Anaplastic oligoastrocytoma NOS

Case contributed by A.Prof Frank Gaillard
CT

CT brain (single image)

Heterogeneous region of contrast enhancement, oedema and mass effect is present in the left frontal lobe. 

MRI

MRI brain

MRI including post contrast sequences demonstrates a large mass involving the majority of the left frontal lobe, which exerts significant mass effect resulting in midline shift and effacement of the frontal horn of the lateral ventricle. 

The mass is heterogeneous, but predominantly low on T1 and high on T2 with a surrounding mantle of tumour oedema. Following contrast there is heterogeneous moderate enhancement. 

The patient went on to have a craniotomy and debulking of the mass. 

Histology

Microscopic Description:

The sections show a glial neoplasm that diffusely infiltrates brain tissue. The tumour is remarkable for the variety of histologic appearances. Many areas show definite oligodendroglioma differentiation with uniform round cells surrounded by perinuclear halos associated with capillary proliferation and focal microcalcification. In focal areas, this portion of the tumour becomes more cellular and shows a greater degree of nuclear pleomorphism and rare mitotic figures. Other areas show definite astrocytic differentiation, including both gemistocytic and pilocytic morphology. Rare mitotic figures are present in the gemistocytic areas. Finally, areas composed of cells with relatively uniform small round nuclei and short delicate processes associated with prominent microcystic architecture could either represent oligodendroglioma or protoplasmic astrocytoma. Vascular changes include hyalinized vessels and focal aggregates of dilated capillary vessels resembling telangiectasia. No endothelial proliferation or necrosis is identified. Large neurons are scattered throughout the tumour, however, these appear to represent entrapped normal cortical neurons.

Final Diagnosis:

This tumour shows distinct areas of both oligodendroglioma and astrocytoma (oligoastrocytoma). Although much of the tumour appears to be low grade, the presence of some mitotic activity in the more poorly differentiated portions of the oligodendroglioma as well as the gemistocytic areas of astrocytoma are worrisome and suggest this tumour should be graded as III. 

Case Discussion

Sometimes tumours do not fall nicely into a single histological category, and this makes prognosis and treatment difficult. In general, the worst component should be used to guide management. 

NOTE: This case predates the 2016 WHO classification of CNS tumour revision. As no 1p19q co-deletion status is available a formal diagnosis cannot be reached and the NOS is therefore used (not otherwise specified) - which is recognised in the current classification for cases where molecular information is unavailable.

It should also be noted, that under the new classification both an astrocytic and oligodendroglial component needs to be identified, each with its own molecular markers. True oligoastrocytomas are therefore going to be rare, and this case would most likely be classified as either an astrocytoma or an oligodendroglioma. 

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Case information

rID: 4654
Case created: 26th Sep 2008
Last edited: 20th May 2017
Inclusion in quiz mode: Included

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