In IDH mutant astrocytomas WHO grade 4 with homozygous deletions of CDKN2A/B, histological findings, such as microvascular proliferation and tumor necrosis can be absent with the consequence that they radiologically show no contrast enhancement, no edema, and no necrosis and are therefore easily misinterpreted as low-grade gliomas. The gene discussed is CDKN2A; the disease is astrocytoma (excluding glioblastoma).