Optic nerve sheath meningiomas (ONSM) are tumors common in middle-aged females
Typical MRI signs of ONSM are Tram track appearance and doughnut sign.
ONSM appears as a hyperintense thickened mass surrounding the optic nerve on T2-weighted MRI, enhancing with gadolinium. The optic nerve itself is typically neither enhancing nor enlarged. On coronal MRI cuts, the enhancing lesion around the optic nerve has been referred to as a “doughnut” sign, whereas on axial MRI imaging, the ONSM appears as a “tram-track” sign. This is due to contrast enhancement of the meningeal sheath around the optic nerve which itself remains not-enhanced. Thereby enhanced tram tracks (meningeal enhancement) juxtaposed with a darker-appearing optic nerve

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Optic nerve glioma on CT reveals

enlargement of the optic nerve and the mass may either be fusiform or exophytic in appearance.
enlargement of the optic canal
the optic nerve may be elongated with kinking or buckling
Optic Nerve Sheath Meningiomas are uncommon, benign neoplasms originating from the meningothelial cells of the meninges surrounding the optic nerve.
neurofibroma is a type of peripheral nerve tumor that forms soft bumps on or under the skin

Ref: Kanski clinical ophthalmology, edition 9, page 792

Neuro-Ophthalmic Disorders