CNS tumor
Diffuse astrocytic and oligodendroglial tumors
WHO grading-astrocytomas
Author: Eman Abdelzaher, M.D., Ph.D.
Topic Completed: 1 August 2017
Minor changes: 26 August 2020
Copyright: 2002-2021, PathologyOutlines.com, Inc.
PubMed Search: WHO grading of astrocytomas [title]
Table of Contents
Histological grading of diffuse astrocytic tumors | WHO histological grading of diffuse astrocytic tumors | WHO histological grading of localized astrocytic tumors | Additional referencesCite this page: Abdelzaher E. WHO grading-astrocytomas. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/cnstumorwhograding.html. Accessed January 17th, 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
