IDH1 and oligodendroglioma: The traditional histologic separation between astrocytomas and oligodendrogliomas is complemented by recent evidence for two molecularly and virtually exclusive subtypes, characterized by IDH, ATRX and TP53 mutation in the absence of 1p/19q codeletion (astrocytic) versus IDH mutation, 1p/19q codeletion, and TERT promoter mutation (oligodendroglial).