IDH1 and oligodendroglioma: T2-FLAIR mismatch sign was found in 10 (45%) out of 22 patients with IDH-mutant astrocytomas, whereas it was found in 1 (5%) out of 20 patients with oligodendrogliomas and 1 (5%) out of 22 patients with IDH-wild-type astrocytomas (Table 1).