OLIG2 and extraventricular neurocytoma: For this reason, the immunohistochemistry of Synaptophysin should be supplemented with immunohistochemistry for OLIG2 (expression of this marker is usually incompatible with EVN) and molecular investigations to look for IDH mutations (in EVN, IDH must be non-mutated) and/or to look for co-deletion of chromosomes 1p and 19q (AVN must be 1p/19q non-codeleted).3