Optic Pathway Tumor

Other names/subtypes: optic nerve tumor, chiasmatic glioma, optic glioma

What is Optic Pathway Tumor?

Optic pathway tumor is a type of glioma, a tumor that grows from glial cells which surround and support nerve cells. Optic pathway tumors in children are usually low-grade tumors. They grow along structures of the visual system including the optic nerve, optic tract, and/or optic chiasm.

As the tumor grows, pressure on the visual system structures can cause vision problems. Optic pathway gliomas can also develop near the pituitary gland and hypothalamus. Depending on the location, the tumor may affect endocrine function and hormone production.

Optic pathway tumors account for up to 5% of all pediatric central nervous system (CNS) tumors. They are most common in younger children and in children with neurofibromatosis type 1 (NF1).

Treatment for optic pathway tumor depends on factors such as age, vision, NF1 status, and location of the tumor. Surgery, chemotherapy, and/or radiation therapy may be used to treat optic pathway tumors. However, treatment is complex due to potential harm to vision and endocrine function. Some patients may be followed with observation to see how the disease progresses.

Signs and Symptoms of Optic Pathway Tumor

Symptoms of optic pathway tumor depend on several factors including:

Child’s age and stage of development
Size of the tumor
Location of the tumor

Optic pathway tumor signs and symptoms may include:

Vision and eye problems:
- Vision loss
- Decrease in color vision
- Bulging or forward position of the eye (proptosis)
- Crossed eye (strabismus)
- Swelling or atrophy of the optic disc
- Decrease in visual field or area of vision
Head tilt
Unusual eye movements
Hormone disturbances resulting in change in appetite, weight, sleep, growth, or other endocrine problems

Diagnosis, Tests, Procedures

Doctors evaluate optic pathway tumors in several ways.

A health history and physical exam helps doctors learn about symptoms, general health, past illness, family history, and risk factors. Genetic testing may be performed to check for inherited conditions that increase risk for certain tumors. Blood chemistry and hormone studies are used to look at substances in the blood and urine.
- Most optic pathway gliomas occur in children under 10 years of age. The inherited condition neurofibromatosis type 1 (NF1) increases risk for these tumors. About 15-20% of children with NF1 develop optic pathway tumors.
Comprehensive tests of endocrine function will be performed if the tumor is close to the pituitary gland.
A neurological exam measures different aspects of brain function including memory, vision, hearing, muscle strength, balance, coordination, and reflexes.
A comprehensive eye exam is used to evaluate different aspects of visual function including appearance of eye structures, visual acuity, visual field, and color perception.
Imaging tests are used to help identify the tumor, see how big the tumor is, and find out what brain areas may be affected.
- Magnetic resonance imaging (MRI) uses radio waves and magnets to make detailed pictures of the body. The images made by MRI can give more information about the type of tumor and the potential spread of disease. This is the main imaging method to evaluate optic pathway glioma.
- Computed tomography (CT scan) uses X-rays to create cross-sectional images of the organs and tissues inside the body. The machine takes many pictures to make a very detailed image. The images are taken as a series of “slices” of the body and are saved to a computer.
A biopsy is usually used to diagnose optic pathway tumor when imaging and history are not diagnostic. In a biopsy, a small sample of the tumor is removed during surgery. A pathologist looks at the tissue sample under a microscope to identify the specific type and grade of tumor.

Grading and Staging of Optic Pathway Tumors

Optic pathway tumors are grouped by how they look under the microscope. The more abnormal tumor cells look, the higher the grade. Most optic pathway tumors in children are low grade. The cells don’t look much different from normal cells and grow slowly. They are less likely to spread to other parts of the CNS.

Rarely, pediatric optic pathway tumors may be high grade. These tumors are more aggressive, grow quickly, and can spread throughout the brain and spinal cord.

Prognosis for Optic Pathway Tumors

The long-term survival rate for pediatric optic pathway tumor is high (>90%). Children with NF1 may have slow growing tumors that can be followed with observation. Despite the high survival rate, treatment and management of these tumors is complex. Vision problems are common in survivors of optic pathway glioma. Depending on the location of the tumor, endocrine function may also be affected. A multidisciplinary care team is needed to plan treatments to balance cure and quality of life.

Factors that influence prognosis include:

Child’s age at diagnosis
Type and grade of the tumor
Whether the cancer is localized or has spread to other areas of the brain
If surgery can completely remove the tumor
Presence of an inherited condition that increases risk for cancer such as NF1
If the cancer is new or if it has come back (recurrent)

An early diagnosis helps preserve vision and eye health. The sooner that pressure on the visual system structures can be relieved, the more likely it is that vision will improve.

Treatment of Optic Pathway Tumor

There is no single treatment plan for optic pathway tumor. Because these are usually low grade tumors, preserving meaningful vision is a main concern. The therapies used to treat optic nerve glioma depend on the age of the child, extent of vision loss, location and size of the tumor, and whether the child has NF1.

Treatment options include:

Doctors monitor patients using eye exams and periodic MRI scans. Indications of disease progression include worsening vision, increase in tumor size, or spread of disease.

Surgery may be performed to remove as much of the tumor as possible. However, surgery alone may not provide a cure. In some cases, surgery is not possible due to the location of the tumor. Risks of surgery include worsening of vision and potential harm to nearby structures including the hypothalamus.
Chemotherapy is often used to treat optic pathway tumors. It is especially useful in treating younger patients to delay or avoid radiation therapy. It may also be used when surgery is not a good option, or when surgical removal of the tumor is not complete. However, not all tumors respond to chemotherapy.

Chemotherapy-associated hearing loss is an important consideration in planning treatments. This is always an important risk to consider. However, patients with optic pathway tumor have the additional burden of potential vision impairments, so avoiding hearing loss is particularly important.

There is no single chemotherapy plan that is used for all optic pathway gliomas. The medical team will decide the most appropriate plan for the patient given the type and location of tumor, symptoms, patient age, and other factors. Some chemotherapy drugs used in the treatment of this cancer include vincristine, carboplatin, vinblastine, lomustine, and temozolamide.
Targeted therapies work by acting on, or targeting, specific features of tumor cells. In some tumors, there are gene changes in the proteins that control tumor cell growth and division. Certain drugs are being tested to see if they can block the signals that promote the growth of cancer cells. These include MEK protein inhibitors trametinib and selumetinib. V600E BRAF inhibitors vemurafenib and dabrafenib are also being studied.

In some optic pathway gliomas, there appears to be a change in the BRAF gene in cells of the tumor. This change is called a V600E BRAF mutation. The BRAF gene helps to control a protein important for cell growth and function. Certain drugs can block this specific signaling pathway. These V600E BRAF inhibitors include vemurafenib and dabrafenib. This mutation is not as common in optic pathway gliomas; less than 10% of patients have this gene change.
Radiation therapy may be used for older children depending on the type of tumor and its location. In optic pathway tumor, radiation therapy is the most effective treatment and helps to preserve vision. However, there is a risk of late effects, especially for younger patients.

Life after Optic Pathway Tumor

Periodic imaging tests and comprehensive eye exams are used to monitor patients long-term. Multidisciplinary care may include a variety of speciality areas including rehabilitation, neurology, and endocrinology. Eye health is particularly important for all survivors of optic pathway tumor. Eye exams at least once a year by an ophthalmologist are recommended as part of routine health care. Many children have lifelong vision impairments, and vision assistance may be needed. Low vision specialists and school accommodations can assist children in adapting to vision losses. Protective eyeglasses should also be worn to prevent eye injury.

More: Life After Brain Tumors

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Reviewed: June 2018