2016 WHO Classification Brain Tumours

WHO brain tumour classification has been updated in 2016. The 2016 World Health Organization Classification of Tumors of the Central Nervous System is both a conceptual and practical advance over its 2007 predecessor. For the first time, the WHO classification of CNS tumors uses molecular parameters in addition to histology to define many tumor entities, thus formulating a concept for how CNS tumor diagnoses should be structured in the molecular era. 

• 2016 CNS WHO presents major restructuring of the diffuse gliomas, medulloblastomas and other embryonal tumors, and incorporates new entities that are defined by both histology and molecular features, including glioblastoma, IDH-wildtype and glioblastoma, IDH-mutant; diffuse midline glioma, H3 K27M–mutant; RELA fusion–positive ependymoma; medulloblastoma, WNT-activated and medulloblastoma, SHH-activated; and embryonal tumour with multilayered rosettes, C19MC-altered. 

For Full reading of the classification and reference for these notes: 

Acta Neuropathologica June 2016, Volume 131, Issue 6, pp 803–820 The 2016 World Health Organization Classification of Tumors of the Central Nervous System: a summary

Points for radiologists

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• Primitive neuroectodermal tumours  term has been removed and now the term used  is embryonal tumors with multilayered rosettes (ETMR).
• Two diffuse astrocytoma variants have been deleted from the WHO classification: protoplasmic astrocytoma, a diagnosis that was previously defined in only vague terms and is almost never made any longer given that tumors with this histological appearance are typically characterized as other more narrowly defined lesions; and fibrillary astrocytoma, since this diagnosis overlaps nearly entirely with the standard diffuse astrocytoma. 
• Gliomatosis cerebri was previously considered a distinct entity now merely thought of as a growth pattern.
• Glioblastoma with primitive neuronal component was added as a pattern in glioblastoma. This pattern, previously referred to in the literature as glioblastoma with PNET-like component, is usually comprised of a diffuse astrocytoma of any grade (or oligodendroglioma in rare cases) that has well-demarcated nodules containing primitive cells that display neuronal differentiation 
• Epithelioid glioblastoma is a variant of glioblastoma  only recently added to the WHO classification of CNS tumours as part of the 2016 update
• Diffuse midline glioma is a specific entity added only recently represents the majority of diffuse intrinsic pontine gliomas.
• Anaplastic pleomorphic xanthoastrocytoma, WHO grade III, has been added to the 2016 CNS WHO as a distinct entity, as opposed to the descriptive title of pleomorphic xanthoastrocytoma with anaplastic features in the past. 
• Although medulloblastoma has been classically thought of as a single entity in the 2016 update of the WHO classification of CNS tumours it is divided into four molecular subgroups: WNT, SHH, Group 3 and Group 4
• The WHO grade II diffuse astrocytomas and WHO grade III anaplastic astrocytomas are now each divided into IDH-mutant, IDH-wildtype and NOS categories. 
• New added  entity diffuse leptomeningeal glioneuronal tumor 
• The classification and grading of meningiomas did not undergo revisions, save for the introduction of brain invasion as a criterion for the diagnosis of atypical meningioma, WHO grade II.