Optic Nerve Sheath Meningioma

Optic nerve sheath meningioma (ONSM) is a rare, benign tumor that arises from the meninges (coverings) surrounding the optic nerve. Although not cancerous, it progressively compresses the optic nerve and its blood supply, causing gradual vision loss.

Understanding Optic Nerve Sheath Meningioma

ONSM grows from the arachnoid cells that form part of the optic nerve's protective covering. As the tumor grows, it encircles the optic nerve, squeezing it and compromising its blood supply. The tumor grows very slowly but progressively impairs vision.

Symptoms

Visual Symptoms

• Gradual vision loss—develops over months to years
• Color vision changes—colors appear faded
• Visual field deficits
• Dimming of vision with eye movement (gaze-evoked amaurosis)
• Usually affects one eye

Other Symptoms

• Eye pain (sometimes)
• Mild proptosis (eye bulging forward)
• Double vision (occasionally)

Classic Triad (Not Always Present)

1. Progressive vision loss
2. Optic atrophy (pale optic disc)
3. Optociliary shunt vessels (abnormal blood vessels on disc)

Who Gets ONSM?

• Middle-aged adults—peak age 40-50
• Women more often than men (3:1)
• May occur in children (more aggressive)
• Associated with neurofibromatosis type 2 (NF2) in some cases

Diagnosis

Clinical Examination

• Visual acuity—often reduced
• Color vision testing—affected early
• Visual field testing—various patterns
• Pupil examination—relative afferent pupillary defect
• Fundus examination—optic disc changes

Imaging

MRI orbits and brain with contrast

• Best diagnostic test
• Shows "tram-track" sign (tumor surrounding nerve)
• Enhancement with contrast
• Can distinguish from other lesions

CT scan

• May show calcification
• Useful for surgical planning

Treatment

Treatment decisions balance vision preservation against treatment risks:

Observation

For:

• Mild or stable vision loss
• Older patients
• Good vision in affected eye
• Patient preference

Involves:

• Regular monitoring (MRI, visual fields, acuity)
• Intervene if progression

Fractionated Radiation Therapy

Standard treatment when intervention needed

• Multiple small doses over several weeks
• Can stabilize or improve vision
• Generally well-tolerated
• Long-term success in most patients

Stereotactic Radiosurgery

• Single high-dose focused radiation
• Alternative to fractionated treatment
• Good results in selected cases

Surgery

Generally avoided because:

• Difficult to remove without damaging nerve
• High risk of vision loss
• Reserved for blind eyes (for cosmesis or comfort)
• Or specific situations (biopsy, decompression)

Prognosis

Natural History (Untreated)

• Slow but progressive vision loss
• Most patients eventually become blind in affected eye
• Very slow timeline—often years to decades

With Treatment

• Radiation can stabilize or improve vision
• Better outcomes with earlier treatment
• Some patients maintain useful vision long-term

Life Expectancy

• Normal—tumor is benign
• Does not spread to rest of body
• Monitoring is lifelong

Frequently Asked Questions

Is this cancer?

No. ONSM is a benign tumor—it doesn't spread to other parts of the body. However, because it grows around the optic nerve, it can cause significant vision loss if not managed appropriately.

Why not just remove the tumor surgically?

The tumor wraps around the optic nerve and its blood supply. Removing it usually requires sacrificing the nerve, resulting in blindness. Surgery is typically only offered when the eye is already blind.

Will radiation work?

Radiation is effective at stabilizing vision in many patients and can even improve vision in some. It's generally well-tolerated, though there are some risks. Your doctor will discuss whether radiation is appropriate for your situation.

How fast will I lose vision?

ONSM grows very slowly—often over years or even decades. Some patients maintain useful vision for many years. Regular monitoring helps determine if and when treatment is needed.

Can it spread to my other eye?

Primary ONSM affecting one eye rarely spreads to the other. However, patients with neurofibromatosis type 2 may develop tumors in both eyes. The other eye should be monitored.

References