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the globe. The A-scan cross-section shows marked widening of the optic nerve defect within the orbital fat. The internal structure is regular and reflectivity is low (Fig. 3B).
HISTOPATHOLOGY
The histologic picture is that of a benign pilocytic (‘‘hair like’’) astrocytoma (Fig. 4). Elongated spindle-shaped astrocytes with uniform oval nuclei form intersecting bundles that distend the fibrous pial septa of the optic nerve. The astrocytes are cytologically benign and mitotic figures are not apparent. In most tumors, there are some astrocytes with spherical or cylindrical, swollen cell processes that stain brightly eosinophilic (‘‘Rosenthal fibers’’). There are usually pale cystic areas scattered among the astrocytes; these contain mucin (glycosaminoglycans) that can be highlighted using histochemical
Figure 4 (A) Intraoperative photograph of an optic nerve glioma.
(B) Gross and (C) Histologic features of an optic nerve glioma demonstrate expansion of the optic nerve by a loosely arranged pilocytic astrocytoma confined within the dural sheath.
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stains. Mucin may be particularly prominent in longstanding tumors. If the tumor infiltrates the surrounding meninges, then the astrocytes are accompanied by fibroblasts and meningothelial cells. Though not usually necessary for diagnosis, the astrocytic nature of the neoplasm can be immunohistochemically confirmed in paraffin sections using antibodies against glial fibrillary acidic protein (GFAP).
TREATMENT AND PROGNOSIS
There remains some controversy over the appropriate management of optic gliomas (6). Much of the debate results from a general lack of understanding of the natural history of this disease, and from small series of patients and short follow-up intervals. Nevertheless, it is clear that gliomas are true neoplasms with the potential for growth and spread into adjacent tissues, and therefore must be treated with this risk in mind.1
For lesions confined to the orbit with good vision and minimal proptosis, observation with serial MR imaging is appropriate. Visual loss is common, but typically stabilizes with time. If severe proptosis and blindness result, surgical excision should be considered for palliation and cosmesis. However, if the tumor remains stable, no specific therapy is necessary.
With documented posterior extension that threatens the chiasm, surgical excision should be considered because of the associated increased morbidity and mortality (Fig. 5). For large tumors already involving the chiasm, surgical debulking followed by adjunctive therapy may delay other CNS complications, but contralateral visual loss is a significant risk of any surgery. Although the data are inconclusive, radiotherapy may be effective in advanced cases but may cause major CNS morbidity in young children. Multiple agent chemotherapy for chiasmatic or recurrent tumors may delay progression. Preliminary studies are encouraging, but longer follow-up intervals and larger series will be needed before any firm conclusions can be drawn.
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Figure 5 Surgical excision of optic gliomas.
The prognosis for vision is variable. After initial visual deterioration seen in 80% of patients, vision tends to stabilize. In 26% of cases, vision remains better than 20=40, and in 45% better than 20=200. The prognosis for life depends on tumor location and involvement of adjacent structures. For orbital lesions, the prognosis for life is excellent, with a mortality rate less than 5%. With chiasmal involvement, mortality rises to 20%, from ultimate midbrain invasion. Once the hypothalamus or third ventricles are involved, mortality rises to 55% over 10 years.
REFERENCES
1.Dutton JJ. Gliomas of the anterior visual pathway. Surv Ophthalmol 1994; 38(5):427–452.
2.Garvey M, Packer RJ. An integrated approach to the treatment of chiasmatic–hypothalamic gliomas. J Neurooncol 1996; 28(2–3):167–183.
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3.Jakobiec FA, Depot MJ, Kennerdell JS, Shults WT, Anderson RL, Alper ME, Citrin CM, Housepian EM, Trokel SL. Combined clinical and computed tomographic diagnosis of orbital glioma and meningioma. Ophthalmology 1984; 91(2):137–155.
4.Haik BG, Saint-Louis L, Bierly J, Smith ME, Abramson DA, Ellsworth RM, Wall M. Magnetic resonance imaging in the evaluation of optic nerve gliomas. Ophthalmology 1987; 94(6): 709–717.
5.Ossoinig KC, Cennamo Byrne SF. Echographic differential diagnosis of optic nerve lesions. In: Thijssen JM, Verbeek AM, eds. Ultrasonography in Ophthalmology: Proceedings of the 8th SIDUO Congress. Dordrecht: Dr. W. Junk, 1981:327.
6.Listernick R, Louis DN, Packer RJ, Gutmann DH. Optic pathway gliomas in children with neurofibromatosis1: consensus statement from the NF1 Optic Pathway Glioma Task Force. Ann Neurol 1997; 41(2):143–149.