Optic nerve glioma classification
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2]
Overview
Optic nerve gliomas may be classified into two subtypes based on anatomic location, and whether or not they are associated with neurofibromatosis type 1.
Classification
Optic pathway gliomas (OPGs) are classified by whether or not they are associated with neurofibromatosis type 1 (NF1, von Recklinghausen's disease) and by anatomic location. According to their location along the optic pathway, the two major categories are: Location — Low-grade gliomas may involve the anterior visual pathway of the optic nerve (25 to 35 percent of cases) or the posterior visual pathways (chiasmal and postchiasmal).
Anterior visual pathway — Anterior tumors can be subdivided into:
- Orbital
- Intracanalicular
- Intracranial prechiasmal lesions.
Most of anterior visual pathway tumors are classified as pilocytic astrocytomas and they occur most frequently in prepubertal children. Neurofibromatosis type 1 tumors are more likely to invole anterior visual pathway. Posterior visual pathway — Posterior tumors may arise in the
- Optic chiasm
- Hypothalamus
- Anterior third ventricle
Most of posterior visual pathway tumors are classified histologically as pilocytic astrocytomas, and occasionally gangliogliomas. Hypothalamic and chiasmal lesions present at a mean age of about three years. Optic nerve gliomas without an association with neurofibromatosis type 1 are more frequent in the posterior visual pathway.
Optic nerve gliomas can involve one or both optic nerves. About 10% of optic pathway tumors are located within an optic nerve, one third of the tumors involve both optic nerve and chiasm, another one third involves predominantly the chiasm itself, and one fourth involves predominantly the hypothalamus. 5 5% of optic nerve gliomas are multicentric. In approximately 50% of patients, optic nerve gliomas occurs without any known chromosomal aberration. In the remaining 50% of patients, a diagnosis of neurofibromatosis type 1 is seen. NF-1 is an autosomal dominant disorder with an incidence of one in 3000-5000 births. In children diagnosed with NF-1, about 10% develop optic gliomas, and 25-40% of optic gliomas occur in children with NF-1.