Conventional MRI features can predict the molecular subtype of adult grade 2-3 intracranial diffuse gliomas

Molecular biomarkers are important for classifying intracranial gliomas, prompting research into correlating imaging with genotype ("radiogenomics"). A limitation of the existing radiogenomics literature is the paucity of studies specifically characterizing grade 2-3 gliomas into the three key molecular subtypes. Our study investigated the accuracy of multiple different conventional MRI features for genotype prediction.

Grade 2-3 gliomas diagnosed between 2007 and 2013 were identified. Two neuroradiologists independently assessed nine conventional MRI features. Features with better inter-observer agreement (κ ≥ 0.6) proceeded to consensus assessment. MRI features were correlated with genotype, classified as IDH-mutant and 1p/19q-codeleted (IDH^mut/1p19q^codel), IDH-mutant and 1p/19q-intact (IDH^mut/1p19q^int), or IDH-wildtype (IDH^wt). For IDH^wt tumors, additional molecular markers of glioblastoma were noted.

One hundred nineteen patients were included. T2-FLAIR mismatch (stratified as > 50%, 25-50%, or < 25%) was the most predictive feature across genotypes (p < 0.001). All 30 tumors with > 50% mismatch were IDH^mut/1p19q^int, and all seven with 25-50% mismatch. Well-defined margins correlated with IDH^mut/1p19q^int status on univariate analysis (p < 0.001), but this related to correlation with T2-FLAIR mismatch; there was no longer an association when considering only tumors with < 25% mismatch (p = 0.386). Enhancement (p = 0.001), necrosis (p = 0.002), and hemorrhage (p = 0.027) correlated with IDH^wt status (especially "molecular glioblastoma"). Calcification correlated with IDH^mut/1p19q^codel status (p = 0.003). A simple, step-wise algorithm incorporating these features, when present, correctly predicted genotype with a positive predictive value 91.8%.

T2-FLAIR mismatch strongly predicts IDH^mut/1p19q^int even with a lower threshold of ≥ 25% mismatch and outweighs other features. Secondary features include enhancement, necrosis and hemorrhage (predicting IDH^wt, especially "molecular glioblastoma"), and calcification (predicting IDH^mut/1p19q^codel).