Sympathetic nerve anatomy in the cavernous sinus and retrobulbar orbit of the cynomolgus monkey

We present new information regarding the sympathetic nerve anatomy in the cavernous sinus and retrobulbar orbit of the cynomolgus monkey. Postganglionic sympathetic nerves were identified using an immunoperoxidase technique in which the primary antiserum was directed against tyrosine hydroxylase, the rate-limiting enzyme in norepinephrine synthesis. Our work is unique in adapting this staining method to paraffin-embedded tissue. This technique allows sympathetic nerve fibers to be distinguished from other autonomic, sensory, and motor nerves. A large sympathetic nerve bundle lateral to the internal carotid artery in the cavernous sinus gave off one or more branches that leave the artery to encircle the abducens nerve. Further division occurs within the cavernous sinus, but all sympathetic nerve fibers destined for the orbit entered it through the superior orbital fissure. None pass through the optic canal. In the orbit, sympathetics were associated with the ophthalmic artery and some of its branches and with the sensory root to the ciliary ganglion. After entering the ganglion, the sympathetic fibers were lost to detection in most specimens, but they were again seen in a single short ciliary nerve in one instance. Sympathetic nerve fibers were not detected adjacent to several structures identified in the human anatomy literature, such as the intracranial and intracanalicular segments of the ophthalmic artery, the nasociliary nerve, the long ciliary nerves, the nerve to the inferior oblique muscle, or the lacrimal artery and nerve.