GLIOMAS OF THE ANTERIOR VISUAL PATHWAY

Gliomas of the anterior visual pathway are rare orbital lesions accounting for 65% of all intrinsic optic nerve tumors. These lesions occur principally among children in the first decade of life. They appear to be true neoplasms that characteristically show early growth, followed by stability in many patients. Visual prognosis is fair, and the outlook for life depends upon tumor location. When initially confined to the optic nerve alone, overall mortality is about 5%. Once the hypothalamus is involved, mortality rises sharply to over 50%. With involvement of the chiasm or hypothalamus, no form of therapy significantly alters the final outcome. Because of their indolent course, gliomas may be followed conservatively when confined to the optic nerve. In these cases, surgery is indicated only when blindness and pain or severe proptosis intervene. However, all such patients should be followed radiologically for evidence of posterior extension. When the chiasm is threatened, surgical excision via a craniotomy approach is warranted to prevent subsequent hypothalamic or third ventricle involvement. Malignant optic glioma is a distinct disease primarily affecting middle-aged adults. The chiasm is always involved, and although one eye may be spared initially, rapid progression to bilateral blindness is usual. The disease is uniformly fatal.