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Optic Nerve Sheath Meningioma


KEY FACTS

Terminology

  • Optic nerve sheath meningioma

    • Also known as perioptic meningioma

  • Benign, slow-growing tumor of optic nerve sheath

  • Distinct entity from intracranial (spheno-orbital) meningioma that extends through orbital apex into orbit

Imaging

  • NECT

    • “Tram-track” Ca++ on either side of optic nerve

      • –

        Seen in 1/3 to 1/2 of cases

  • CECT

    • Tubular enhancing mass surrounding intraorbital optic nerve

  • MR

    • Variably hyperintense to hypointense on T2WI

    • Uniform, moderately intense enhancement

Top Differential Diagnoses

  • Optic nerve glioma

  • Orbital pseudotumor

  • Orbital sarcoidosis

  • Metastasis

  • Orbit lymphoproliferative lesions

Pathology

  • Benign tumor arising from arachnoid “cap” cells within optic nerve sheath

  • May be associated with neurofibromatosis type 2

Clinical Issues

  • Classic: Visual loss, optic atrophy, optociliary venous shunting, choroidal fold

  • Fractionated radiosurgery currently first-line therapy

Diagnostic Checklist

  • MR is preferred imaging modality for tumor assessment, but look for Ca++ on CT when diagnosis in doubt

Axial graphic depicts a fusiform meningioma
arising from the optic nerve sheath. Characteristic “perioptic cyst” evident behind the globe
represents trapped cerebrospinal fluid within the nerve sheath.

Funduscopic examination in a patient with optic nerve sheath meningioma shows optic disc edema and pallor
together with prominent choroidal folds
.

NECT scan shows typical “tram track” calcifications
of optic nerve sheath meningioma. No obvious soft tissue abnormality is seen on this noncontrast CT study.

Axial T1WI C+ FS MR in another case shows a symmetric en plaque thickening/enhancement of the left nerve sheath characteristic of meningioma
. Enhancing tumor outlining the nerve results in the “tram-tracks” mimicking calcification described on CT.

TERMINOLOGY

Abbreviations

  • Optic nerve sheath meningioma (ONSM)

Synonyms

  • Perioptic meningioma

Definitions

  • Benign, slow-growing neoplasm of optic nerve (ON) dural sheath

  • Distinct entity from intracranial (spheno-orbital) meningioma that extends through orbital apex

    • 90% of meningiomas that involve orbit are secondary lesions rather than primary ONSM

IMAGING

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