Relationship of the Paraclival and Parasellar Internal Carotid Artery With the Cavernous Sinus and Meckel’s Cave. G, Close-up view of the posterosuperior compartment as well as the roof of the cavernous sinus. The dura of the posterior petroclinoid fold extending from the petrous apex to the posterior clinoid process is identified. The oculomotor nerve is seen entering the roof of the cavernous sinus. The trochlear nerve enters the roof posterolateral to that point and courses lateral and inferior to the oculomotor nerve initially. H, An endoscopic view looking from the bottom (midpetroclival fissure) up (roof of the cavernous sinus). The medial, posterosuperior, and posterior aspects of the lateral compartments of the cavernous sinus have been exposed. The third and fourth nerves are seen entering the roof as in G. The fifth nerve is passing more inferior toward Meckel’s cave. Finally, the interdural subsegment of the petrous segment of the abducens nerve is seen coursing obliquely between the 2 layers of the inferior petrosal sinus posterior to the paraclival ICA before it reaches the upper edge of the petrous apex. At the superior aspect of the petrous apex/petroclival fissure, the interdural subsegment transitions into the gulfar subsegment (asterisk) as it enters the sphenopetroclival venous gulf. Distal to the gulfar subsegment, the nerve enters the cavernous sinus and remains horizontal until it emerges below the parasellar ICA. I, An endoscopic panoramic view of the paraclival and parasellar ICA segments and their relationships to the nerves of the cavernous sinus and to Meckel’s cave. The parasellar ICA is medial to the nerves of the cavernous sinus and is most closely related to the distal cavernous subsegment of the abducens nerve. Some sympathetic fiber bundles are seen coursing along the surface of the ICA before they join cranial nerves VI and V1. J and K, Close-up view of the lateral compartment of the cavernous sinus. The oculomotor nerve courses immediately below the proximal dural ring toward the SOF. The trochlear nerve is seen ascending obliquely as it will eventually pass lateral to the oculomotor nerve toward the SOF and superior oblique muscle. The trigeminal V1 branch is at the inferior limit of the lateral wall of the cavernous sinus; it is flattened proximally and becomes more distinct toward the SOF. (Images courtesy of AL Rhoton, Jr.)