IDH1 and astrocytoma (excluding glioblastoma): The T2-FLAIR mismatch sign was originally described in 2017 and strongly correlated with the diagnosis of IDH mutant 1p19q non-codeleted gliomas (astrocytomas).2 The sign included two observations from standard magnetic resonance imaging (MRI): (1) complete or near-complete and almost homogeneous hyperintense signal on T2-weighted images, with (2).