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The most common primary tumors of the optic nerves and chiasm are those which arise from the glial stroma of the visual pathways. Growth of the neoplasms is slow but the natural course is an extension of the process with the production of blindness and often death. Since optic nerve gliomas are encountered infrequently, the effect of various forms of treatment is difficult to assess. It is the purpose of this paper to report, in summary, the case histories of 34 patients with primary glioma of the optic nerves and chiasm and to evaluate the use of radiation therapy and surgery in their management. Incidence and Pathology Optic nerve gliomas are tumors of young people. They are not, however, closely related to the highly malignant retinoblastoma, which also is a disease of early life. Optic gliomas are relatively uncommon, constituting only 1 to 2 per cent of all glial new growths (Martin and Cushing, 11; Lundberg, 10). The 34 cases to be reported here occurred during a period when approximately 2,000 surgically verified gliomas of all types were encountered in the Neurological Institute of New York. The incidence in the two sexes is essentially equal. Optic gliomas produce an expansion of the nerve or chiasm which may consist of a solitary fusiform enlargement or may form a solid irregular thickening along the entire course of the nerve. Localized enlargements often attain a diameter of 2.5 cm., and in some instances may be larger. The nerve sheath usually is not penetrated, although extraneural extension may sometimes occur in the late stages of growth. Tumors which arise within the orbital cavity may extend intracranially and vice versa. Extension results in erosion of the optic canal by pressure, and usually the canal becomes enlarged (Fig. 1), which is an important finding for roentgen diagnosis (Pfeiffer, 13). Radiologic evidence of such enlargement should be taken to indicate involvement of the intracranial portion of the nerve. Patients, when first seen, can for the most part be placed in one of three groups, depending on the gross pathological extent of the tumor. In some instances involvement is limited to one optic nerve throughout the course of the disease, because tumor growth may be self-limited. In other cases one optic nerve and the optic chiasm may be involved. The majority of our cases fall into this latter category. Examples of widespread intracranial extension of tumor may also be seen, even with ventricular obstruction and internal hydrocephalus. On section, the nerves and chiasm usually are found to be diffusely thickened. In some instances there may be a solid tumor nodule displacing the nerve eccentrically and compressing it into a crescentic form. Cystic degeneration may occur in the neoplastic tissue. The tumors ordinarily are not excessively vascular but in an occasional instance blood vessels are present in great numbers (Hudson, 9). A complete histologic description and a clear differentiation between gliomas and nerve sheath tumors was given by Verhoeff (16, 17). Disagreement still exists, however, among pathologists regarding the nature of the glial cells of which the tumor is composed. Some authors believe them to be unipolar and bipolar spongioblasts (Grinker, 7; Cuneo and Rand, 3). Others consider them to be predominantly piloid astrocytes, the elongated form resulting from a mechanical effect upon the cells as they grow in and among tight nerve bundles (Martin and Cushing; Wolf and Cowen, 19).
Taveras et al. (Sun,) studied this question.