Abstract
A 23 year old man presented with transient visual obscurations and was found to have optic nerve edema and a thalamic lesion that did not enhance on magnetic resonance imaging. Lumbar puncture opening pressure was normal. Subsequent magnetic resonance images demonstrated optic nerve sheath enhancement. Pathological diagnosis of the thalamic mass was anaplastic astrocytoma (WHO grade III). Visual symptoms were attributed to spread of high grade parenchymal glioma to the optic nerve sheaths causing intraorbital optic nerve compression.