Metrizamide demonstration of the subarachnoid space surrounding the optic nerves.

Intrathecal instillation of metrizamide has provided a useful tool for the in vivo evaluation of smaller structures adjacent to or within the subarachnoid cisterns. The authors report a case in which metrizamide filled the thin subarachnoid space surrounding the optic nerve in its course through the orbit. The finding appears to be infrequent, however, since it was not observed in any instance in a review of 80 metrizamide computed tomographic cisternograms in patients with normal intracranial pressure.