The superior wall of the cavernous sinus: a microanatomical study.

The superior wall of the cavernous sinus was studied in 30 specimens obtained from 15 cadaver heads fixed in formalin. Trapezoidal in shape, the superior wall of cavernous sinus is limited laterally by the anterior petroclinoid ligament, medially by the dura of the diaphragma sellae, anteriorly by the endosteal dura of the carotid canal, and posteriorly by the posterior petroclinoid ligament. An interclinoid ligament bisects the wall, dividing it into two triangles: the carotid trigone anteromedially and the oculomotor trigone posterolaterally. Similar to the lateral wall of the cavernous sinus, the superior wall is formed by two layers: a smooth superficial dural layer and a thin, less defined deep layer. In the area of the carotid trigone, both layers separate to wrap the anterior clinoid process. The removal of this process will reveal a "clinoid space" medial to which the internal carotid artery can be identified. This clinoid segment of the artery, still extracavernous, is surrounded by two fibrous rings: a distal ring formed by fibers of the superficial dural layer and a proximal ring related to the deep dural layer. Below the proximal ring, the internal carotid artery becomes intracavernous; above the distal ring, the artery is continuous with its supraclinoid segment. The complex dural anatomy of the superior wall, its fibrous rings, and the clinoid space in relation to a superior surgical approach to the cavernous sinus are discussed.