Fact-sheet: Optic nerve sheath meningioma
Updated on 03/20/2023 at 9:59 AM
Note : 0/10
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Definition
Benign tumor arising from arachnoid meningo-epithelial cells, either extending from an intracranial meningioma or developing in situ (20% of cases), with concentric (sheath-like) or eccentric growth.
Accounts for one-third of optic nerve tumors, 1 to 2% of meningiomas, and 2 to 3.5% of orbital tumors.
Clinical features
Decreased visual acuity
CT
Contrast-enhanced orbital CT:
- Spontaneously hyperdense enlargement of the optic nerve sheath (tram-track sign)
- Occasionally, calcifications
- Intense peripheral enhancement of the optic nerve
- Assess extension to the optic canal (canal enlargement...): important preoperatively as it affects the surgical approach
MRI
Orbital MRI:
- On T1: space-occupying orbital process, iso- or hypointense relative to the muscles, encasing the optic nerve
- On T2: hypointense or hyperintense depending on histologic subtype
- On post-gadolinium T1: intense enhancement surrounding the axonal bundle, which remains hypointense within the meningiomatous "sheath"
- On T2*: may help characterize intra- or peritumoral calcifications (psammomatous form)
Differential diagnosis
Optic pathway glioma: Unlike meningioma, optic pathway glioma results in loss of visualization of the optic nerve margins.
