Optic Glioma

Diagnosis Definition

• Optic glioma is the most common primary neoplasm of the optic nerve
• The optic chiasm, optic tracts, and optic radiations can be involved
• The tumors are usually benign in children and aggressive in adults; 90% present before age 20
• Adults can get optic nerve glioblastomas, whereas optic gliomas are a disease of childhood and neurofibromatosis type 1 (NF1)
• Optic gliomas are usually unilateral except in patients with NF1; up to 20% of patients with NF1 have optic gliomas

Imaging Findings

• MRI is better than CT for evaluating the optic nerve, optic chiasm, and optic radiations
• MRI shows tubular or fusiform enlargement of the optic nerve, with kinking or buckling
• Optic gliomas are typically isointense to cortex and hypointense to white matter and orbital fat on T1; they are isointense to hyperintense relative to white matter and the cortex on T2; intense enhancement is common, although optic nerve glioblastomas in adults may only minimally enhance as they are low grade astrocytomas
• The bony optic canal may be widened if the intracanalicular segment of the nerve is involved
• If associated with NF1, hyperintense lesions can be seen in the cerebellum, brain stem, basal ganglia, thalamus, periventricular white matter, and corpus callosum without mass effect, edema, or enhancement

KEY IMAGES

Pearls

• Optic glioma can be diagnosed with a high degree of confidence when it involves the optic chiasm and retrochiasmatic optic pathway
• Although MRI is the ideal imaging modality to evaluate the optic nerve, CT is better at showing erosion or expansion of the optic canal
• Meningioma, the primary differential diagnostic consideration, is characterized by peripheral enhancement of the optic nerve sheath (aka, “tram-track” sign), whereas enhancement of optic gliomas is more uniform
• Calcification, seen in meningiomas but not gliomas, is best seen on CT

References

1. Smith MM, Strottmann JM. Imaging of the optic nerve and visual pathways. Semin Ultrasound CT MR 2001; 22(6):473-487