Optic Pathway Glioma

What is an optic pathway glioma?

An optic pathway glioma (OPG) is a term often used for a type of tumor that forms in the brain regions involved in vision (the visual system). These tumors are a type of low-grade glioma and are most often classified as pilocytic astrocytomas.

"Optic pathway glioma" is no longer the official term for this tumor, but it is still commonly used by doctors, patients, and their families.

OPGs in children grow slowly. But as the tumor grows, pressure on the visual system can cause vision problems. OPGs can also form near the pituitary gland and hypothalamus. Depending on the location, the tumor may affect hormone production.

OPGs make up 5% of all pediatric central nervous system (CNS) tumors. They are most common in young children and children with neurofibromatosis type 1 (NF1).

Treatment for an OPG depends on your child’s age, vision, NF1 status, and tumor location. Treatments may include surgery, chemotherapy, radiation therapy, and targeted therapy. Treatment is complex because the doctors want to avoid harming vision and endocrine function.

Doctors may watch patients over time to see how their disease progresses.

Symptoms of optic pathway glioma

Symptoms of an OPG depend on:

• Child’s age and stage of development
• Tumor size
• Tumor location

OPG signs and symptoms may include:

• Vision and eye problems:
  • Vision loss
  • Decrease in color vision
  • Bulging eye, also called proptosis
  • Crossed eye, also called strabismus
  • Swelling or shrinking of the optic disc
  • Decrease in visual field or area of vision
• Head tilt
• Unusual eye movements
• Hormone disturbances that may cause change in appetite, weight, sleep, growth, or other endocrine problems

Risk factors for optic pathway glioma

Most OPGs occur in children under the age of 10. These tumors are closely linked to neurofibromatosis type 1 (NF1). Children with NF1 need regular eye exams.About 20% (2 in 10) of children with NF1 may develop an OPG.  

Children with NF1 should be evaluated in a major treatment center for correct diagnosis and treatment. Some lesions in NF1 may be confused as glioma, or children may have slow-growing tumors that can be followed with observation. 

Diagnosis of optic pathway glioma

Tests to diagnose optic pathway gliomas may include:

• A physical exam and health history to learn about symptoms, general health, past illness, and risk factors.
• An eye exam to check eye health and vision.
• A neurological exam to measure brain function. This includes memory, vision, hearing, muscle strength, balance, coordination, and reflexes.
• Endocrine tests to measure hormone function, espeically if the tumor is near the pituitary gland.
• Imaging tests to help identify the tumor, its size, and location. These tests could include magnetic resonance imaging (MRI) and computed tomography (CT scan)
• A biopsy to look at a sample of the tumor under a microscope to identify the type of tumor.
• Genetic and molecular testing of the tumor to find specific changes (mutations) in tumor cells. These changes help doctors make the correct diagnosis and choose the best treatment.  

Stages of optic pathway glioma

Most OPGs in children are low grade. The cells of a low-grade tumor:

• Grow slowly
• Do not look much different from normal cells
• Are less likely to spread to other parts of the body

Rarely, OPGs in children may be high grade. High-grade tumors:

• Are more aggressive
• Grow quickly
• Can spread throughout the brain and spinal cord

Treatment of optic pathway glioma

There is no single treatment plan for OPG. Because these are usually low-grade tumors, protecting vision is a main concern. Treatment options include observation, surgery, targeted therapy, chemotherapy, and radiation.

Testing of the tumor helps to get the right diagnosis and find the best treatment. But if the tumor is in the nerve behind the eye, doctors must decide if it is safe to get a sample of the tumor for testing or if it should be treated without a biopsy.

Therapies depend on:

• Age of the child
• How much vision was lost
• Tumor location and size
• Whether the child has NF1

Observation of optic pathway glioma

Doctors monitor patients using eye exams and regular MRI scans.

If the disease worsens, the patient may have more vision problems, the tumor may grow larger, or the disease may spread.

Surgery for optic pathway glioma

Surgery is sometimes used to help in the diagnosis and treatment of optic pathway gliomas. Surgery may be done to remove as much of the tumor as possible. Complete removal of the tumor may not be possible, so surgery alone may not provide a cure. 

In some cases, doctors may avoid surgery because of the tumor’s location. Risks of surgery include worsening of vision or damage to nearby structures, such as the visual system, pituitary gland, or hypothalamus. Surgery is used less often in patients with NF1.

Targeted therapies for optic pathway glioma

Studies show that most low-grade gliomas have specific genetic mutations in the tumor cells. These gene changes can usually be treated with special medicines called targeted therapies. Targeted therapies work by acting on, or targeting, specific features of tumor cells. In some tumors, there are changes in the genes and proteins that control tumor cell growth and division. Scientists are testing drugs to see if they can block the signals that cause certain cancer cells to grow.

In optic pathway gliomas, changes in the BRAF gene are common. These mutations often occur as a BRAF fusion/duplication or a BRAF V600E mutation. There are drugs that target the BRAF V600E mutation and drugs that target BRAF fusion/duplication (MEK inhibitors). In patients with NF1, the gene mutation is in NF1 gene, and in these cases, MEK inhibitors are used.

Targeted therapies are changing how doctors treat optic pathway gliomas that cannot be completely removed. New medicines that target tumor cells can treat tumors with fewer side effects than traditional chemotherapy or radiation. So, these targeted therapies are becoming the first choice for treatment.

Chemotherapy for optic pathway glioma

Chemotherapy is often used to treat OPGs. It is used in younger patients to delay or avoid radiation therapy. It may also be used when surgery is not a good option or if surgery cannot remove the tumor completely. Not all tumors respond to chemotherapy.

Hearing loss may be a side effect of some type of chemotherapy. Your care team will consider this risk when planning treatments. Patients with OPGs may have vision problems, so avoiding hearing loss is important.

No single chemotherapy plan is used for all OPGs. The medical team will figure out the best plan based on your child’s needs. The plan will depend on factors such as:

• The tumor’s location
• Symptoms
• Your child’s age
• Genetic changes

Some chemotherapy drugs used to treat OPG include vincristine, carboplatin, vinblastine, and lomustine.

Radiation therapy for optic pathway glioma

Radiation therapy may be used for older children depending on the type of tumor and its location. In OPG, radiation therapy is the most effective treatment and helps preserve vision. But there is a risk of late effects, especially for younger patients.

Prognosis for optic pathway glioma

The long-term survival rate for childhood OPG is high (above 90% or 9 in 10) in the United States. But treatment and management of these tumors is complex. Vision problems are common in survivors. Depending on the tumor location, endocrine function may also be affected.

A pediatric cancer care team will need to plan treatments. They will balance cure and quality of life. Every case is different. Ask your care provider for information about your child’s treatment and prognosis.

Prognosis depends on such factors as:

• Your child's age at diagnosis
• Type and grade of the tumor
• Genetic mutations in the tumor
• If the cancer has spread
• If surgery can completely remove the tumor
• Inherited conditions that increase risk, such as NF1
• Whether the cancer is new or has come back

Early diagnosis helps preserve vision and eye health.

Support for optic pathway glioma

Doctors use imaging tests and eye exams to monitor patients long-term. Follow-up care may include specialty areas such as rehabilitation, neurology, and endocrinology.

Eye health is important for survivors of OPGs. Your child should visit an ophthalmologist (eye doctor) at least once a year as part of routine health care. Many survivors have lifelong vision problems, and vision assistance may be needed. Low-vision specialists and school accommodations can help children adapt to vision loss. Protective eyeglasses can help prevent eye injury.

Questions to ask your care team

• What type of tumor does my child have?
• Does the tumor have any gene mutations or alterations?
• What are the treatment options for this type of optic pathway glioma?
• What are the possible side effects of each treatment?
• What can be done to manage side effects?
• How will the tumor or treatment affect my child's vision?
• How often will my child need scans or vision tests?

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