Optic Nerve Glioma

In contrast to that found in adults, optic nerve gliomas in children are benign. However, it is visually threatening because the tumors can occur anywhere along the optic nerve, chiasm or optic tract. More commonly, they involve the optic chiasm, the part of the visual system where the neurons of both optic nerves cross. The tumor eventually replaces the normal architecture of the nerves. Optic nerve glioma represents 2/3 of all primary optic nerve tumors and is commonly seen in children younger than 10 years of age.

Optic nerve and chiasmal gliomas are slow-growing, and patients may present with different symptoms. The most common presentation is visual loss, which is usually bilateral, when the chiasm is involved. Other findings include optic nerve atrophy, strabismus, nystagmus and proptosis. Posteriorly located tumors can present with diabetes insipidus, hyperactivity, hypotension, hypoglycemia, or simply failure to thrive after a period of normal growth.

There is an important association between optic nerve glioma and neurofibromatosis. Approximately 10-70% is associated to neurofibromatosis type 1. Likewise, approximately 15% of neurofibromatosis patients will develop optic nerve gliomas. Compared to patients without neurofibromatosis type 1, the tumor progression is slower, vision fluctuation is common, visual prognosis is good, but life expectancy is shorter, in patients with neurofibromatosis type 1.

The classic fusiform enlargement of the optic nerve can be documented by CT scan. However, MRI (particularly T2-weighted) is considered the best modality to evaluate tumor anatomy in relation to other important cranial structures.

Obtaining serial ocular examinations and neuroimaging are important to monitor the tumor progression. Neuroimaging should be performed every 6 months and visual acuity with visual field testing at approximately 3 month intervals, at least for the first year after diagnosis. The NF1 Optic Pathway Glioma Task Force has recommended annual screening, including neuroimaging, for children with asymptomatic NF1 until age 6 and examinations every 2 years thereafter.

The treatment of optic nerve gliomas remains controversial because the natural history is unknown. Some studies indicate that 50% show progressive enlargement with visual loss. Progressive visual loss and enlargement of the tumor are indications for therapy.

If the tumor is localized in one optic nerve, many advocate sacrificing vision, by surgical removal of the optic nerve. This is done to prevent involvement of the chiasm and the more posterior structures.

There is no single accepted indication for treatment of chiasmal glioma. If there is involvement of the hypothalamus or third ventricle or gross enlargement of the optic tract, treatment by radiotherapy is 50% effective in controlling the disease. In children younger than 4 years of age, chemotherapy with vincristine and carboplatin is often preferred over radiation therapy. Chemotherapy may delay radiation; however, about 60% of these children eventually relapse.