By Prem Subramanian, M.D., Ph.D. (University of Colorado)

What is optic nerve sheath meningioma? And how common is it?

It is a benign, slow growing, tumor that arises from the sheath that surrounds the optic nerve. It accounts for 2% of orbital neoplasms and 2% of all meningiomas. It is the second most common optic nerve tumor accounting for one third of optic nerve neoplasms (most common is optic nerve glioma). Unlike gliomas, however, optic nerve meningioma tends to affect adults more than children, with a mean age of presentation of 40. However, if children are affected the tumor tends to be more aggressive in terms of growth, size, propensity to become cancerous, and recurrence rate. In general, they are unilateral and more common in females.

What are the symptoms of optic nerve sheath meningioma?

The most common presenting symptom is progressive loss of vision or visual field. Other symptoms include blind spots (scotomas), decrease in color vision, transient vision loss in different gazes. Eye bulging, lid edema, and limitation of eye movements can also occur. Less common and non-specific complaints include orbital pain and headaches, which have been reported in 2–50% of patients with ONSM.

Why should you seek a specialist?

Optic nerve sheath meningioma (ONSM) can progress if left unattended and lead to severe, even complete, vision loss. It may also spread toward the brain or to the optic nerve on the unaffected side. Rarely, malignant transformation or spread into the brain can occur.

How to diagnose optic nerve sheath meningioma?

Eye exam will often show a swollen or pale optic nerve. Enlarged vessels called optociliary shunt vessels may appear, indicating that the tumor is compressing the veins draining blood from the eye. Magnetic resonance imaging is the gold standard for visualization of ONSM. Advances in neuroimaging have allowed the diagnosis of ONSM to be made on the basis of clinical and neuroimaging findings without the need for biopsy. Early detection is the key to initiate intervention and prevent growth.

What are treatment options?

Because the main effect of ONSM is vision loss, the goal of treatment is to preserve vision. Hence, treatment is recommended in cases of progressive vision loss. Observation can be warranted if the tumor is small and not affecting vision, but the patient should be monitored closely with regular follow-ups.

Current preferred treatment modality is radiation therapy, with reported preservation of vision in more than 80% of cases. Surgical resection almost always causes vision loss and is reserved for blind, painful eyes or in cases of progressive changes concerning for cancer.