Perfusion, diffusion, and anatomical MRI characteristics of pathologically-confirmed malignant transformation in IDH-mutant gliomas.

Background: This study explored MRI characteristics at the time of tumor progression to study pathologically-confirmed MT in IDHm 1p/19q-intact astrocytomas (IDHm-A) and IDHm 1p/19q-co-deleted oligodendrogliomas (IDHm-O).

Methods: N=64 patients with initial pathological grade 2 IDH-mutant glioma diagnosis who underwent repeated tissue sampling and were classified as pathologically-confirmed MT (n=35) or non-MT (n=29) with available pre-surgical anatomical (n=64), diffusion-weighted (n=61), and dynamic susceptibility contrast perfusion MRI (n=53) were retrospectively studied. Measurable contrast enhancement (>1000mm3), tumor volume, tumor growth rate, sphericity, median apparent diffusion coefficient (ADC), and normalized relative cerebral blood volume (nrCBV) were compared between MT vs. non-MT IDHm-A and IDHm-O.

Results: 81% of contrast-enhancing IDHm-A and 100% of contrast-enhancing IDHm-O demonstrated MT, while 41% of IDHm-A and 62% IDHm-O exhibited both non-enhancing tumor progression and MT. Tumor volumes were significantly larger in patients with MT compared to non-MT groups for IDHm-A (P=0.02) and IDHm-O (P=0.04). T2/FLAIR tumor volume growth rate was significantly higher (P=0.003), nrCBV was significantly higher (P=0.002), and ADC trended lower (P=0.06) in MT vs. non-MT IDHm-A. There were no significant differences in growth rate, ADC, nrCBV, or sphericity when comparing MT vs. non-MT IDHm-O (P>0.05).

Conclusions: Many MT IDHm gliomas remain non-enhancing. Growth rate, diffusion, and perfusion MRI show differences between MT and non-MT in IDHm-A but not IDHm-O, which may reflect the different tumor biology of these IDHm molecular subtypes and their need for separate imaging biomarkers. Tumor volumes can help determine MT for both IDHm-A and IDHm-O.