Stepwise Dissection of the Lateral Wall of the Right Cavernous Sinus. A, Lateral view showing the cavernous sinus sitting on the lateral surface of the body of the sphenoid bone medial to the temporal lobe. The oculomotor nerve penetrates the roof of the cavernous sinus by passing through the oculomotor triangle, which forms the posterior portion of the roof of the cavernous sinus. The anterior portion of the roof of the cavernous sinus sits below and medial to the anterior clinoid process. Removing the anterior clinoid exposes the clinoidal space and the anterior portion of the roof of the cavernous sinus but does not open into the venous spaces of the cavernous sinus. The nerves coursing in the lateral wall are barely visible through the dura. The inferior limit of the cavernous sinus is the superior border of V2. B, View showing small strip of the outer layer of dura covering the middle fossa floor removed to expose V2 and V3 coursing in the inner layer of dura in the lateral sinus wall and exiting the foramen rotundum and ovale. The superior petrosal sinus courses along the petrous ridge and opens into the cavernous sinus. C, View showing the anterior clinoid process and the outer layer of the lateral sinus wall back to the level of the gasserian ganglion removed. The inner layer of dura in which the nerves course in the anterior part of the lateral wall has been preserved. The dura covering the upper and lower surfaces of the anterior clinoid process extends medially to form the upper and lower dural rings. The clinoidal segment of the carotid, exposed by removing the anterior clinoid process, sits between the upper and lower dural rings. The optic strut separates the optic canal from the superior orbital fissure. The clinoidal segment of the carotid sits against the posterior surface of the optic strut and inferomedial to the anterior clinoid process. V1,V2, and V3 as well as the trochlear and oculomotor nerves can be observed through the semitransparent inner layer of the lateral wall. The supratrochlear triangle is located between the oculomotor and trochlear nerves, and the infratrochlear triangle (Parkinson’s triangle) is located between the trochlear nerve and the first division of the trigeminal nerve. The pericavernous venous plexus extends around V3. D, View showing the inner layer of the lateral sinus wall removed. The posterosuperior venous space of the cavernous sinus sits medial to the nerves and above the horizontal segment of the intracavernous carotid. The superior petrosal sinus, pericavernous venous plexus around V3, and superior ophthalmic vein open into the cavernous sinus. E–F, Photographs illustrating another stepwise dissection of another cavernous sinus. E, View showing the outer and inner layers of the lateral wall removed, with the venous contents of the sinus evacuated. The inferolateral trunk arises from the horizontal segment of the intracavernous carotid. The motor root of the trigeminal nerve passes through the foramen ovale on the medial side of the sensory root of V3. The anteromedial triangle is located between V1 and V2, and the anterolateral triangle is located between V2 and V3. F, View showing the anterior clinoid, with the oculomotor triangle opened. Removing the anterior clinoid process exposes the clinoidal space and the clinoidal segment of the carotid. The abducens nerve reaches the cavernous sinus by passing through Dorello’s canal and courses lateral to the posterior vertical segment of the intracavernous carotid and medial to V1 to enter the superior orbital fissure. The inferolateral trunk descends lateral to the abducens nerve. The anteroinferior venous space is located anterior and inferior to the posterior bend and horizontal segment of the intracavernous carotid. The oculomotor nerve divides into superior and inferior divisions just behind the superior orbital fissure. (Images courtesy of AL Rhoton, Jr.)