Revision 54 for 'Oligodendroglioma'
An oligodendroglioma accounts for 5 - 25% of all gliomas and 5 - 10% of all primary intracranial neoplasms.
Demographics and clinical presentation
These are usually tumours of middle-aged adults, occurring most commonly in the 4th and 5th decades of life.
Due to their usual cortical involvement, presentation is most frequently as a result of seizures.
Tumours are typically located in supratentorially (85%), involving the white matter and overlying cortex. They are most commonly found in the frontal lobes.
Pathology & Classification
Generally, oligodendrogliomas are well-circumscribed, gelatinous, gray masses. They are usually calcified (70 - 90% : once of most frequently calcifying tumours), less often with focal haemorrhage. 20% of these tumours are cystic, and they can often expand a gyrus and remodel the skull. They can occur essentially anywhere, including intraventricularly where they are difficult to distinguish from central neurocytomas on light microscopy.
Microscopic Appearance and Classification
Oligodendroglioma (WHO grade II/IV)
Sheets of regular cells with spherical nuclei containing finely granular chromatin surrounded by a halo of cytoplasm. Typically contains a delicate network of anastomosing capillaries giving it a so called 'chicken wire' appearance 6. These tumours are slowly growing.
Anaplastic oligodendroglioma (WHO grade III/IV)
Increased cellular density, mitotic activity, microvascular proliferation and necrosis. Nuclear anaplasia is also common.
Anaplastic oligodendrogliomas make up 20 - 50% of all oligdendrogliomas. When necrosis is present in an anaplastic oligodendroglioma then they are considered WHO Grade IV lesions and referred to a GBM with oligodendroglioma component.
Oligoastrocytomas, a tumour of mixed oligodendroglioma and astrocyoma cell populations are common, and carry a prognosis equivalent to their astrocytoma component. (worse grade for grade).
Molecular genetics and sub classification
- 1p/19q chromosome loss : excellent response to radiation and chemotherapy.
- 1p/19q chromosome intact : refractory to radiation and chemotherapy 2.
Non contrast CT
Tumours are of mixed density (hypodense to isodense). High-attenuation areas within the tumour are likely from calcification (70 - 90% of oligodendrogliomas are calcified) or, less commonly, haemorrhage. Calcification can be located centrally, peripherally or they can be ribbon-like 4. The overlying skull may show pressure erosion.
Post contrast CT
50% of oligodendrogliomas enhance. Degree of enhancement is extremely variable (no enhancement to striking)
Tumours in which 1p/19q is intact show more homogenous signal on T1 and T2 images and have sharper borders than tumours with 1p/19q deletions. Calcification and haemorrhage are difficult to distinguish on MR. Peri tumoural vasogenic oedema is minimal.
- T1 : typically hypo intense
- T2 : typically hyper intense (except calcific areas)
- T2* : calcium seen as areas of "blooming."
- C+ (GAD) : contrast enhancement is common but it is not a reliable indicator of tumour grade, with only 50% of oligodendrogliomas enhancing to a variable degree, and usually heterogenously.
- DWI : typically no diffusion restriction. DWI can be used to help differentiate oligodendrogliomas (generally lower grade) from astrocytomas (generally higher grade); astrocytomas have higher ADC values probably because of their higher cellularity 5.
- MR Perfusion : increased vascularity results in elevated relative cerebral blood volume (rCBV) of grade II vs grade III on PWI; PWI has a sensitivity of 95% and PPV or 87% for distinguishing grade II from grade III Oligodendrogliomas 1; a threshold of 1.75, rCBV above this threshold demonstrate more rapid tumour progression 1.
11C-Methionine studies can be used to differentiate oligdendrogliomas from anaplastic oligodendrogliomas. FDG uptake of oligodendrogliomas is similar to normal white matter. FDG uptake of anaplastic oligodendrogliomas is similar to normal gray matter.
Treatment and Prognosis
Treatment is surgical, with adjuvant radiotherapy and chemotherapy. Although they are macroscopically well delineated, infiltration is present at their margins and local recurrence is common. 5 year survival rate ranges around 50 - 75%.