Oligoastrocytoma NOS (anaplastic)

Case contributed by Rajalakshmi Ramesh
Diagnosis certain


G1P1, presenting with a generalized tonic-clonic seizure postpartum.

Patient Data

Age: 40-year-old
Gender: Female

CT Brain


A mass of heterogeneous density measuring 3cm with minor calcification is seen in the right frontal lobe. Local minor mass effect. Ventricular size and position are normal. The differential diagnosis is unchanged from the MR report with appearances suggesting a low grade tumor.

MRI Brain


A mass lesion lies in the middle frontal gyrus on the right. It demonstrates a medial peripheral zone of increased signal on T1 without evidence of signal dropout on the T2 weighted scans. There is no real evidence to suggest blood products. No subarachnoid blood. No evidence of central venous thrombosis. Although the lesion is a relatively high signal on the diffusion weighted imaging the ADC shows no decrease, no restricted diffusion. The lesion infiltrates anteriorly into the adjacent anterior frontal gyrus. Little if any surrounding vasogenic edema. After injection of gadolinium, minor enhancement of the medial and inferior portion of the lesion is suspected. No other contrast enhancing or white matter lesions are identified. No evidence of bony remodeling of the overlying diploic space. MR spectroscopy shows decreased NAA and elevated Choline and mI, suggesting a tumor trace.

Conclusion: Mass lesion of the middle frontal gyrus on the right is likely to represent a low-grade tumor. Differential diagnosis includes DNET, ganglioglioma, circumscribed astrocytoma and/or oligoastrocytoma. The features are not typical of a tumefactive plaque but this is not entirely excluded.

The patient underwent a stereotactic right frontal craniotomy and resection of the tumor.


MICROSCOPIC DESCRIPTION: Paraffin sections show a densely hypercellular glial tumor composed predominantly of pleomorphic oligodendroglial cells with a quantitatively smaller population of astrocytic cells. Numerous minigemistocytes and gliofibrillary oligodendrocytes are also present. Scattered mitotic figures are identified as well as foci of vascular endothelial cell hyperplasia. No necrosis is seen. Tumor is well demarcated from adjacent white matter. Perineuronal secondary structuring is prominent in adjacent cortex. An area of dystrophic calcification is present within the adjacent brain parenchyma. The features are of anaplastic oligoastrocytoma.

FINAL DIAGNOSIS: Anaplastic oligoastrocytoma WHO Grade III

Case Discussion

This case illustrates a tumor with imaging features suggesting a low-grade glioma that showed to be a high-grade tumor in the histology. 


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 recognized 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. 

Case courtesy of Associate Professor Pramit Phal

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