Oligoastrocytoma

A.Prof Frank Gaillard et al.

Oligoastrocytomas (OAs) are intracranial tumours 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 tumours their incidence will be greatly reduced 8.  

Historically these tumours have in some institutions been encountered commonly, in some instances accounting for 50% of all oligodendrogliomas and considered the third most common glial neoplasm 2. However, it is not possible to infer a reliable incidence of oligoastrocytomas due the vague criteria for their definition and wide interobserver variability 6.

The peak manifestation is during the 3rd and 4th decades 1.

Oligoastrocytomas most commonly present with either partial or generalised seizures 7.

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 the diagnosis 1.

As of the latest (2016) update to the WHO classification of CNS tumours their incidence will be greatly reduced as 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) 8

On imaging they have appearances that are essentially indistinguishable from their constituent tumours. There are no specific features to help separate oligoastrocytomas, astrocytomas and oligodendrogliomas. 

CT

Usually presented as an intra-axial low-attenuation areas with little to no associated oedema.

MRI
  • T1: usually hypointense
  • T2: usually hyperintense 
  • T1 C+ (Gd): usually non-enhancing lesions 

Oligoastroctyomas respond less favourably to chemotherapy due the chemoresistance of their astrocytic component 4. Studies have shown that the standard of care for oligodendroglial tumours that are 1p19q codeleted should be the combination of chemotherapy and radiation therapy 5.

A favourable prognosis is found in those with young age, WHO III, and better extent of resection 3.

Astrocytic tumour
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Article information

rID: 1771
Section: Pathology
Synonyms or Alternate Spellings:
  • Oligoastrocytomas
  • OAs
  • Mixed glioma

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Cases and figures

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    Figure 1: histology H & E
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    Case 1: CT
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    Figure 2: histology
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    Case 1: FLAIR
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    Figure 3: histology
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    Case 2: T1 C+
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    Case 3: T1 C+
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    Case 4
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    Case 5: haemorrhagic
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    Case 6
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    Case 7: mixed oligoastrocytoma
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    Case 9: bifrontal extension
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