Intrathecal metrizamide enhancement of the optic nerve sheath.

The subarachnoid space continues into the orbit as part of the optic nerve sheath. This space varies in size but is usually tiny. Occasionally, prominent (one case in our experience) enhancement of the optic nerve as part of metrizamide computed tomography (CT) cisternography is seen on transverse and coronal scans presumably because of a patulous optic subarachnoid space. In five cases, we have appreciated minimal enhancement of optic nerves with metrizamide only by close comparison of CT numbers with base-line scans. One of these patients had a tiny meningioma removed successfully from the optic sheath, with return to normal vision of a previously blind eye.