Neuroimaging plays a critical role in the management of patients with gliomas. While conventional magnetic resonance imaging (MRI) remains the standard imaging modality, it is frequently insufficient to inform clinical decision‐making. There is a need for noninvasive strategies for reliably distinguishing low‐grade from high‐grade gliomas, identifying important molecular features of glioma, choosing an appropriate target for biopsy, delineating target area for surgery or radiosurgery, and distinguishing tumor progression (TP) from pseudoprogression (PsP). One recent advance is the identification of the T2/fluid‐attenuated inversion recovery mismatch sign on standard MRI to identify isocitrate dehydrogenase mutant astrocytomas. However, to meet other challenges, neuro‐oncologists are increasingly turning to advanced imaging modalities. Diffusion‐weighted imaging modalities including diffusion tensor imaging and diffusion kurtosis imaging can be helpful in delineating tumor margins and better visualization of tissue architecture. Perfusion imaging including dynamic contrast‐enhanced MRI using gadolinium or ferumoxytol contrast agents can be helpful for grading as well as distinguishing TP from PsP. Positron emission tomography is useful for measuring tumor metabolism, which correlates with grade and can distinguish TP/PsP in the right setting. Magnetic resonance spectroscopy can identify tissue by its chemical composition, can distinguish TP/PsP, and can identify molecular features like 2‐hydroxyglutarate. Finally, amide proton transfer imaging measures intracellular protein content, which can be used to identify tumor grade/progression and distinguish TP/PsP.

Objective:To assess the predictive value of T2 appearance as a defining criterion of T2-FLAIR mismatch sign (T2FM), further characterize tumors which display the marker, and describe its radiographic evolution.Methods:Records from 64 patients with astrocytomas were assessed for age at diagnosis, sex, tumor characteristics on pre-treatment CT, MRI, and pathology, documentation of T2FM, treatment course, and temporal changes in tumor appearance. Cases were divided into those meeting “classic” criteria (homogenous T2, hyperintense FLAIR rim), those considered “geographic” (heterogeneous T2, hyperintense FLAIR rim), and those which were negative (no FLAIR rim). Groups were compared using Chi square, estimate of effect, and qualitative analyses.Results:Including “geographic” tumors increased T2FM sensitivity 30% among astrocytomas without decreased specificity for IDH mutation. Tumors with T2FM characteristics were more cystic, less enhancing, and affected younger patients. T2FM persisted in residual tumors following subtotal resection and disappeared with radiotherapy, persisted in 5/8 recurrent tumors which were originally T2FM positive, and was identified in tumors with high grade characteristics. T2FM was able to predict IDH mutation status on sequencing when antibody testing was negative.Conclusions:The presence of a hyperintense FLAIR rim, regardless of T2 appearance, is a reliable indicator of IDH mutation among astrocytomas. Tumors with a FLAIR rim are more cystic and this may lend to their characteristic appearance on MRI. T2FM demonstrates distinctive temporal radiographic changes, may be seen in high grade gliomas, and may be used in combination with other variables to strengthen prediction of IDH status.