Patient presented with headaches and seizures.
There is a mass lesion that is hypointense on the T1W images in the left fronto-temporal region. It is heterogeneously hypointense on the T2W images with cystic and solid components. Hyperintense areas on the T1W images were seen to represent calcium on the CT scan (images not available). There is enhancement of the periphery and of the solid component of this lesion. Perilesional edema is noted with resultant mass effect.
Oligodendrogliomas occur as frequently as well-differentiated diffuse astrocytomas, usually in the fourth to fifth decades. They represent 2% to 5% of all primary intracranial tumors and 5% of all gliomas. They are usually located in the frontal and fronto-temporal regions. However, a few are seen in the ventricular walls, cerebellum, and very rarely within the spinal cord. The prognosis is better than that of infiltrative astrocytomas of similar histologic grade. The progression of oligodendrogliomas to more anaplastic types occurs as it does in diffuse astrocytomas, but it evolves over longer periods of time. Treatment has centered around surgical excision, but these lesions are infiltrative and therefore are generally not cured by surgery alone. Response to chemotherapy may be good.
Pathology: |
Oligodendrogliomas are solid, infiltrative lesions with poorly defined borders, like infiltrative astrocytomas. They often contain cellular elements of other glial types, so are considered "mixed" in up to one-half of cases. These lesions are densely cellular with only minimal acellular stroma (composed of uniform cells with a halo like appearance, giving rise to the term fried-egg appearance). The lesions classically exhibit extensive infiltration of cortex. Focal cystic necrosis and intratumoral hemorrhage are frequent findings. Calcification is extremely common, being associated with the walls of intrinsic blood vessels. It may be within the tumor tissue or separate in the surrounding brain parenchyma, especially in the cortical gray matter.
On MRI: |
Imaging studies of these lesions are very useful and can often suggest the specific diagnosis, based on the location, the presence of characteristic calcification and the occasional finding of overlying calvarial change (scalloping and thinning of the inner table of the skull caused by tumor expansion of the cerebral cortex) suggestive of a relatively long-standing mass lesion. They are usually heterogeneous, but relatively low intensity (near isointense to gray matter) on T2W images. Small cystic/necrotic areas and hemorrhage are commonly found within these masses. The calcification pattern can be dense, linear, nodular or gyriform. On MRI the areas of calcification appear as low signal intensity on T2W images (calcification on CT has been reported in 50% to 90% of oligodendrogliomas). Iron is often deposited concomitantly with dystrophic calcification. The extremely heterogeneous appearance of oligodendrogliomas, even on spin-echo images, can be at least in part a reflection of tumoral calcification. Edema is not usually a significant feature of lower grade oligodendrogliomas. Contrast enhancement has been seen in about one-half of cases.
Differential Diagnosis:
Astrocytoma
Astrocytomas are more homogeneous, not as frequently calcified and are
deeper in the hemisphere.
Glioblastoma
Glioblastomas are often quite heterogeneous and as in malignant
oligodendroglioma with extensive surrounding high intensity "edema", can be
identical in appearance.
Dysembryoplastic neuroepithelial tumor (DNET)
Can be identical to oligodendroglioma, particularly when there is no
significant edema.
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