WHO classification of CNS tumours

The WHO classification of CNS tumours is the most widely accepted system for classifying CNS tumours and was based on the histological characteristics of the tumour. 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. "At this point, a decision to undertake the 5th edition series of WHO Blue Books has not been made" 3. 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.  

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

The most recent update (2016) has significantly changed the classification of a number of tumour 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 tumours of the dura with hemangiopericytoma, which although appearing very different on imaging seem now to be manifestations of the same tumour. 

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

For entities that now incorporate molecular markers into their definition (e.g. oligodendroglioma IDH-mutant, 1p19q co-deleted) it is recognised 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 behaviour, not WHO Grade
  • *: refers to a 'new' tumour in the classification
  • italics: refers to a provisional inclusion
Diffuse astrocytic and oligodendroglial tumours
Other astrocytic tumours
Ependymal tumours
Other gliomas
Choroid plexus tumours
Neuronal and mixed neuronal-glial tumours
Tumours of the pineal region
Embryonal tumours
Tumours of cranial and paraspinal nerves
Tumours of meningothelial cells
Mesenchymal, non-meningothelial tumours
Melanocytic lesions
Lymphomas
Histiocytic tumours
Germ cell tumours
Tumours of the sellar region

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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rID: 2277
Tag: cases
Synonyms or Alternate Spellings:
  • WHO classification of CNS tumours
  • CNS tumours (WHO classification)

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