Right lateral exposure of the cavernous sinus and associated neurovasculature. The dura over the lateral wall of the cavernous sinus and floor of the middle cranial fossa has been removed. The trigeminal nerve has crossed the apex of the petrous temporal bone and expanded as the Gasserian ganglion within Meckel's cave. The ganglion gives rise to its three divisions or branches. The ophthalmic nerve courses forward to enter the orbit via the superior orbital fissure. The maxillary nerve passes through foramen rotundum to enter the pterygopalatine fossa. The mandibular nerve passes through the foramen ovale to enter the infratemporal fossa. 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. The abducens nerve can be seen ascending along clival dura before penetrating it and coursing within the basilar plexus toward the petrous apex. It passes deep to the petroclinoid ligament (petrosphenoid or Gruber's ligament) traversing Dorello's canal to enter the cavernous sinus. Here, it passes along the lateral surface of the cavernous segment of the internal carotid artery (ICA). All four nerves enter the orbit through 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 and is 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. (Image courtesy of PA Rubino)