This sign has exhibited 100% specificity in some studies and up to 37% sensitivity in diagnosing adult-type diffuse astrocytoma with an IDH mutation.15, 16, 17Although the sign exhibits high specificity, false-positive “T2-FLAIR mismatch” findings have been reported, particularly in pediatric-type and glioneuronal tumors,18, 19making it an unreliable predictor of IDH status in the pediatric population. The gene discussed is IDH1; the disease is diffuse astrocytoma.