Classification and pathologic diagnosis of gliomas
- David N Louis, MD
David N Louis, MD
- Massachusetts General Hospital
- Benjamin Castleman Professor of Pathology
- Harvard Medical School
- David Schiff, MD
David Schiff, MD
- Professor of Neurology, Neurological Surgery, and Medicine
- University of Virginia School of Medicine
- Tracy Batchelor, MD, MPH
Tracy Batchelor, MD, MPH
- Giovanni Armenise Professor of Neurology
- Harvard Medical School
- Section Editors
- Jay S Loeffler, MD
Jay S Loeffler, MD
- Section Editor — Neurooncology
- Professor of Radiation Oncology
- Harvard Medical School
- Patrick Y Wen, MD
Patrick Y Wen, MD
- Section Editor — Neurooncology
- Professor of Neurology
- Harvard Medical School
Gliomas account for the great majority of primary tumors that arise within the brain parenchyma. The term "glioma" refers to tumors that have histologic features similar to normal glial cells (ie, astrocytes, oligodendrocytes, and ependymal cells). For each of these types of gliomas, there are neoplasms that span a broad spectrum of biological aggressiveness.
Historically, the slower growing lesions, corresponding to World Health Organization (WHO) grades I and II, have been commonly referred to as low-grade gliomas, while the more rapidly progressive tumors are referred to as high-grade gliomas. The WHO classification recommends avoiding the term "low-grade glioma," however, since it lumps together a heterogenous groups of tumors, many of which have significantly different biological properties, prognoses, and treatment approaches [1,2]. Among grade I and grade II gliomas, for example, current classification favors a distinction between diffuse gliomas (eg, grade II diffuse astrocytoma and oligodendroglioma) and more circumscribed astrocytic tumors (eg, grade I pilocytic astrocytoma).
The classification and diagnosis of gliomas will be reviewed here. Pathogenesis of diffuse gliomas is reviewed separately. (See "Molecular pathogenesis of diffuse gliomas".)
HISTORY OF GLIOMA CLASSIFICATION
The classification and grading of gliomas has evolved over time, beginning in 1926 with a system devised by Bailey and Cushing  and later revised by Kernohan, Ringertz, and others [4-6]. Modern classification of gliomas is based on the World Health Organization (WHO) Classification of Central Nervous System Tumors, first published in 1979 and revised four times since then, most recently in 2016 [1,2].
As of the 2016 edition of the WHO classification, gliomas are classified based not only on histopathologic appearance but also on well-established molecular parameters . The incorporation of molecular features has most notably impacted the classification of astrocytic and oligodendroglial tumors, which are now grouped together as diffuse gliomas, on the basis of growth pattern, behavior, and shared isocitrate dehydrogenase (IDH) genetic status.
- WHO Classification of Tumours of the Central Nervous System, Revised 4th Edition, Louis DN, Ohgaki H, Wiestler OD, Cavenee WK (Eds), IARC, Lyon 2016.
- Louis DN, Perry A, Reifenberger G, et al. The 2016 World Health Organization Classification of Tumors of the Central Nervous System: a summary. Acta Neuropathol 2016; 131:803.
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- HISTORY OF GLIOMA CLASSIFICATION
- KEY MOLECULAR DIAGNOSTIC TESTS
- IDH1/IDH2 mutations
- 1p/19q co-deletion
- ATRX mutation
- TP53 mutation
- H3 K27M mutation
- BRAF alterations
- RELA fusion
- HISTOPATHOLOGIC AND MOLECULAR CLASSIFICATION
- Diffuse astrocytic and oligodendroglial tumors
- - General features
- - IDH-mutant astrocytomas
- - IDH-wildtype astrocytomas and glioblastoma
- - IDH-mutant, 1p/19q-codeleted oligodendrogliomas
- - NOS designation
- Oligoastrocytomas NOS
- Other astrocytic tumors
- - Pilocytic astrocytoma
- - Pleomorphic xanthoastrocytoma
- - Subependymal giant cell astrocytoma
- Ependymal tumors
- Neuronal and mixed neuronal-glial tumors
- INFORMATION FOR PATIENTS