What is the grading of meningioma (brain tumor)?

From the Guidelines

Meningiomas should be graded according to the World Health Organization (WHO) classification system, which categorizes them into three grades based on histopathological features, with the most recent update incorporating molecular biomarkers such as oncogenic variants in the TERT promoter and homozygous deletion of CDKN2A/B as independent diagnostic criteria for CNS WHO grade 3, as recommended by the cIMPACT-NOW update 8 1. The grading of meningiomas is crucial for determining prognosis and treatment approach. The WHO classification system grades meningiomas into three grades:

• Grade I meningiomas are benign tumors with low recurrence rates, accounting for about 80% of all meningiomas, and show typical histological patterns such as meningothelial, fibrous, or transitional subtypes without aggressive features.
• Grade II (atypical) meningiomas represent 15-20% of cases and demonstrate increased mitotic activity (4-19 mitoses per 10 high-power fields), brain invasion, or at least three of the following features: increased cellularity, small cell formation, prominent nucleoli, sheet-like growth, or spontaneous necrosis.
• Grade III (anaplastic/malignant) meningiomas are rare (1-3%) and exhibit malignant features including 20 or more mitoses per 10 high-power fields or frank anaplastic/sarcomatous histology. The cIMPACT-NOW update 8 provides guidance for more standardized morphological evaluation and interpretation, and recommends assigning CNS WHO grade 2 for cases with CNS WHO grade 1 morphology but chromosomal arm 1p deletion in combination with 22q deletion and/or NF2 oncogenic variants 1. Some key points to consider when grading meningiomas include:
• Brain-invasive but otherwise morphologically benign (BIOB) meningiomas should not be graded before molecular data are obtained that further inform grading 1.
• Cases with borderline morphological grading criteria should undergo additional molecular testing 1.
• Histologically low-grade or borderline meningiomas with chromosome 1p deletion and concurrent 22q deletion/NF2 oncogenic variant should be assigned to “CNS WHO grade 2,” unless further molecular markers indicating CNS WHO grade 3 are present 1. The most recent study on the topic, published in 2025, provides the most up-to-date guidance on the grading of meningiomas, and should be used as the primary reference for clinical decision-making 1.

From the Research

Grading of Meningioma

The World Health Organization (WHO) grading system for meningiomas is based on histologic criteria, and includes:

• Grade 1 meningiomas, which are benign
• Grade 2 meningiomas, which exhibit intermediately aggressive behavior and usually manifest histologic atypia
• Grade 3 meningiomas, which demonstrate aggressive malignant behavior 2

Characteristics of Each Grade

• Grade 1 meningiomas are typically suitable for observation with serial imaging, but may require aggressive management with surgery and adjuvant radiotherapy in some cases 2, 3
• Grade 2 meningiomas account for approximately 20% of all meningiomas, and treatment options include surgical resection with or without adjuvant radiation therapy, definitive radiation therapy, and observation 4
• Grade 3 meningiomas are rare and aggressive, with high rates of recurrence, and treatment options include surgical resection and adjuvant radiotherapy 5

Molecular Classification and Grading

• The current WHO grading scheme is based predominantly on histologic features, but does not consistently reflect the biologic behavior of meningiomas 6
• Molecular features, such as genomic landscape and molecular characteristics, can provide greater understanding of meningiomas and improve diagnosis and classification 6
• Future classification schemes may benefit from an integrated approach that combines histopathology with genomic and epigenomic factors 6