• Most common infiltrative lesion of the optic nerve (ON).
• 1% of all intracranial tumors
• 3% of orbital tumors
• 4% of all gliomas
• Occurs in 15% of patients with NF1
• Represents 65% of intrinsic optic nerve tumors
• 90% recognized by second decade of life
• Also known as optic pathway glioma (OPG)
• Neurofibromatosis type 1 (NF1) in 25–30% of cases of OPG.
• Localized to chromosome 17 if associated with NF1 (autosomal dominant)
• Progressive growth with infiltration and compression of the ON, producing visual loss
– May affect ON anywhere along its course from globe through optic tract
• Neoplastic infiltration of ON
COMMONLY ASSOCIATED CONDITIONS
• NF1 present in 25–30% of OPG
• Progressive painless visual loss +/− proptosis and/or diplopia
• History of NF1
• Demonstrates features of an optic neuropathy: Decreased visual acuity, decreased color vision, nerve fiber bundle-type visual field defects though may have temporal defects or homonymous defect if concurrent involvement of the optic chiasm or tract respectively, afferent pupillary defect if unilateral or asymmetric optic nerve involvement
• Optic nerve may be pale or edematous based upon location of tumor with anterior involvement producing ON edema while posterior orbital, canalicular, or intracranial lesions demonstrate ON pallor
• May have proptosis, strabismus, or nystagmus
• May have stigmata of NF1 (e.g., Lisch nodules, café au lait spots, dermal neurofibromas)
Malignant transformation of an OPG essentially only occurs in patients who have previously undergone radiation therapy for their tumor.