WHO Grade 2 Meningioma

WHO Grade 2 meningiomas, also called atypical meningiomas, represent an intermediate grade between benign (Grade 1) and malignant (Grade 3) tumors. They exhibit increased proliferative activity, brain invasion, or atypical histological features, and have a higher risk of recurrence and progression compared to Grade 1.

A WHO Grade 2 meningioma is defined by one or more of the following:

• Brain invasion (since WHO 2016, retained in 2021)
• Mitotic index ≥4 mitoses per 10 high-power fields (HPF)
• At least 3 of the following 5 histological features:
  1. Increased cellularity
  2. Small cells with high nuclear-to-cytoplasmic ratio
  3. Prominent nucleoli
  4. Sheet-like growth pattern
  5. Foci of spontaneous necrosis

• Atypical meningioma (most common)
• Clear cell meningioma (molecularly defined)
• Chordoid meningioma

• Mitotic activity ≥4 per 10 HPF
• Increased nuclear atypia and hypercellularity
• Brain invasion (any degree)
• Possible necrosis or architectural distortion
• May be diagnosed purely on molecular subtype (e.g. clear cell, chordoid)

• Loss of chromosome 1p, 14q, or CDKN2A/B deletions associated with worse prognosis
• DNA methylation profiling may further stratify recurrence risk

• Aggressive behavior compared to Grade 1
• Higher recurrence rate, even after complete resection
• Often present in younger patients or in non-skull-base locations

• Maximal safe surgical resection is primary treatment
• Simpson grade I–III resection is preferred
• Postoperative radiotherapy is often recommended, especially if:
  1. Resection is subtotal (Simpson grade IV–V)
  2. Brain invasion is present
  3. Tumor is recurrent
• Adjuvant RT improves progression-free survival but may not always be necessary after gross total resection

• 5-year recurrence-free survival:
  1. ~50–70% after gross total resection
  2. Worse with subtotal resection or brain invasion
• Regular MRI follow-up is essential, typically every 6–12 months for the first 5 years

• WHO Classification of Tumours Editorial Board. *WHO Classification of Tumours of the Central Nervous System*. 5th ed. IARC, 2021.
• Goldbrunner R, et al. EANO guideline on meningiomas. *Lancet Oncol*. 2016.
• Sahm F, et al. DNA methylation-based classification and grading of meningiomas. *Acta Neuropathol*. 2017.