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Meningioma, CPA-IAC


KEY FACTS

Terminology

  • Definition: Benign, unencapsulated neoplasm arising from meningothelial arachnoid cells of CPA-IAC dura

Imaging

  • 10% occur in posterior fossa

  • When in CPA, asymmetric to IAC porus acusticus

  • NECT

    • Variable; often hyperdense

      • –

        25% calcified; 2 types seen

        • □

          Homogeneous, sand-like (psammomatous)

        • □

          Focal “sunburst,” globular, or rim pattern

  • Bone CT: Hyperostotic or permeative-sclerotic bone changes possible (en plaque type)

  • T2WI MR: Pial blood vessels seen as surface flow voids between tumor and brain

    • High signal crescent from CSF (“CSF cleft”)

  • T1WI C+ MR: Enhancing dural-based mass with dural “tails” centered along posterior petrous wall

    • When IAC tail present, usually dural reaction, not tumor

Top Differential Diagnoses

  • Vestibular schwannoma

  • Epidermoid cyst, CPA-IAC

  • Dural metastases, CPA-IAC

  • Sarcoidosis, CPA-IAC

  • Idiopathic inflammatory pseudotumor

Clinical Issues

  • 2nd most common CPA tumor

  • Slow-growing tumor, displacing adjacent structures

  • Often found as incidental brain MR finding

  • < 10% symptomatic; usually do not cause sensorineural hearing loss

  • Treatment

    • Follow with imaging if smaller size and older patient

    • Surgical removal if medically safe

    • Adjunctive radiation therapy with incomplete surgery

At level of the internal auditory canal (IAC), a large cerebellopontine angle (CPA) meningioma causes mass effect on the brainstem and cerebellum. Notice the broad dural base creating the shape of a mushroom cap. Dural “tails”
are present in ~ 60% of cases, typically representing reactive rather than neoplastic change. CSF-vascular cleft is also visible
.

Axial NECT scan in a 72-year-old woman shows a typical CPA meningioma as a hyperdense “mushroom cap-shaped” mass
with its broad base toward the adjacent temporal bone.

Axial T1WI C+ FS MR through the IAC shows a meningioma overlying the porus acusticus. Note the dural “tail”
extending along the temporal bone posterior wall. A dot of enhancement in the IAC fundus
suggests that the low signal area in the IAC is a nonenhancing meningioma.

Axial T2WI FS MR in the same patient reveals a high-velocity flow void
representing a dural artery feeder penetrating the meningioma core. Low signal in the IAC
is an intracanalicular meningioma.

TERMINOLOGY

Synonyms

  • Posterior fossa meningioma

Definitions

  • Benign, unencapsulated neoplasm arising from meningothelial arachnoid cells of CPA-IAC dura

IMAGING

General Features

  • Best diagnostic clue

    • CPA dural-based enhancing mass with dural “tails”

  • Location

    • 10% occur in posterior fossa

    • When in CPA, asymmetric to IAC porus acusticus

  • Size

    • Broad range; usually 1-8 cm but may be larger

    • Generally significantly larger than vestibular schwannoma at presentation

  • Morphology

    • 3 distinct morphologies

      • –

        “Mushroom cap” (hemispherical) with broad base toward posterior petrous wall (75%)

      • –

        Plaque-like (en plaque), ± bone invasion with hyperostosis (20%)

      • –

        Ovoid mass mimics vestibular schwannoma (5%)

    • Larger lesions often herniate superiorly through incisura into medial middle cranial fossa

CT Findings

  • NECT

    • 25% isodense, 75% hyperdense

    • 25% calcified; 2 types seen

      • –

        Homogeneous, sand-like (psammomatous)

      • –

        Focal “sunburst,” globular, or rim pattern

  • CECT

    • > 90% have strong, uniform enhancement

  • Bone CT

    • Hyperostotic or permeative-sclerotic bone changes possible (en plaque type)

    • IAC widening is rare (seen with vestibular schwannoma)

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