Background: Optic nerve gangliogliomas are extremely rate tumors of the central nervous system composed of elements of glial and neuronal origin. The clinical and biologic behavior of gangliogliomas depends on the glial component. Pilocytic gangliogliomas generally have a low growth rate and good ultimate prognosis. No definitive relation has yet been established between gangliogliomas and neurofibromatosis type 1.

Methods: The authors describe the clinical, histologic, and immunohistochemical features of an optic nerve ganglioglioma with several atypical findings. A review of the literature is provided.

Results: An optic nerve glioma was diagnosed in a 16-year-old patient who had signs of neurofibromatosis type 1; the atypical clinical course involved a rapid progression of symptoms with a significant increase in tumor size. The tumor was removed surgically and found to be a ganglioglioma composed of pilocytic glial cells (immunoperoxidase-positive for glial fibrillary acid protein) and neurons (immunoperoxidase-positive for neuron specific enolase, synaptophysin, and neurofilament). A focal astrocytic area showed increased cellularity, several mitotic figures, and an elevated labeling index with Ki-67 immunoperoxidase staining.

Conclusions: Optic nerve gangliogliomas are rare tumors that cannot be distinguished clinically from pilocytic astrocytomas. Although these tumors usually grow slowly, careful follow-up is advised. The atypical histologic features are considered to be a manifestation of rapid local growth rather than a harbinger of malignant behavior. The authors' findings suggest that gangliogliomas may be included in the diagnostic criteria for neurofibromatosis type 1.