MRI restricted diffusion in lymphomatous optic neuropathy.

Restricted diffusion in the optic nerve detected with MRI has been previously reported in infarction and inflammation but not in infiltrative neoplasm. We report a 44-year-old man with recently diagnosed non-Hodgkin B-cell lymphoma who developed an acute left optic neuropathy. MRI showed no evidence of brain parenchymal or meningeal lymphoma but did show restricted diffusion in the intraorbital portion of the affected optic nerve. Despite treatment with corticosteroid, standard chemotherapy, and orbital X-irradiation, visual function did not improve. The restricted diffusion persisted on a follow-up MRI performed 4 months after the onset, a phenomenon that is atypical for infarction. Perhaps, this persisting imaging abnormality in lymphomatous optic neuropathy reflects the dense cellularity of the neoplasm.