Optic nerve sheath meningioma (ONSM) is a nonaggressive and slow-growing tumor in the eye. They usually grow over the layer that covers the optic nerve in the eye. Meningiomas are the most common tumors diagnosed inside the skull. Due to their slow-growing nature, they are not fatal, but they may interfere with vision. Optic nerve sheath meningioma has been reported in all age groups but is most common in women in their thirties. The patient may not have any signs and symptoms for many years. The most seen signs and symptoms of ONSM are:
- Loss of vision: Optic nerve compression can cause loss of vision. Depending on the location, size, and degree of optic nerve involvement, patients may develop visual disturbances, such as blurred vision, darker vision, dimmed vision, or progressive loss of vision of the affected eye.
- Bulging eye or proptosis: Optic nerve meningioma can extend from the brain into the orbit (behind the eye) and push the eye forward causing a bulging of the eye. Due to the bulge, patients may have limitations in eye movements, which often cause problems like double vision.
What is the optic nerve?
The optic nerve is a bundle of nerve fibers that are part of the central nervous system. They are located at the back of the eye and serve as communication cables between the eyes and brain. They use electrical impulses to transfer visual information from the retina to the vision centers of the brain. When the optic nerve is squeezed due to tumors or cancers, the blood supply and ability to send the messages and signals through the nerve may be impaired.
What are the causes of ONSM?
The cause of optic nerve sheath meningioma is still unknown, and research is still being conducted.
- Exposure to ionizing radiation: Ionizing radiation may cause two types of harm to humans: direct tissue damage and cancer, which also include ONSM.
- Neurofibromatosis type 2: It is a condition in which the nervous system develops noncancerous tumors. It is mostly hereditary.
- Chromosome abnormality: A few people with ONSM has improper chromosome 22 abnormality, including the region containing the NF2 gene.
How is optic nerve sheath meningioma diagnosed?
Vision examination, magnetic resonance imaging (MRI), ultrasonography, and computed tomography (CT) imaging of the head is usually considered for diagnosing optic nerve sheath meningioma. The findings include:
- Vision loss: Vision is measured by testing on a vision chart. This is usually reduced or may be mildly affected. The doctor may notice that there is less amount of light going into the affected eye by swinging a bright light from one eye to the other.
- Change in optic nerve vessels: The back of the eye often shows changes including swelling of the beginning of the nerve or relative thinning of the optic nerve due to calcification. Enlarged blood vessels also called optociliary shunt vessels are usually seen in imaging.
- The eye may have been pushed forward by the optic nerve sheath meningioma.
How is optic nerve sheath meningioma treated?
Treatment may not be required if the tumor is slow-growing and not causing symptoms. In younger patients, however, the tumor is more likely to be aggressive and fast-growing, which may be an indication for surgery. Treatment plans include:
- Wait and watch: Orbital meningioma is typically a slow-growing tumor. Once diagnosed, meningioma can be observed for growth prior to considering intervention. Observation is the acceptable management in cases where the visual function is intact or remains stable, especially in patients who maintain a better vision.
- Radiotherapy: Radiotherapy has been used both pre-operatively and postoperatively for many years. Stereotactic radiotherapy delivers the appropriate amount of radiation to the tumor in a localized fashion. However, damage to the optic nerve and retina are the side effects.
- Endoscopic procedure: Transnasal endoscopic optic nerve decompression has shown stabilization of the disease and in some cases, improvement in the vision.
- Tumor resection: In rare cases, the tumor is surgically removed, especially if the tumor is spreading and an individual lost most of the vision. Tumor resection is also considered in conditions when the patient has a bulging eye. Unfortunately, surgery may damage the nerve and cause vision to get worse. Sometimes, radiotherapy is given after surgery to reduce the risk of it coming back later in life. Unfortunately, radiotherapy may also damage the vision.