institutions been encountered commonly, in some instances accounting for 50% of all oligodendrogliomas and considered the third most common glial neoplasm. However, it is not possible to infer a reliable incidence of oligoastrocytomas due to the vague criteria for their definition and wide interobserver variability .
The peak manifestation is during the 3 and 4 decades .
Oligoastrocytomas most commonly present with either partial or generalized seizures .
Oligoastrocytomas are WHO Grade II and anaplastic oligoastrocytomas are WHO Grade III.
Malignancy histologic features such as high cellularity, pleomorphism, nuclear atypia, and increased mitotic activity are usually found in the anaplastic oligoastrocytomas. Necrosis and microvascular proliferation may also be present but are not required for diagnosis .
As of the latest (2016) update to the WHO classification of CNS tumors, their incidence will be greatly reduced as the diagnosis will require molecularly distinct populations of both components to be identified: astrocytic (IDH-mutant, ATRX-mutant, 1p19q-intact) and oligodendrogliocytic (IDH-mutant, ATRX-wildtype, 1p19q co-deleted) .
On imaging, they have appearances that are essentially indistinguishable from their constituent tumors. There are no specific features to help separate oligoastrocytomas, astrocytomas and oligodendrogliomas.
Usually presented as an intra-axial low-attenuation area with little to no associated edema.
- T1: usually hypointense
- T2: usually hyperintense
- T1 C+ (Gd): usually non-enhancing lesions
Treatment and prognosis
Oligoastroctyomas respond less favourably to chemotherapy due to the chemoresistance of their astrocytic component . Studies have shown that the standard of care for oligodendroglial tumors that are 1p19q codeleted should be the combination of chemotherapy and radiation therapy .
A favorable prognosis is found in those with young age, WHO III, and better extent of resection .