WHO grading system for diffuse astrocytomas

Last revised by Assoc Prof Frank Gaillard on 08 Feb 2022

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used system for grading diffuse astrocytomas (at the time of writing i.e. early 2022) and is an adaptation of the now superseded St Anne-Mayo grading system (also known as the Daumas-Duport grading system).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