Stepwise Dissection of the Posterior Wall of the Cavernous Sinus. A, Posterior view showing the posterior wall of the cavernous sinus. The posterior wall of the cavernous sinus sits between three points: the posterior clinoid process, the site where the abducens nerve pierces the dura of the clivus, and the medial aspect of the trigeminal porus. The abducens nerve has an upward course after piercing the dura of the clivus and passing through Dorello’s canal. The oculomotor nerve penetrates the roof of the cavernous sinus in the middle of the oculomotor triangle. The superior petrosal sinus courses along the petrous ridge and above the posterior root of the trigeminal nerve. The inferior petrosal sinus courses along the petroclival fissure and opens around the abducens nerve into the basilar sinus. The part of the right petrous apex below the trigeminal porus has been removed to expose the petrous carotid. B, View showing the clival dura opened to expose the basilar sinus, the largest communication between the cavernous sinuses. The petrosphenoid ligament (Gruber’s ligament), which roofs Dorello’s canal, extends from the petrous apex to the lower part of the lateral edge of the dorsum sellae. The lateral limit of the posterior wall of the cavernous sinus is the medial aspect of the trigeminal porus. C, View showing part of the basilar sinus evacuated to demonstrate the upward course of the abducens nerve after piercing the clival dura. (Images courtesy of AL Rhoton, Jr.)