Anaplastic Oligodendroglioma (AO)

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Definition

AO is an oligodendroglioma with focal or diffuse features of malignancy. AO is a WHO Grade III glioma.

Epidemiology

AO is thought to account for 20-50% of all oligodendroglial tumors. The majority of these lesions arise in adults with a mean age at operation of 48.7 years. The is a slight male predominance (1.5:1).

Localization

Like oligodendrogliomas, AO typically occurs in the cortex and white matter of the cerebral hemispheres, most commonly in the frontal lobe.

Clinical presentation

Many patients present with a long history of seizures or headache, though the time course of symptoms tends to shorter and the progression of symptoms faster than in patients who present with oligodendroglioma.

Imaging

MRI demonstrates a heterogeneous lesion with irregularly scattered regions of necrosis, cystic degeneration, intratumoral hemorrhage, and calcification.

Macroscopy

AO may appear similar to an oligodendroglioma, though with regions of overt tumor necrosis.

Histopathology

AO is a composed of neoplastic oligodendrocytes with histological features of malignancy, including increased cellularity, marked cytological atypia, and high mitotic activity. Microvascular proliferation and necrosis may be present.

Molecular genetics

In addition to the molecular changes seen in oligodendrogliomas, AOs commonly possess deletions in CDKN2A AND CDKN2C, as well as amplification of CDK4, EGFR, VEGF, and the myc oncogene.

Prognosis

Mean survival time following medical and surgical intervention is 3-4 years, with 5- and 10-year survival rates of 41% and 20%, respectively. Risk of malignant progression is thought to correspond to the astrocytic component of the tumor. Factors though to confer more favorable outcome include young age, chromosomes 1p and 19q deletion, frontal location, gross total surgical resection, and post-operative Karnofsky score.