WHO grading system for diffuse astrocytomas
The WHO grading system is the most widely used system for grading diffuse astrocytomas (at the time of writing i.e. mid-2016) and is an adaptation of the now superseded St Anne-Mayo grading system (also known as the Daumas-Duport grading system).
Grade I 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 II: low grade infiltrative astrocytoma
- cellular atypia only
- Grade III: anaplastic astrocytoma
- increased mitotic activity
- cellular anaplasia
- Grade IV: glioblastoma
- 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 . 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.