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WHO classification of CNS tumors

Assoc Prof Frank Gaillard ◉ ◈ et al.

The WHO classification of CNS tumors is the most widely accepted system for classifying CNS tumors and was based on the histological characteristics of the tumor. Although the most recent version of the 'blue book' is the 4th edition from 2007, an update has been released in 2016 3, which should be considered a replacement for the earlier version.

This 2016 update has, for the first time, included molecular parameters into the diagnostic schema, and in fact, has elevated them in some instances above histological features 3.  

The 5th edition should become available towards the end of 2020 and incorporates some important changes to diffuse gliomas and glioblastoma as outlined in cIMPACT recommendations for the classification of diffuse gliomas 2020 6

This is a fairly dry article, primarily for reference. For more readable versions, see the article on brain tumors and brain tumors in infancy for general discussion of these topics.

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The most recent update (2016) has significantly changed the classification of a number of tumor families, introducing a greater reliance on molecular markers. The most notable changes involve diffuse gliomas, in which IDH status (mutated vs. wildtype) and 1p19q co-deletion (for oligodendrogliomas) have risen to prominence. Importantly if histological phenotype and genotype are not-concordant (e.g. looks like diffuse astrocytoma but is 1p19q co-deleted, ATRX-wildtype) then genotype wins, and it is used to determine diagnosis 3. 

Medulloblastomas have also been divided into distinct molecular subgroups. 

Another change is the combining of solitary fibrous tumors of the dura with hemangiopericytoma, which although appearing very different on imaging seem now to be manifestations of the same tumor. 

Despite a move towards molecular markers for some entities, the classification continues to be organized according to the cell of origin (e.g. ependymal tumors) or anatomical origin (e.g. tumors of the sellar region). 

For entities that now incorporate molecular markers into their definition (e.g. oligodendroglioma IDH-mutant, 1p19q co-deleted) it is recognized that such markers are not always available or identified. In such cases, a 'not otherwise specified (NOS)' option is available (e.g. oligodendroglioma NOS). 

  • NOS: not otherwise specified 
  • four digit code: is from the International Classification of Disease for Oncology (ICD-O)
  • /: the number after the slash (/) refers to biological behavior, not WHO Grade
  • *: refers to a 'new' tumor in the classification
  • italics: refers to a provisional inclusion

The following entities are no longer found in the 2016 WHO classification, last seen in the 2007 version. 

Although oligoastrocytomas remain entities, they are now going to be rare, requiring molecularly distinct populations of both components: astrocytes (IDH-mutant, ATRX-mutant, 1p19q-intact) and oligodendroglial cells (IDH-mutant, ATRX-wildtype, 1p19q-co-deleted) 3. 

The following entities have been introduced in the 2016 WHO classification.

. 

Astrocytic tumour
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Article information

rID: 2277
System: Central Nervous System, Spine
Section: Classifications
Tag: cases, cases, cases, cases
Synonyms or Alternate Spellings:
  • WHO classification of CNS tumours
  • CNS tumours (WHO classification)

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