NIMG-21. IMPACT OF GENETIC ALTERATIONS ON TUMOR LOCATIONS AND LESION HETEROGENEITY FOR WHO GRADE 2 AND 3 GLIOMAS: A VOXEL-BASED LESION MAPPING AND IMAGE TEXTURE ANALYSIS OF 201 GLIOMAS

Genetic alterations found in WHO grade 2 and 3 gliomas include IDH1/2 and TERT promoter mutations and 1p19q co-deletion, which alterations are known to have great impact on the prognosis of the patient. In this research, the authors attempted to test the hypothesis that genetic alterations could contribute to the locations and heterogeneity of the tumor by analyzing 201 WHO grade 2 and 3 gliomas using voxel-based lesion mapping (VLM) and image texture analysis. All T2-hyperintese lesions were normalized and mapped on the standard MRI atlas (MNI152) using normalized mutual information algorithm. In addition, image texture, that is the heterogeneity of the lesion on T2-weighted images, were evaluated by calculating the entropy of the lesion. Higher entropy is known to correspond to more heterogenous texture of the image and vice versa. 201 cases were divided into 3 groups according to the genetic alterations; 67 cases for IDH1/2 and TERT promoter mutated (IDHmt/TERTmt), 61 cases for IDH1/2 mutated but TERT promoter wild-type (IDHmt/TERTwt) and 73 cases for IDH1/2 wild-type gliomas (IDHwt). VLM revealed that IDHmt tumors tended to reside involving the cortex of the brain involving frontal, insular and temporal cortexes, while IDHwt tumors located closer to the center of the brain. IDHmt/TERTmt tumors were found to involve the frontal lobe 18% more than IDHmt/TERTwt tumors, while the temporal lobe being 20% less. Image texture analysis showed that entropies of T2-hyperintese lesions were 6.31 ± 0.47, 6.39 ± 0.42 and 6.05 ± 0.54 respectively for IDHmt/TERTmt, IDHmt/TERTwt and IDHwt tumors with IDHwt tumors being statistically significantly lower than the other two types of tumors (one-way ANOVA and Tukey’s Comparison Test). These results confirm that genetic alterations of glioma do affect locations and heterogeneity of the lesion.