The neural tumors that may involve the orbit include optic nerve gliomas, neurofibromas, meningiomas, and schwannomas.
Optic Nerve Glioma
Optic nerve gliomas are uncommon, usually benign tumors that occur predominantly in children in the first decade of life (Fig 5-9). The chief clinical feature is gradual, painless, unilateral axial proptosis associated with vision loss and an afferent pupillary defect. Other ocular findings may include optic atrophy, optic nerve head swelling, nystagmus, and strabismus. The chiasm is involved in roughly half of cases of optic nerve glioma. Intracranial involvement may be associated with intracranial hypertension as well as decreased function of the hypothalamus and pituitary gland. Up to half of optic nerve gliomas are associated with neurofibromatosis (NF). In patients with NF, the gliomas often proliferate in the subarachnoid space, while those occurring in patients without NF usually expand within the optic nerve substance without invading the dura mater.
Optic nerve gliomas can usually be diagnosed by means of orbital imaging. CT and MRI typically show fusiform enlargement of the optic nerve, often with stereotypical kinking of the nerve. MRI may also show cystic degeneration, if present, and may be more accurate than CT in defining the extent of an optic canal lesion and intracranial disease.
Figure 5-9 Optic nerve glioma. A, Right optic nerve glioma. The patient has severe proptosis with exposure and light perception vision. B, Funduscopic view. Note swollen optic nerve head with obscured margins. C, T2-weighted axial MRI shows glioma extending into the optic canal. D, Sagittal MRI shows a heterogeneous mass (arrows) in the apex of the orbit.
(Parts A, C, and D courtesy of Raymond Douglas, MD; part B courtesy of Roger A. Dailey, MD.)
Because neuroimaging is frequently diagnostic, it is usually unnecessary to perform a biopsy of a suspected lesion. Moreover, obtaining tissue from an appropriate site may be challenging: biopsy of the optic nerve itself may produce additional loss of visual field or vision, while a specimen from a too-peripheral portion of the nerve may inadvertently capture reactive meningeal hyperplasia adjacent to the glioma and lead to a misdiagnosis of fibrous meningioma. Gross pathology of resected tumors reveals a smooth, fusiform intradural lesion. On microscopic examination, benign tumors in children are considered to be juvenile pilocytic (hairlike) astrocytomas. Other histologic findings include arachnoid hyperplasia, mucosubstance, and Rosenthal fibers (see the discussion of the pathologic features of glioma in BCSC Section 4, Ophthalmic Pathology and Intraocular Tumors).
Malignant optic nerve gliomas (glioblastomas) are very rare and tend to affect adult males. Initial signs and symptoms of malignant gliomas include severe retro-orbital pain, unilateral or bilateral vision loss, and, typically, massive swelling and hemorrhage of the optic nerve head (pallor may also be observed with posterior lesions). Despite treatment, including high-dose radiotherapy and chemotherapy, these tumors usually result in death within 6–12 months.
The treatment of nonmalignant optic nerve gliomas is controversial. Although most cases remain stable or progress very slowly, leading some authors to consider them benign hamartomas, the occasional case behaves aggressively. There are rare reports of spontaneous regression of optic nerve and visual pathway gliomas. Cystic enlargement of the lesions leading to sudden vision loss can occur even without true cellular growth. A treatment plan must be carefully individualized for each patient. Factors affecting therapeutic decisions include the tumor’s growth characteristics, extent of optic nerve and chiasmal involvement as determined by clinical and radiographic evaluation, vision in the involved and uninvolved eyes, presence or absence of concomitant neurologic or systemic disease, and history of previous treatment. The following options may be considered.
Presumed optic nerve glioma, particularly with good vision on the involved side, may be carefully followed if the radiographic evidence is characteristic of this type of tumor and the glioma is confined to the orbit. Because visual function does not directly correlate with glioma size or growth, follow-up should include precise measurements of optic nerve function in addition to serial imaging studies. Many patients maintain good vision and never require surgery.
Rapid intraorbital tumor growth may prompt surgical resection in an effort to isolate the tumor from the optic chiasm and thus prevent chiasmal invasion. To obtain tumor-free surgical margins, the surgeon uses a transcranial approach. Surgical excision of a tumor confined to the orbit may also be considered if it causes severe proptosis with corneal exposure or unacceptable cosmesis. Removal through an intracranial approach may also be indicated at the time of initial diagnosis or after a short period of observation if the tumor involves the prechiasmal intracranial portion of the optic nerve. Complete excision is possible if the tumor ends 2–3 mm anterior to the chiasm.
Combination chemotherapy using dactinomycin, vincristine, etoposide, and other agents has been reported to be effective in patients with progressive chiasmal-hypothalamic gliomas. Chemotherapy may delay the need for radiation therapy and thus reduce deleterious effects on long-term intellectual development and endocrine function in children. However, chemotherapy may carry long-term risks of blood-borne cancers.
Radiation therapy is typically considered if the tumor cannot be resected (usually lesions of the chiasm or optic tract) and if symptoms, particularly neurologic, progress after chemotherapy. It may also be considered after surgical excision if reliable radiographic studies document subsequent growth of the tumor in the chiasm or if chiasmal and optic tract involvement is extensive. Because of potentially debilitating adverse effects (including intellectual disability, growth retardation, secondary tumors, and malignant transformation within the radiation field), radiation is generally reserved as a last resort for children who have not completed growth and development.
See additional discussion of optic nerve glioma in BCSC Section 5, Neuro-Ophthalmology.
Glass LR, Canoll P, Lignelli A, Ligon AH, Kazim M. Optic nerve glioma: case series with review of clinical, radiologic, molecular, and histopathologic characteristics. Ophthalmic Plast Reconstr Surg. 2014;30(5):372–376.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.