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Findings

Enlargement of the intraorbital portion of the left optic nerve

Isointense signal on T1WI

Enhancement around periphery of enlarged optic nerve

No edema within the optic nerve

No enhancement of the optic nerve itself

Differential diagnosis

Optic nerve sheath meningioma

Optic neuritis

Orbital pseudotumor

Sarcoidosis

Optic nerve glioma

Lymphoma

Metastases

Optic Nerve Sheath Meningioma

Benign, slow-growing neoplasm of intraorbital optic nerve dural sheath

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

90% of meningiomas that involve the obit are secondary lesions

Imaging finding

Enhancing mass surrounding optic nerve with calcification

Solid, tubular, enhancing, well-defined enlargement of the optic nerve

“tram-tracking” appearance

Linear or punctate calcification is characteristic

“Perioptic cysts” are a specific feature

Clinical

Slow, painless, progressive unilateral vision loss and proptosis

Other signs include diplopia and sudden vision obscuration

Fundoscopic exam

Optic nerve swelling and pallor

Optocilliary venous shunting in association with optic disc changes is very suggestive of ONSM

Typically presents in 4th and 5th decades

In juvenile patients more likely to be associated with NF2, and are more aggressive

More common in females (2-4:1)

Natural history

Progressive but slow vision loss is expected in most untreated patients

More aggressive in juvenile patients

Post-operative visual impairment common because tumor is tightly adherent to pia and shares blood supply

Treatment

Stereotactic radiotherapy currently considered 1st line therapy for patients with preservable vision but progressive impairment

Observation is recommended if vision is good and stable

Surgical excision indicated for tumor control if there is intracranial extension or if vision preservation is not possible