What is Optic Nerve Cysts?
Optic nerve cysts refer to a range of conditions that cause fluid-filled sacs to form on the optic nerve, the nerve that transmits visual information from the eye to the brain. These cysts can form due to variety of reasons. They can be idiopathic, meaning we don’t know what causes them. They could arise from certain growths in the protective layers of the brain and spinal cord. They could also be traumatic, meaning they’re caused by injury, or iatrogenic, meaning they result from medical treatment or procedures.
Additionally, this topic also covers rare conditions like cystic eye or microphthalmos with a cyst. These are conditions present from birth where an eye is either small or not fully formed and often involves the optic nerve. Each of these conditions and causes are different, but they all contribute to the formation of optic nerve cysts.
What Causes Optic Nerve Cysts?
Cysts, or fluid-filled sacs, in the eye can be caused by a range of different factors. They may happen for no clear reason, or they can be related to other conditions such as meningiomas (tumors that grow from the protective coverings of the brain and spinal cord), meningoceles (protrusions of the meninges, the membranes that envelop the central nervous system), arachnoid cysts (fluid-filled sacs that occur on the arachnoid membrane, a thin layer covering the brain), neuroepithelial cysts (uncommon sacs that primarily occur in the brain cavities or brain tissue), and post-traumatic or surgical cysts.
Specifically, a condition called optic nerve sheath meningocele can cause cysts. This condition is an enlargement of the optic nerve sheath, which is a fluid-filled space located around the optic nerve. The optic nerve is what connects the eye to the brain.
Arachnoid cysts are non-cancerous growths that develop on a membrane surrounding the optic nerve. These are mostly made from normal tissue. Neuroepithelial cysts are rare and mainly appear in the brain cavities or brain tissue, though they have occasionally been found in the optic nerve.
Medical procedures can also lead to cysts. For instance, Naqvi et al. documented two cases where cysts formed after a surgical procedure to make an opening in the sheath around the optic nerve.
Risk Factors and Frequency for Optic Nerve Cysts
The number of people who have cysts is hard to figure out because cysts can be caused by many different things and affect people of all ages. Another reason is that these cysts may not cause any symptoms so they never get diagnosed. This makes it tough to track. For instance, there have only been 31 documented cases of a condition called optic sheath meningocele according to a study by Lunardi and others.
Signs and Symptoms of Optic Nerve Cysts
Optic nerve cysts are a condition that some patients may have without even knowing, as it can sometimes cause no symptoms. Others may experience vague eye or neurological symptoms. In cases where these cysts are a type of cyst called arachnoid cysts, it can affect a person’s vision, which could be as good as perfect or result in no light perception at all.
Garrity and his colleagues reported on a group of thirteen patients who had a specific type of optic nerve cyst called optic nerve sheath meningocele. These patients experienced symptoms such as:
- Headaches
- Decreased vision
- Eye bulging
- Impaired pupil response to light
- Enlarged areas of visual field loss
- Swelling of the optic disc (the circular area at the back of the eye where the optic nerve connects)
- Twisted blood vessels at the optic disc
- Twisted veins in the retina
A colobomatous cyst is another type that often involves the optic nerve itself. As this lesion grows, commonly downwards, it might cause a feelable lump behind the lower eyelid. Sometimes, pulling down the lower eyelid may reveal a dark pigment to the mass, which is the color of the uvea – the middle layer of the eye. If a patient has this type of cyst in both eyes, they might also have systemic diseases such as chiasmal glioma, polycystic kidney, trisomy, or Edward syndrome.
Testing for Optic Nerve Cysts
If your doctor suspects you have a problem with your optic nerve or brain, they may use a special type of scan called an MRI (Magnetic Resonance Imaging). This will give them a detailed view of your brain and the muscles around your eye (called the orbit). Using this technology, they can identify any cysts (small fluid-filled sacs) inside your eye, see what they’re made of, and how they might be affecting other parts of your eye.
Depending on the specific type of cyst, an MRI scan can provide different information. Arachnoid cysts and meningoceles, which are specific types of cysts, usually show up as being the same density as the fluid found around the brain and spinal cord (known as CSF), and will appear dark in one type of imaging (T1) and bright in another (T2). These cysts do not usually “light up” when a contrast dye is used.
For a specific problem involving the lining around the optic nerve (optic nerve sheath meningoceles), scans may show the optic nerve and its protective ‘sheath’ becoming enlarged, forming a ring-like shape. Certain scan ‘angles’ can show more clearly the fluid-filled space and widening of the protective lining.
If your doctor suspects a problem with eye development in children, specifically a condition where the eye is smaller than normal (microphthalmos), an ultrasound might be used to examine the eye’s internal structure. It can be used to visualize any cysts in the eye. MRI, however, can offer a clearer view of the cyst’s contents, which are usually similar to eye jelly or brain and spinal cord fluid. MRI can also show the connection between the cyst, the nerve, and the eyeball. To evaluate your visual potential, or how well you could see after treatment, doctors may use something called retinal electrophysiology, a test that measures the electrical responses of your eye’s light-sensitive cells.
Treatment Options for Optic Nerve Cysts
The treatment for optic nerve cysts varies greatly, as these cysts can have different causes. Our current understanding of how to approach these cases largely comes from individual case studies or series of cases, as there isn’t any established consensus in scientific articles.
One concern about surgical removal or drainage of these cysts is the risk of damaging the optic nerve, which can have serious health consequences. Surgeons also need to be careful that the cyst isn’t part of an eye that has stable vision, as draining it could lead to loss of eye fluid.
There have been several interesting case studies over the years. For example in 1977, a patient with an arachnoid cyst in the optic nerve presented with symptoms like slight eye pain, blurry vision, and conditions such as significant optic disc edema (swelling in a part of the eye), and shallowing of the anterior chamber (the front part of the eye) in one eye. The patient was initially thought to have a type of tumor.
During a surgical procedure, doctors found a significant amount of cerebrospinal fluid (the fluid that surrounds the brain and spinal cord). The patient, unfortunately, lost sight in the affected eye nine months later, leading the doctors to recommend early diagnosis and drainage to preserve vision in such cases.
Case studies like these have shaped our understanding of how to approach optic nerve cysts. For another type of cyst known as optic nerve sheath meningoceles, some doctors suggest early surgical decompression (releasing pressure on the optic nerve) for patients who experience a quick drop in vision over 3 to 6 months. This approach has been associated with vision improvement and minimal downside.
On the other hand, there are cysts such as neuroepithelial cysts – this was the case for a 6-week-old baby who was treated successfully through surgery. Signs like eye protrusion and an abnormal pupillary light reflex showed improvement after surgery. It’s emphasized that the main goal is to prevent or reverse vision loss in these cases.
If the cyst is linked with an eye defect called coloboma and is causing cosmetic issues, it might be aspirated (drained of fluid). If the cyst keeps coming back, sometimes removing the eye and the cyst can be an option, and a prosthetic eye might be fitted.
What else can Optic Nerve Cysts be?
When diagnosing the cause of optic nerve problems, there are several conditions your doctor might consider. These could include:
- Optic nerve tumors, such as meningiomas and optic nerve gliomas
- Vascular malformations, which are abnormal clusters of blood vessels
- Systemic conditions like neurofibromatosis and Von Hippel Lindau, which can affect the entire body
If the optic nerve appears to be swollen on both sides, the doctor may also check for conditions that can increase the pressure of the fluid around your brain and spinal cord. These conditions could be due to a problem in the brain, a vascular issue, or a condition known as idiopathic intracranial hypertension, where the cause of the increased pressure is unknown.
What to expect with Optic Nerve Cysts
The results of surgical treatment compared to simple observation can differ greatly, as seen in various case reports and series. A study by Lunardi et al. found that out of 33 patients, 13 had surgery to drain optic nerve sheath meningoceles (a kind of small, fluid-filled sac on the optic nerve). Among these 13 patients, 5 experienced an improvement in their vision.
