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Atypical and Malignant Meningioma


KEY FACTS

Terminology

  • Typical (benign) meningioma = WHO grade I

  • Atypical meningioma (AM) = WHO grade II

  • Malignant meningioma (MM) = WHO grade III

Imaging

  • CT triad of MM: Extracranial mass, osteolysis, intracranial tumor

  • MR

    • Dural-based locally invasive lesion with areas of necrosis, marked brain edema

    • Indistinct tumor margins (tumor invades, interdigitates with brain)

    • Prominent tumor pannus extending away from mass = “mushrooming”

    • Marked peritumoral edema

    • DWI, ADC correlate with hypercellular histopathology (high signal on DWI, low ADC)

Top Differential Diagnoses

  • Meningioma (typical)

  • Dural metastasis

  • Lymphoma

  • Sarcoma (osteosarcoma, Ewing, gliosarcoma, etc.)

Pathology

  • AM: High mitotic activity

  • MM: AM features + findings of frank malignancy

Clinical Issues

  • AM 29% recurrence (26% become MM)

  • MM 50% recurrence

Diagnostic Checklist

  • Difficult to predict meningioma tumor grade on imaging

  • Imaging findings of typical meningioma do not exclude atypical, malignant variants

Coronal graphic illustrates a malignant meningioma infiltrating the scalp, skull, and underlying brain. Extensive vasogenic edema (in gray) is present. Note osteolysis, invasion through dura/arachnoid, tumor “mushrooming”
, and interdigitation with the brain.

Sagittal T1WI C+ MR of malignant meningioma shows enhancing tumor involving the scalp, skull, and underlying brain. Note “mushrooming” of tumor through the dura
, prominent hypointense brain edema
.

Axial T2WI MR in a 71-year-old man shows well-demarcated dural-based mass along right greater sphenoid wing
. Mass is isointense with cortex & distinct cerebrospinal fluid-vascular cleft
with no evidence for focal brain invasion.

Axial T1 C+ FS MR scan shows intense, uniform enhancement
. At surgery there was no evidence for invasion of adjacent parenchymal. Pathology disclosed WHO grade II meningioma. This case illustrates the difficulty of predicting meningioma tumor grade on imaging.

TERMINOLOGY

Abbreviations

  • Atypical meningioma (AM), malignant meningioma (MM)

Definitions

  • Typical (benign) meningioma = WHO grade 1

    • Common meningioma (CM)

  • Atypical meningioma = WHO grade 2

    • Papillary, clear cell meningiomas (CCM)

  • Malignant meningioma = WHO grade 3

    • Anaplastic meningioma

IMAGING

General Features

  • Best diagnostic clue

    • Dural-based, locally invasive lesion with areas of necrosis, marked brain edema

  • Location

    • May occur anywhere in neuraxis (brain > > spine)

    • AM (clear cell variant)

      • –

        Frequent in CPA, along tentorium

    • MM

      • –

        Parasagittal (44%), cerebral convexities (16%) most common sites

      • –

        Both AM, MM far less frequent in spine, skull base

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