The 2021 World Health Organization Classification of Tumors of the Central Nervous System: What Neuroradiologists Need to Know

Abstract

Neuroradiologists play a key role in brain tumor diagnosis and management. Staying current with the latest classification systems and diagnostic markers is important to provide optimal patient care. Publication of the 2016 World Health Organization Classification of Tumors of the Central Nervous System introduced a paradigm shift in the diagnosis of CNS neoplasms. For the first time, both histologic features and genetic alterations were incorporated into the diagnostic framework, classifying and grading brain tumors. The newly published 2021 World Health Organization Classification of Tumors of the Central Nervous System, May 2021, 5th edition, has added even more molecular features and updated pathologic diagnoses. We present, summarize, and illustrate the most salient aspects of the new 5th edition. We have selected the key "must know" topics for practicing neuroradiologists.ABBREVIATIONS: DGONC ¼ diffuse glioneuronal tumor with oligodendroglioma-like features and nuclear clusters; EPN ¼ ependymoma; ETMR ¼ embryonal tumor with multilayered rosettes; FISH ¼ fluorescence in situ hybridization; NEC ¼ not elsewhere classified; NOS = not otherwise specified; MB ¼ medulloblastoma; MGNT ¼ myxoid glioneuronal tumor; MVNT ¼ multinodular and vacuolating neuronal tumor; PF ¼ posterior fossa; SC ¼ spinal cord; ST ¼ supratentorial; WHO ¼ World Health Organization; IDH ¼ isocitrate dehydrogenase

Study of histopathology of tumors of the central nervous system in a teaching hospital

“…In our study, the most common symptom encountered was headache (62 %), followed by convulsions (30 %), vomiting (29 %) and visual disturbances (27 %). The predominance of headaches in intracranial tumours follows other studies by Nelson S et al [4].…”

“…In the present study, gliomas are the most common tumours, among which astrocytomas were predominant (59.4 %), followed by glioblastomas (35.1 %) and oligodendrogliomas (5.4 %). The grading system adopted is according to the WHO system [4]. Most astrocytomas are seen in males compared to females, and the highest frequency has been noted in the 4 th and 5 th decades of life.…”

“…The current state of neuroimaging has evolved into a comprehensive diagnostic tool for characterising morphologic and biologic alterations to diagnose and grade brain tumours and assess treatment response and prognosis. MRI has become the primary imaging modality for brain tumours and is primely used in the pre and post-operative evaluation of patients [4]. However, this has limitations; the findings are not specific to a tumour or lesion.…”

The complex interactions between the cellular and non-cellular components of the brain tumor microenvironmental landscape and their therapeutic implications

“…IDH-mutant diffuse astrocytomas are now classified 2-4 grade; the designations “anaplastic astrocytoma” and “glioblastoma” have been dropped for IDH-mutant astrocytomas. Furthermore, if an IDH-mutant diffuse astrocytoma has a homozygous deletion of CDKN2A/B, it is classified as a CNS WHO grade 4 neoplasm, even though histologic signs of malignancy such as necrosis and microvascular proliferation are lacking ( 39 , 45 , 46 ). Roman numerals are no longer used to denote WHO grades; instead, Arabic numbers are used.…”

“…For example, noncanonical (such as non-R132H) IDH1 and IDH2 mutations should be examined in patients 55 years of age and younger with IDH-wildtype diffuse astrocytic gliomas. Other molecular markers, such as ATRX expression loss or TERT promoter mutations, presence of TP53 or histone H3 mutations, EGFR amplification, or CDKN2A/B changes, must be investigated ( 39 , 45 , 46 ).…”