WHO grading system for diffuse astrocytomas

Last revised by Henry Knipe on 1 May 2023

The WHO grading system is the most widely used system for grading diffuse astrocytomas (c.2022) and is an adaptation of the now superseded St Anne-Mayo grading system (also known as the Daumas-Duport grading system). 

Grade 1 is reserved for localized astrocytomas (see WHO classification of CNS tumors for a complete list) and as such diffuse astrocytomas range in grade from grade II to IV:

  • grade 2: low-grade infiltrative astrocytoma

    • cellular atypia only

  • grade 3: previously known as anaplastic astrocytoma

    • increased mitotic activity

    • cellular anaplasia

  • grade 4: previously equivalent to glioblastoma, now depends on molecular characteristics

    • vascular proliferation

    • necrosis typically with perinecrotic palisading

Gliomatosis cerebri does not have its own grade but rather is a highly infiltrative version of a low grade or anaplastic tumor which involves at least three lobes 5. It does, however, confer a worse prognosis. 

It is worth noting that there are other grading systems (see diffuse astrocytoma grading) and the pros and cons of each have been the subject of extensive debate. 

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