Right superior view of the cavernous sinus and associated neurovasculature. The dura over the roof and lateral wall of the cavernous sinus has been removed as has the anterior clinoid process of the sphenoid bone. The optic nerve courses into the optic canal with the ophthalmic artery, a branch off the C6 (ophthalmic) segment of the internal carotid artery (ICA). The oculomotor nerve is shown here entering the roof of the cavernous sinus. It lies superior to the trochlear nerve. The trochlear nerve courses along the lateral wall of the cavernous sinus superior to the ophthalmic nerve, a sensory branch of the trigeminal nerve that leaves the Gasserian ganglion. All three nerves course forward to enter the orbit via the superior orbital fissure. The inferolateral trunk is a lateral arising branch of the C4 (cavernous segment) of the ICA that supplies blood to the oculomotor, trochlear, and abducens nerves as well as to the Gasserian ganglion. The C5 or clinoid segment of ICA is delimited by the proximal and distal dural rings. The proximal ring forms the roof of the cavernous sinus and is continuous with the dura covering the inferolateral aspect of the anterior clinoid process (cut). The distal ring is another layer of dura that is continuous with the dura covering the superomedial aspect of the anterior clinoid process to the falciform ligament overlying the optic nerve and also continuous with the tuberculum sellae (not labeled). The two rings fuse posteriorly but are variably separated anteriorly. The postganglionic perivascular sympathetic plexus is demonstrated on the surface of the ICA (not labeled). (Image courtesy of PA Rubino)