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  • Updated 06.15.2020
  • Released 06.15.2020
  • Expires For CME 06.15.2023

Low-grade gliomas

Introduction

Overview

Low-grade gliomas consist of WHO grade II primary CNS tumors with a glial lineage. These tumors, often described as “diffuse” and/or “infiltrating” typically present with seizures in otherwise healthy young adults. Low-grade gliomas have a better prognosis than anaplastic gliomas and advances in understanding of tumor genetics have reconfigured classification, improved prognostication, and helped identify patients who may respond more effectively to therapies. The authors summarize the basic biology, clinical features, and evolving treatment options for patients with low-grade gliomas.

Key points

• Low-grade gliomas account for approximately 15% of glial tumors in adults.

• Most patients present with seizures, often with a history of focal seizures persisting for weeks or months.

• Tumor genetics and molecular pathology are now a pillar of the most recent WHO classification.

• Common practice is maximal safe resection. Other treatment options include radiation therapy, chemotherapy, or deferred intervention.

Historical note and terminology

This article will focus on WHO grade II CNS tumors of primary glial origin, specifically infiltrating gliomas. Under the current WHO classification scheme, this includes diffuse astrocytoma (IDH-mutant, IDH-wild type, and NOS), oligodendroglioma (IDH mutant and 1p/19q co-deleted, and NOS), and oligoastrocytoma NOS (23). Other “low-grade” tumors with glial elements, such as pilocytic astrocytoma (WHO grade I), as well as tumors with mixed glial/neuronal elements, including ganglioglioma, dysembryoblastic neuroepithelial tumor, and central neurocytoma, are separate entities and are not discussed here.

The current WHO 2016 classification requires demonstration of IDH1 or IDH2 mutation status for low-grade gliomas of all histologic subtypes as well as demonstration of 1p/19q codeletion status for oligodendroglial histologic subtypes. Notably, the WHO classification discourages the diagnosis of tumors as oligoastrocytoma or “mixed glioma”, although the entity of oligoastrocytoma NOS is still described in detail. These declarations are new from the 2007 WHO classification, and represent a nosological “reshuffling” of certain glioma patients, both low- and high-grade. In clinical practice, this has translated into a relative blurring of previously hardened delineations between oligodendroglial, astrocytic, and mixed histologic subtypes.

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