CNS tumor

Meningeal tumors

Atypical meningioma



Topic Completed: 29 March 2021

Minor changes: 29 March 2021

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PubMed Search: Atypical meningioma[TI] free full text[sb]

Chunyu Cai, M.D., Ph.D.
Anthony T. Yachnis, M.D.
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Cite this page: Cai C, Kresak J, Yachnis A. Atypical meningioma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/cnstumoratypicalmeningioma.html. Accessed November 27th, 2021.
Definition / general
  • A meningioma of intermediate aggressiveness between benign and malignant forms, comprising 5 - 15% of meningiomas
  • WHO grade II
  • Diagnostic criteria: fulfilling either 1 of 2 major criteria or 3 of 5 minor criteria
    • Major criteria:
      • 4 - 19 mitotic figures/10 high power fields
      • Brain invasion
    • Minor criteria:
      • Increased cellularity
      • Small cells with high N/C ratio
      • Large and prominent nucleoli
      • Patternless or sheet-like growth (loss of lobular architecture)
      • Foci of spontaneous or geographic necrosis
  • Invasion of dura, bone or soft tissue does not affect grading
  • Pleomorphic or atypical nuclei do not affect grade
  • Ki67 is not a true diagnostic criteria; however, it is usually greater than 4% and up to 20%
Essential features
  • Atypical meningiomas have an intermediate recurrence rate between benign and malignant meningiomas
  • 29 - 52% recur (versus 7 - 25% of classic meningiomas and 50 - 94% of anaplastic meningiomas) (Louis: WHO Classification of Tumours of the Central Nervous System, 4th Edition, 2016)
  • Molecular genetic and epigenetic signatures of atypical meningiomas are becoming increasingly important in predicting prognosis and new targeted therapy in progressive tumors
ICD coding
  • ICD-10: D32.9 - benign neoplasm of meninges, unspecified
Epidemiology
Sites
  • Intracranial, intraspinal or intraorbital
Pathophysiology
  • Arising from the meningothelial cells or the arachnoid layer
Etiology
Clinical features
  • Clinical presentation of atypical and anaplastic meningioma is similar to their benign counterpart
  • Common symptoms include headaches, seizures and focal neurological deficit due to tumor compression (Neurosurg Clin N Am 2016;27:239)
Diagnosis
  • Diagnose by imaging and pathology of biopsy / resection specimen
Radiology description
  • Extra-axial mass with dural tail
  • Uniformly contrast enhancing
  • Extensive peritumoral edema is associated with brain invasion (Neuro Oncol 2020 Aug 13 [Epub ahead of print])
  • Several benign meningioma variants, including angiomatous, microcystic, secretory and lymphoplasmacyterich meningiomas may also have prominent peritumoral edema (J Neurooncol 2013;111:49)
Prognostic factors
  • Extent of surgery and WHO grading
  • DNA methylation profiling may better predict tumor recurrence and prognosis than histologic classification (Lancet Oncol 2017;18:682)
Case reports
  • 36 and 70 year old women with optic nerve seeding of atypical meningiomas presenting with subacute visual loss (J Neurosurg 2013;119:494)
  • 44 year old man with atypical primary meningioma in the nasal septum with malignant transformation and distant metastasis (BMC Cancer 2012;12:275)
  • Elderly man with metastatic atypical meningioma (J Clin Neurosci 2000;7:69)
Treatment
  • Gross total resection
  • Postsurgical radiation is often offered for atypical meningiomas, especially after a subtotal resection (J Neurooncol 2013;115:241)
  • Stereotactic radiosurgery
Gross description
Frozen section description
Microscopic (histologic) description
  • May have histology of any grade I variant meningioma with increased mitoses (4 - 19/10 high power fields)
    • Mitotic rate is defined as the highest count over 10 consecutive high power fields (1 high power field = 0.16 mm²)
  • May have increased cellularity or areas of small cell collections
  • May have sheet-like growth pattern
  • May have areas of spontaneous necrosis
  • May have macronucleoli
  • Brain invasion is defined as irregular projections of tumor cells into adjacent CNS parenchyma without an intervening layer of leptomeninges at the tumor to brain interphase (Am J Surg Pathol 1997;21:1455)
Microscopic (histologic) images

Contributed by Chunyu "Hunter" Cai, M.D., Ph.D.
Small cell change - meningothelial

Small cell change - meningothelial

Small cell change - transitional

Small cell change - transitional

Spontaneous necrosis

Spontaneous necrosis

Macronuclei

Macronuclei

Sheeting

Sheeting

Brain invasion - nest

Brain invasion - nest


Brain invasion - protrusions

Brain invasion - protrusions

Cytology description
  • Squash prep shows similar histology as standard meningioma but may also show occasional mitoses or macronucleoli
Negative stains
Molecular / cytogenetics description
  • Majority of atypical meningiomas have loss of NF2 combined with either genome instability (large scale chromosomal alterations) or loss of SMARCB1 (Nat Commun 2018;9:16215)
  • Recurrent losses of chromosome 1p, 6q, 14q,18q and gain of 1q are indicators of poor prognosis (Acta Neuropathol 2017;133:431)
  • Non-NF2 meningiomas are enriched in mutations in TRAF2, KLF4, AKT1 and SMO, most of which are benign and preferentially locate in skull base (Science 2013;339:1077)
  • DNA methylation profiling of meningioma distinguished 6 methylation classes (MCs), benign (ben) 1 - 3, intermediate (int) A and B and malignant (mal)
    • DNA methylation based meningioma classification is reported to better predict tumor recurrence and prognosis than the WHO histological classification (Lancet Oncol 2017;18:682)
  • NF2 mutant atypical meningiomas display increased H3K27me signal and a hypermethylated phenotype due to increased polycomb repressive complex 2 (PCR2) / EZH2 activity (Nat Commun 2018;9:16215)
Sample pathology report
  • Brain, right frontal lobe mass, excision:
    • Atypical meningioma (see comment)
    • Comment: Section shows a meningioma with predominant meningothelial morphology and rare psammoma bodies. Multiple atypical features are present, including variably increased mitotic index up to 7 mitoses/10HPF (A7), multifocal microscopic necrosis, widespread small cell change, hypercellularity, and sheeted architecture. No macronucleoli or brain invasion is identified. Ki67 proliferation index is 12.7% per 1,000 nuclei count.
Differential diagnosis
Board review style question #1

The arrows in the above image show which of the following?

  1. Blood vessels
  2. Lymphoplasmacytic inflammation
  3. Pseudopalisading necrosis
  4. Small cell change
Board review style answer #1
D. Small cell change

The image shows an atypical meningioma with small cell change, characterized by reduced cytoplasm and increased N/C ratio in these regions. These regions may resemble lymphoplasmacytic inflammation on low power but on high power show nuclei that are similar to adjacent tumor cells.

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Reference: Atypical meningioma
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