Anaplastic oligodendroglioma is a WHO grade III diffuse infiltrating glioma that has histological features of anaplasia, and molecular markers consistent with an oligodendroglioma (1p19q co-deletion and IDH mutation) as per the current (2016) WHO classification of CNS tumours 1. They make up 20-50% of all oligodendrogliomas. If the molecular status is unavailable then the diagnosis relies on histology alone and is given the designation anaplastic oligodendroglioma NOS.
Anaplastic oligodendrogliomas tend to present in a slightly older age group than WHO grade II tumour, presumably on account of them having been undiagnosed for some time.
Clinical presentation is non-specific with symptoms related to increased intracranial pressure and focal neurological deficits being common. Seizures are also fairly common, but not as common as with WHO grade II oligodendrogliomas 1.
Anaplastic oligodendrogliomas demonstrate increased cellular density, increased mitotic activity, microvascular proliferation and necrosis. Nuclear anaplasia is also common.
Importantly, and unlike astrocytomas, oligodendrogliomas with necrosis and microvascular proliferation are considered only WHO grade III anaplastic oligodendrogliomas and not WHO grade IV glioblastomas 1. In other words, if you have a tumour that is both IDH mutated and 1p19q co-deleted you can never call it a glioblastoma. Having said that occasionally IDH wild-type glioblastomas may have 1p19q deletions.
The radiographic features of anaplastic oligodendrogliomas are highly variable and range from those of oligodendrogliomas to glioblastomas. Generally, they demonstrate more intense contrast enhancement and more heterogeneity than lower grade tumours 1.
Treatment and prognosis
Prognosis with maximal surgical and medical management is significantly poorer than WHO grade II oligodendrogliomas but better than anaplastic astrocytomas 1. Again, the recent change in classification makes interpretation of survival data difficult, given most of it does not report molecular markers.
- 1. Louis DN, Ohgaki H, Wiestler OD, Cavenee WK "WHO Classification of Tumours of the Central Nervous System. 4th Edition Revised" ISBN: 9789283244929