Criteria

Pathological diagnosis

The World Health Organization (WHO) has produced guidelines for grading.[2][3]​​​ There are 3 grades of meningioma: 1, 2, and 3. The vast majority of tumours are classified as WHO grade 1 (benign). WHO grade 2 tumours are referred to as atypical, while WHO grade 3 tumours are malignant meningiomas. See Classification.​

The diagnostic criteria for WHO grade 2 and 3 tumours continues to evolve. In the 2007 update, there were changes with mitotic counts, which resulted in an increased prevalence of atypical meningiomas (from around 5% of cases, to 20% to 35% of all meningiomas).[4][59]​​​​ In the 2016 update, brain invasion was added as a criteria for WHO grade 2 meningioma.[60]​ The 2021 update added molecular criteria for WHO grade 3 meningioma (homozygous CDKN2A/B loss or TERT promoter mutation). It also replaced the use of roman numerals (I, II, III) with arabic numerals (1, 2, 3).[3]

The cIMPACT-NOW group has published a consensus on progress incorporating additional molecular criteria into the pathological diagnosis, and highlighted situations in which additional molecular testing may be considered.[61]​ In particular, situations to consider molecular testing include tumours with borderline histological criteria between WHO grade 1 and 2, brain-invasive but otherwise benign meningioma, tumours with rapid preoperative growth, and WHO grade 2 tumours.

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