Imaging diagnosis of adult-type diffuse gliomas in the era of WHO CNS5 and cIMPACT-NOW updates 8–11: a narrative review

Abstract The 2021 World Health Organization Classification of Tumours of the Central Nervous System, 5th edition (WHO CNS5) reorganized adult-type diffuse gliomas into three integrated tumor types—astrocytoma, IDH-mutant (AST); oligodendroglioma, IDH-mutant and 1p/19q-codeleted (ODG); and glioblastoma, IDH-wildtype (GBM)—and introduced molecular criteria that allow histologically lower-grade IDH-wildtype astrocytic tumors to be diagnosed as GBM (so-called “molecular” GBM). Although molecular genetic information has become central to glioma diagnosis, preoperative imaging-based prediction of tumor type remains essential for guiding surgical strategy, the choice between maximal safe resection and diagnostic biopsy, and treatment planning before final integrated diagnosis. The recent INDIGO trial, which demonstrated efficacy of the IDH1/2 inhibitor vorasidenib in residual grade 2 IDH-mutant glioma, has further increased the importance of preoperative imaging assessment of IDH mutation status. This mini-review summarizes the current role of imaging in adult-type diffuse gliomas in the WHO CNS5 era. First, we review imaging differentiation between AST and ODG, including the T2-fluid-attenuated inversion recovery (FLAIR) mismatch sign and its partial form, classic features supporting ODG such as coarse calcification and cortical-subcortical location, and newer biomarkers including the cortical high-flow sign on arterial spin labeling, subcortical FLAIR signal drop, and 1 H-MR spectroscopy findings such as 2-hydroxyglutarate and cystathionine. Second, we describe imaging features of “molecular” GBM, including its frequently infiltrative, poorly enhancing appearance and longitudinal histologic grade progression. Third, we discuss the implications of cIMPACT-NOW Updates 8–11 for neuroradiologic diagnosis. In the WHO CNS5 era, imaging plays a central role in supporting integrated diagnosis and prioritizing appropriate molecular testing.