Optic Glioma

Optic glioma is a slow-growing brain tumor that develops along the optic nerve, the pathway that carries visual signals from the eye to the brain. While this is a serious condition, it has a high cure rate and primarily affects young children, with most cases diagnosed before the age of 5.

Table of contents

• What is optic glioma?
• Who is affected?
• Causes and risk factors
• Symptoms and warning signs
• How is optic glioma diagnosed?
• Treatment options
• Outlook and prognosis

What is optic glioma?

Optic glioma, also called optic pathway glioma or optic nerve glioma, is a type of brain tumor that forms in or around the optic nerve^[1]. The optic nerve is the vital connection between the eye and the brain that transmits visual information^[2].

These tumors are classified as pilocytic astrocytomas, which are considered low-grade and typically slow-growing^[3]. They can develop at various points along the visual pathway, including the optic nerve itself, the optic chiasm (where the left and right optic nerves cross), the optic tracts, or even extend into the hypothalamus, which is the hormone control center of the brain^[2].

As the tumor grows, it presses against the optic nerve, which can interfere with vision. The tumor can affect one or both eyes^[1]. Because these tumors are located near the base of the brain where hormones are controlled, they can sometimes affect the body’s endocrine functions, such as hormone production, salt and water balance, appetite, and sleep^[1].

optic pathway glioma, optic nerve glioma, juvenile pilocytic astrocytoma

Who is affected?

Optic glioma is rare and primarily a childhood condition. Nearly 75 percent of cases occur in children younger than 10 years old, with most children being younger than 5 at the time of diagnosis^[1]. It is rarely found in individuals over the age of 20^[7].

These tumors account for approximately 5 percent of all childhood brain tumors^[1]. They represent around half of all primary optic nerve tumor cases and 1.5 to 4 percent of all orbital tumors^[3].

Causes and risk factors

In most cases, the cause of optic glioma is not known. It’s important to understand that these and other brain tumors most often occur with no known cause. There is nothing that could have been done or avoided that would have prevented the tumor from developing^[1].

However, there is a strong link between optic glioma and a genetic condition called neurofibromatosis type 1 (NF1)^[2]. NF1 is a genetic disorder that causes tumors to form along nerves in the body. About 15 percent of children with NF1 will develop an optic pathway glioma^[1].

Interestingly, when optic glioma occurs in children with NF1, about two-thirds of the time, the tumor stops growing and disappears on its own without treatment^[1]. Because of this association, genetic testing for NF1 is recommended when a child is diagnosed with optic glioma^[3].

Symptoms and warning signs

The symptoms of optic glioma are caused by the tumor pressing against the nerves and nearby structures. Keep in mind that these symptoms may resemble other more common conditions or medical problems, such as needing glasses to correct poor vision. It is important to consult a physician for a proper diagnosis^[1].

The most common symptoms include:

• Vision problems, including vision loss that typically starts with loss of peripheral vision^[1]
• Proptosis, or eyeball protrusion, which occurs when the tumor pushes the eye outward from the socket. This is the most common sign, presenting in 95 percent of cases^[1][7]
• Squinting or difficulty with eye movement^[1]
• Involuntary eye movements^[2]

Additional symptoms may include:

• Headaches^[2]
• Nausea and vomiting^[2]
• Balance problems^[2]
• Hormonal problems, including abnormal growth and weight gain or loss^[1]
• Decreased memory and brain function^[2]
• Daytime sleepiness^[2]
• Loss of appetite and delayed growth^[2]

Children may also show symptoms of what doctors call diencephalic syndrome, which includes daytime sleeping, decreased memory, headaches, delayed growth, and loss of body fat^[2].

Blindness may occur, but only in about 5 percent of cases^[1]. Around 85 percent of people with optic nerve glioma will lose some of their vision, but over time, approximately 25 percent will retain vision between 20/20 and 20/40^[7].

How is optic glioma diagnosed?

The first step in diagnosis is forming an accurate and complete picture of the condition. Optic gliomas are typically diagnosed using a combination of imaging and vision testing^[1].

A neurological examination will typically show a loss of vision in one or both eyes. There may be changes in the optic nerve, including swelling or scarring of the nerve, or paleness and damage to the optic disc. There may also be signs of increased pressure in the brain^[2].

Tests that a doctor will likely order include:

• A complete physical examination^[1]
• Vision testing and eye examination^[1]
• Magnetic resonance imaging (MRI) of the brain and orbit to determine the tumor’s location and extent^[1][3]
• Computed tomography (CT or CAT) scan^[1]
• Testing for neurofibromatosis type 1 (NF1). If a child has NF1, vision is followed closely^[1]

It is very rare, below 5 percent of the time, for the glioma to move beyond the brain and spine. There is a blood brain barrier that serves to keep infections out and also ends up keeping tumors in^[1].

Biopsy is usually unnecessary for diagnosis, though advancements in molecularly targeted therapies may make genetic testing increasingly valuable^[3].

Treatment options

Treatment varies with the size of the tumor, its location, and the general health of the child. The goal may be to cure the disorder, relieve symptoms, or improve vision and comfort^[2].

Most children do not need to be treated right away. Because these tumors in children with NF1 grow very slowly, the decision to start treatment depends on the growth of the tumor and whether there has been a loss of vision or effect on the endocrine system^[10].

Chemotherapy

Chemotherapy is the use of drugs to destroy or slow the growth of cancer cells. It may be especially useful when the tumor extends into the hypothalamus or if vision has been worsened by the tumor’s growth^[2]. Chemotherapy remains the mainstay of optic nerve glioma treatment^[8].

Newer molecularly targeted therapies, such as mitogen-activated protein kinase kinase inhibitors and bevacizumab, represent a promising new treatment modality, and clinical studies are ongoing^[8].

Surgery

Surgery to remove the tumor may cure some optic gliomas. Partial removal to reduce the size of the tumor can be done in many cases. This will keep the tumor from damaging normal brain tissue around it^[2]. Some tumors are small enough that they can be removed in one surgery, but for many others, a staged approach is used, where part of the tumor is removed at first, then the remaining piece is shrunk using targeted chemotherapy or radiation before another surgery removes what is left^[11].

Radiation therapy

Radiation therapy may be recommended in some cases when the tumor is growing despite chemotherapy, and surgery is not possible. In some cases, radiation therapy may be delayed because the tumor is slow growing. Children with NF1 usually won’t receive radiation due to the side effects^[2].

Corticosteroids may be prescribed to reduce swelling and inflammation during radiation therapy, or if symptoms return^[2].

Monitoring

In some cases, careful monitoring is the best approach. The tumor must be watched closely, but normally, the growth of the tumor is very slow, and the condition remains stable for long periods^[2].

Outlook and prognosis

While these are serious tumors, they have a high cure rate^[1]. The outlook is very different for each person. Early treatment improves the chance of a good outcome. Careful follow-up with a care team experienced with this type of tumor is important^[2].

The survival rate is generally very good, right around 90 percent^[11]. Once vision is lost from the growth of an optic tumor, it may not return. However, total blindness is rare, only occurring in 5 percent of cases^[1][2].

Management of optic gliomas necessitates a multidisciplinary healthcare team, including neuro-ophthalmologists, oncologists, surgeons, geneticists, and support from psychologists. With evolving treatment options, the emphasis is on achieving an optimal prognosis for affected patients^[3].

Regular eye exams may allow early diagnosis of these tumors before they cause symptoms. Genetic counseling may be advised for people with NF1^[2].