Oligodendroglioma

Oligodendrogliomas represent 15-20% of the intracranial gliomas and 5-10% of all the intracranial neoplasms. They are more common than astrocytomas. These tumours occur principally in the supratentorial white matter. They then infilterate along the white matter tracts in a non destructive manner. They may also invade the adjacent cortex. Involvement of deep structures is also common. Approximately 85% on them occur in cerebral hemispheres,and more than half in frontal lobes. Peak age of incidence is in fourth and fifth decades of life. They grow very slowly and Initial clinical presentation is most often a seizure if not headache. Oligodendrogliomas contain multiple irregular masses of dystrophic calcification, Areas of cystic degeneration are found in 20% of cases, mainly in larger tumours. Intratumoral haemorrhage is a frequent finding. On CT, Oligodendrogliomas most often appear as masses of heterogenous density in the frontal lobe with irregular and poorly defined margins involving the more superficial white matter and infilterating into the overlying cortex and obscuring the gray-white interface. The characteristic feature is the presence of large irregular calcifications (70-90%), sometimes described as ribbonlike or gyriform in character, within the tumor. Intratumoral cyst formation is common (20%), but frank intratumoral necrosis is unusual and indicates poor prognosis. Contrast enhancement is noted in approximately two thirds of oligodendrogliomas. On MRI, oligodendrogliomas appear heterogenous on both T1 and T2 weighted spin echo images, because of the presence of intratumoral cysts and calcifications. Peritumoral oedema is noted in about a third of cases. Erosion of overlying calvaria may be identified on both CT and MRI when the lesion is peripheral.