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Optic nerve sheath meningioma (ONSM) is a benign, slow-growing tumor that arises from the arachnoid cap cells of the optic nerve sheath. It typically surrounds the optic nerve without invading its fibers, leading to progressive visual loss through compression and ischemia.

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Epidemiology

Accounts for 1–2% of all meningiomas
Second most common optic nerve tumor (after optic pathway glioma)
Peak incidence: 40–60 years
Strong female predominance (~3:1)
Bilateral involvement is rare but can occur in Neurofibromatosis type 2 (NF2)

Clinical Features

Painless, progressive unilateral visual loss
Optic disc pallor (optic atrophy) or optic disc swelling
Proptosis (mild to moderate)
Optociliary shunt vessels (retinal venous collaterals)
Color vision loss and visual field defects (commonly central or cecocentral scotomas)

Radiology:

Imaging features:

Feature	Description
T1-weighted MRI	Isointense to optic nerve
T2-weighted MRI	Variable; often iso- to hypointense
Post-contrast	Intense, homogeneous enhancement of tumor encasing the optic nerve
Tram-track sign (classic)	Enhancing sheath with non-enhancing central optic nerve on axial images
En-plaque pattern	Long segment circumferential thickening of optic nerve sheath
Calcifications (on CT)	Common, appear as tram-track calcifications
Bone remodeling	Hyperostosis of adjacent orbital walls may be seen

![Optic nerve sheath meningioma. Axial (A) and coronal (B) gadolinium-enhanced, fat-suppressed, T1-weighted images obtained in a 77-year-old female with progressive right vision loss demonstrate abnormal thickening and enhancement of the right optic nerve sheath compatible with optic nerve sheath meningioma. The nerve sheath thickening and enhancement produce a “tram-track” configuration (arrows, A) in the axial image and a “donut” configuration (arrow, B) in the coronal image. Axial CT image (C) obtained in a 45-year-old female with neurofibromatosis type 2 demonstrates the “tram-track” calcifications (arrow, C) present in 20% to 50% of these tumors.

Bunch PM, Sachs JR, Kelly HR, Lipford ME, West TG. Magnetic Resonance Imaging of Head and Neck Emergencies, a Symptom-Based Review, Part 1. Magnetic Resonance Imaging Clinics of North America. 2022;30(3):409-424. doi:https://doi.org/10.1016/j.mric.2022.04.005](attachment:d85d7f59-5361-4641-a317-411d8d5b2cad:1-s2.0-S1064968922000253-gr6_lrg.jpg)

Optic nerve sheath meningioma. Axial (A) and coronal (B) gadolinium-enhanced, fat-suppressed, T1-weighted images obtained in a 77-year-old female with progressive right vision loss demonstrate abnormal thickening and enhancement of the right optic nerve sheath compatible with optic nerve sheath meningioma. The nerve sheath thickening and enhancement produce a “tram-track” configuration (arrows, A) in the axial image and a “donut” configuration (arrow, B) in the coronal image. Axial CT image (C) obtained in a 45-year-old female with neurofibromatosis type 2 demonstrates the “tram-track” calcifications (arrow, C) present in 20% to 50% of these tumors.