Oligoastrocytoma NOS

Case contributed by Dr Bruno Di Muzio


Not available.

Patient Data

Age: 45 years
Gender: Female


There is a diffuse irregular predominantly subcortical hypodensity within the inferior aspect of the left frontal lobe, although there is cortical involvement at the left frontal pole. This hypodensity involves the anterior aspect of the corpus callosum as well the genu, with resultant expansion of the corpus callosum. The abnormal hypodensity also extends via the corpus callosum into the deep white matter of the right frontal lobe. This corresponds to the intra-axial heterogeneous T1 signal, predominantly T2 hyperintense with partial FLAIR suppression, and at best wispy contrast enhancing intra-axial mass identified on the previous external MRI (not shown on this case). Within the inferior left frontal component, there are scattered foci of peripheral calcification. No acute hemorrhage within the mass. There is also significant surrounding white matter hypodensity, that extends posteriorly along bilateral external capsules, greater on the left. This mass causes almost complete effacement of the frontal horns of the lateral ventricles bilaterally. No hydrocephalus. No midline shift. No bony destruction of the floor of the anterior cranial fossa. No suspicious bony lesion.

IMPRESSION: Large intra axial mass with cortical involvement, centered within the inferior left frontal lobe with expansion of the anterior corpus callosum and extension across the midline into the right frontal lobe demonstrates speckled foci of peripheral calcification. When compared to the external MRI, the findings are almost certainly those of a primary brain tumor. Morphology and presence of calcification are suggestive of an oligodendroglioma or more likely an oligoastrocytoma, with either protoplasmic or gemistocytic astrocytic component (WHO II or III).




T2 hyperintensity and expansion straddling the midline is centered on the genu and anterior body of the corpus callosum, with signal abnormality extensively involving the frontal lobes bilaterally, the left insular and anterior temporal lobe, as well as bilaterally tracking inferiorly along the internal capsules. The lesion contains patchy areas of restricted diffusion. Although there are wispy areas of equivocal enhancement, there is no solid nodular enhancing component.

On diffusion studies, there is no cerebral blood volume (CBV) increase (not showed). Spectroscopy demonstrates an unusual trace with marked metabolite lesion but no associated lactate peak (not showed).

There is localised mass effect on frontal sulci and suprasellar cistern, but no uncal or descending transtentorial herniation.

IMPRESSION: Unusual constellation of findings. On morphologic grounds, lesion straddling the anterior corpus callosum would be most consistent with a glioblastoma, possibly ex-oligodendroglioma given presence of calcification on CT. The absence of significant enhancement and cerebral blood volume (CBV) increase would be atypical, although can be seen secondary to high-dose steroid therapy. The spectroscopy trace is very unusual for tumor, but the morphologic features and distribution still strongly favour GBM over alternate pathologies such as ischemia.



MICROSCOPIC DESCRIPTION: 1-2. Sections show cerebral cortex and white matter. There is a moderately cellular glial tumor. There is a proliferation of predominantly neoplastic oligodendroglial cells. They have enlarged round nuclei with perinuclear haloes. Intermixed neoplastic astrocytes are also present. These cells have more elongated and angulated nuclei. The background is fibrillary with cystic spaces and occasional calcification. The tumor extends into the cortex with secondary structuring including subpial accumulation and perineuronal satellitosis. A single mitosis is identified. No microvascular proliferation or necrosis is present.

IMMUNOHISTOCHEMISTRY: GFAP positive in tumor and reactive astrocytes; negative in tumor oligodendroglial cells NogoA positive in tumor oligodendroglial cells. IDH-1 R132H positive (mutated) ATRX positive (not mutated) MGMT positive (likely unmethylated) p53 negative p16 positive Topoisomerase labelling index: Approximately 2% The features are those of oligoastrocytoma (WHO Grade II).

DIAGNOSIS: oligoastrocytoma (NOS) (WHO Grade II) 

Case Discussion

Oligoastrocytomas (NOS) are tumors composed histologically of a mixture of two neoplastic cell types: oligodendrogliomas and diffuse astrocytomas. They are classified as WHO grade II or III. 

NOTE: This case predates the 2016 WHO classification of CNS tumor 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: 34625
Published: 3rd Mar 2015
Last edited: 16th Jul 2018
Tag: rmh
Inclusion in quiz mode: Included

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