Imaging of oligodendroglioma

Abstract

Oligodendroglioma are glial tumours, predominantly occurring in adults. Their hallmark molecular feature is codeletion of the 1p and 19q chromosome arms, which is not only of diagnostic but also of prognostic and predictive relevance. On imaging, these tumours characteristically show calcification, and they have a cortical-subcortical location, most commonly in the frontal lobe. Owing to their superficial location, there may be focal thinning or remodelling of the overlying skull. In contrast to other low-grade gliomas, minimal to moderate enhancement is commonly seen and perfusion may be moderately increased. This complicates differentiation from high-grade, anaplastic oligodendroglioma, in which enhancement and increased perfusion are also common. New enhancement in a previously non-enhancing, untreated tumour, however, is suggestive of malignant transformation, as is high growth rate. MR spectroscopy may further aid in the differentiation between low- and high-grade oligodendroglioma. A relatively common feature of recurrent disease is leptomeningeal dissemination, but extraneural spread is rare. Tumours with the 1p/19q codeletion more commonly show heterogeneous signal intensity, particularly on T2 weighted imaging; calcifications; an indistinct margin; and mildly increased perfusion and metabolism than 1p/19q intact tumours. For the initial diagnosis of oligodendroglioma, MRI and CT are complementary; MRI is superior to CT in assessing tumour extent and cortical involvement, whereas CT is most sensitive to calcification. Advanced and functional imaging techniques may aid in grading and assessing the molecular genotype as well as in differentiating between tumour recurrence and radiation necrosis, but so far no unequivocal method or combination of methods is available.

Figure 1.

Transverse non-enhanced CT, T₁ weighted (T1w) and T₂ weighted (T2w) MRI sections, showing extensive, gyriform calcifications (arrows) on CT in the left frontal lobe. Note that the calcifications are only barely visible on T₁w images as discrete linear hyperintensities (arrows) and are not at all visible on T₂w imaging.

Figure 2.

Transverse T₂ weighted (T2w) MRI section showing hyperintensity and marked heterogeneity of signal in a left frontal lobe oligodendroglioma. Note extension of the lesion through the corpus callosum to the right frontal lobe (arrow), creating a “butterfly glioma” appearance.

Figure 3.

Transverse T₁ weighted (T1w) and contrast-enhanced T₁ weighted (cT1w) MRI sections, showing discrete, dot-like enhancement (arrow) in a right frontal lobe oligodendroglioma.

Figure 4.

Transverse CT, T₁ weighted (T1w) and contrast enhanced T₁ weighted (cT1w) MRI sections, showing course calcifications (arrows) in the right thalamus, which are hyperintense on the T₁w image and can easily be mistaken for contrast enhancement.

Figure 5.

Transverse (left) and coronal (right) T₂ fluid-attenuated inversion recovery MRI sections, showing hyperintensity and thickening of the cortex in a left frontal lobe oligodendroglioma.

Figure 6.

Transverse CT in bone window and T₂ weighted (T2w) MRI sections, showing remodelling of the skull's inner table (arrows) overlying a right frontal lobe oligodendroglioma.

Figure 7.

Transverse CT, T₂ weighted (T2w) and contrast enhanced T₁ weighted (cT1w) MRI sections, showing a left temporoparietal lobe anaplastic oligodendroglioma with calcification (CT: arrow), cystic degeneration (T2w: arrow), oedema (T2w: arrowheads) and ring-like enhancement (cT1w: arrow).

Figure 8.

Transverse contrast-enhanced T₁ weighted sections at the level of the medulla oblongata (a), fourth ventricle (b) and lateral ventricles (c), showing leptomeningeal seeding in recurrent anaplastic oligodendroglioma. Note the nodular enhancement surrounding the brain stem (a: arrows); lining the fourth ventricle (b: arrows) and along the cranial nerves in the right internal auditory canal (b: arrowhead); the ventricular wall (c: arrows) and the dura (c: arrowhead).

Figure 9.

Transverse T₂ weighted sections of (a) 1p/19q codeleted tumour and (b) 1p/19q intact tumour. Note the heterogeneous signal intensity, indistinct border and frontal lobar location in the codeleted tumour (a). By contrast, the intact tumour is more homogeneous, has a relatively sharp tumour border and is located in the temporoinsular region (b).