Oligodendroglioma Magnetic resonance imaging
The MRI appearances also vary depending on whether a histological diagnosis or a molecular definition is used.
Oligodendrogliomas NOS, or those tumors that histologically show oligodendroglial features but are 1p/19q intact show more homogeneous signal on T1 and T2 images and have sharper borders than 'true' oligodendroglioma, those with 1p/19q co-deletion. In fact, a lesion being well-circumscribed homogeneously T1 hypoattenuating with high T2 signal and T2/FLAIR mismatch without calcification is predictive of not having 1p19q codeletion 1)
Calcification and hemorrhage are difficult to distinguish on MR, appearing as areas of signal loss on T2* sequences, although the phase component of SWI may help. Peritumoral vasogenic edema is minimal in grade 2 tumors.
T1
Typically hypointense
T2
Typically hyperintense (except calcified areas)
T1 C+ (Gd)
Contrast enhancement is common but it is not a reliable indicator of tumor grade, with only 50% of oligodendrogliomas enhancing to a variable degree, and usually heterogeneously
Fewer than 20% enhance with gadolinium (compared to > 70% with grade III anaplastic ODG).
GRE/SWI
Calcium can be seen as areas of “blooming”
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 lower cellularity and greater hyaluronan proportion 2)
MR perfusion (PWI)
Iincreased vascularity “chicken wire” network of vascularity results in elevated relative cerebral blood volume (rCBV)
older literature 3) suggested that this was useful in predicting histological grade of tumor, however, how this relates to modern classification systems based on molecular markers is unclear