Meningioma Grading
WHO 2021 CNS Classification
Diagnostic Tiers
WHO Grade I (Benign)
• Mitotic index < 4 per 10 HPF.
• Lack of brain invasion or malignant molecular features.
• Includes Psammomatous, Meningothelial subtypes.
WHO Grade II (Atypical)
• Mitotic index 4-19 per 10 HPF.
• Brain invasion (macro/microscopic).
• Clear cell or Chordoid histotypes.
WHO Grade III (Anaplastic)
• Mitotic index ≥ 20 per 10 HPF.
• Papillary or Rhabdoid histotypes.
• TERT promoter mutation (Automatic Grade 3).
Molecular Upgrade Rules
Histologic appearances can be deceiving. Genetic markers now override morphology in the latest WHO standards.
TERT Promoter
Presence of TERT mutation upgrades a CNS WHO grade 1 or 2 meningioma to Grade 3.
CDKN2A/B Deletion
Homozygous deletion of CDKN2A and/or CDKN2B upgrades to Grade 3.
Surgical Margin
Correlation with Simpson Grade (Extent of Resection) is vital for recurrence prediction.
Verified
Last Review: 2026
Last Comprehensive Review: 2026