Optic nerve sheath meningioma

Overview


Optic nerve sheath meningiomas (ONSM) are rare benign tumors of the optic nerve. 60-70% of cases occur in middle age females, and is more common in older adults (mean age 44.7 years). It is also seen in children, but this is rare. The tumors grow from cells that surround the optic nerve, and as the tumor grows, it compresses the optic nerve. This causes loss of vision in the affected eye. 

It is typically a slow growing tumor, and has never been reported to cause death. However, there is concern that the tumor can grow into the brain and cause other types of neurological damage. In some patients, the tumor grows so slowly that treatment is not necessary. Standard treatments are observation, surgery, radiation therapy, and combinations of the above. 

Incidence
About 1-2% of all meningiomas are optic nerve sheath meningiomas. Meningiomas have an incidence of ~4.18/100,000 persons each year. Thus, ~10,000 meningiomas are diagnosed in the US each year; corresponding to ~100 cases of ONSM each year in the US. The actual number of meningiomas is likely much higher as it is very common in elederly women. ONSM comprises about 2% of orbital tumors, and about 10% of optic nerve lesions.

Neurofibromatosis type II (NF-2) affects around 9% of ONSM patients, where the incidence in the general population is around 0.03-0.05%. Thus NF-2 is felt to be a risk factor for the development of ONSM.

Diagnosis
Usually diagnosis can be achieved by an MRI of the brain or orbits when the patient presents with chronic visual loss, optic disc atrophy, and retinocilliary shunt vessels (the so called Hoyt-Spencer triad).

Treatment
Most ophthalmologists will not advocate any treatment unless visual loss is present and ongoing. Reports of patients with ONSM having no change in their vision for multiple years are not uncommon. If loss of vision occurs, radiation therapy will improve vision in about 1/3rd of cases, and preserve vision in about 1/3rd of cases. Surgery has traditionally been associated with rapid deteroriation of vision. However, newer surgical techniques may prove better for the treatment of ONSM.