Correct! The imaging features here suggest either an optic nerve sheath meningioma, a chronic dural inflammation (“pachymeningitis”), or lymphoma. You could order a CT scan, looking for calcium in the lesion, which would favor meningioma. You could look for inflammation or lymphoma elsewhere in the body with “pan CT scanning.” If a trial of prednisone improves vision, you would effectively exclude meningioma. In that case, additional imaging would be indicated to try to distinguish between the other options. X-irradiation of optic nerve sheath meningioma probably reduces the chances of lesion growth and further vision loss, and may even improve vision, but is not recommended if vision has already been severely compromised. Tip: do not recommend x-irradiation to prevent growth of an intracranial component because lesions that originate in the orbit almost never show sufficient intracranial growth to damage the other optic nerve or optic chiasm. Biopsy of this lesion is not advised because it is certain to damage vision. Recommend it only if all vision has been lost for many months and diagnosis is in doubt. Observation is an option if the patient refuses treatment despite understanding that x-irradiation is probably beneficial and has a low risk of harm. If x-irradiation is to be carried out, however, make sure that it is done in a center with experience treating such lesions, otherwise radiation toxicity to the retina, optic nerves, and optic chiasm is a serious risk!