CNS tumor

Diffuse astrocytic and oligodendroglial tumors

WHO grading-astrocytomas

Topic Completed: 1 August 2017

Minor changes: 6 July 2021

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PubMed Search: WHO grading of astrocytomas [title]

Eman Abdelzaher, M.D., Ph.D.
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Cite this page: Abdelzaher E. WHO grading-astrocytomas. website. Accessed October 25th, 2021.
Histological grading of diffuse astrocytic tumors
  • According to the 2016 WHO classification, diffuse astrocytomas are graded using a three tiered system (II, III and IV); there are no grade I infiltrating astrocytomas
  • WHO grading scheme is based on the presence or absence of four histological parameters:

    1. Nuclear atypia: defined as nuclear pleomorphism and hyperchromasia

    2. Mitoses
    • Must be unequivocal
    • Solitary mitosis in a large specimen does not justify the WHO grade III designation
    • Ki67 proliferation index aids in the separation of grade II from grade III tumors

    3. Microvascular proliferation: two forms are recognized
    • Glomeruloid type, which is more common but prognostically less significant since it is also commonly encountered in low grade gliomas such as pilocytic astrocytoma
    • Endothelial proliferation within the lumen of larger vessels, which is less common but is more closely associated with high grade gliomas

    4. Necrosis: two types are recognized
    • Coagulative necrosis
    • Pseudopalisading necrosis
WHO histological grading of diffuse astrocytic tumors
  • WHO grade II tumors (diffuse astrocytoma): show only nuclear atypia
  • WHO grade III tumors (anaplastic astrocytoma): show nuclear atypia with focal or dispersed anaplasia, significant proliferative activity and mitoses
  • WHO grade IV tumors (glioblastoma): show nuclear atypia, mitoses, microvascular proliferation or necrosis
WHO histological grading of localized astrocytic tumors
  • Pilocytic astrocytoma corresponds to WHO grade I
    • For now, a definite grade assignment is not recommended for pilomyxoid astrocytoma
  • Subependymal giant cell astrocytoma corresponds to WHO grade I
  • Pleomorphic xanthoastrocytoma corresponds to WHO grade II and anaplastic pleomorphic xanthoastrocytoma corresponds to WHO grade III
Additional references
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