Increased intratumoral infiltration in IDH wild-type lower-grade gliomas observed with diffusion tensor imaging

Diffuse lower grade gliomas (LGG) with isocitrate dehydrogenase (IDH) gene mutations (IDH_MUT) have a distinct survival advantage compared with IDH wild-type (IDH_WT) cases but the mechanism underlying this disparity is not well understood. Diffusion Tensor Imaging (DTI) has identified infiltrated non-enhancing tumor regions that are characterized by low isotropic (p) and high anisotropic (q) diffusion tensor components that associate with poor survival in glioblastoma. We hypothesized that similar regions are more prevalent in IDH_WT (vs. IDH_MUT) LGG.

p and q maps were reconstructed from preoperative DTI scans in N = 41 LGG patients with known IDH mutation and 1p/19q codeletion status. Enhancing and non-enhancing tumor volumes were autosegmented from standard (non-DTI) MRI scans. Percentage non-enhancing tumor volumes exhibiting low p and high q (V_inf) were then determined using threshold values (p = 2 × 10^-3mm²/s, q = 3 × 10^-4 mm²/s) and compared between IDH_WT and IDH_MUT LGG, and between IDH_MUT LGG with and without 1p/19q codeletion.

V_inf volumes were significantly larger in IDH_WT LGG than in IDH_MUT LGG (35.4 ± 18.3% vs. 15.9 ± 7.6%, P < 0.001). V_inf volumes did not significantly differ between IDH_MUT LGG with and without 1p/19q codeletion (17.1 ± 9.5% vs. 14.8 ± 5.8%, P = 1.0).

IDH_WT LGG exhibited larger volumes with suppressed isotropic diffusion (p) and high anisotropic diffusion (q) which reflects regions with increased cell density but non-disrupted neuronal structures. This may indicate a greater prevalence of infiltrative tumor in IDH_WT LGG.