The Sellar and Periclinoidal Region. A, Superior view of the sellar region. The dura roofing the anterior clinoid process, optic canal, and lateral wall of the right cavernous sinus has been removed. The stump of a right superior hypophyseal artery has been preserved. An absent diaphragm exposes the upper margin of the pituitary gland. B, A dissector has been advanced below the falciform ligament into the optic canal. C, The anterior clinoid process has been removed while preserving the carotid oculomotor membrane and the proximal and distal dural rings. The optic strut and clinoid segment are exposed in the space created by removal of the anterior clinoid process. The dura forming the proximal and distal rings join on the outer wall of the artery to form a dural collar, the carotid collar, around the ICA. The carotid cave is positioned along the medial and posterior side of the ICA and extends downward between the distal dural ring and carotid collar and the outer wall of the artery. D, Posterior superior view. The proximal and distal dural rings converge as they extend along the posterior margin of the carotid where they blend into a single layer forming the diaphragm sellae. E, Lateral view of the proximal and dural rings. The proximal and distal dural rings converge posteriorly where both rings blend into the dural layer forming the diaphragm sellae. The clinoid segment of the carotid artery is surrounded by the carotid collar. F, Lateral view of the cavernous sinus and the proximal and dural rings. The distal dural ring is formed by the dura extending medially from the upper surface of the anterior clinoid process. The proximal ring is formed by the dura that separates the lower margin by the anterior clinoid from the oculomotor nerve and extends medially around the ICA. In this specimen, the mucosa lining the sphenoid sinus extends into the optic strut, and in some cases, the sinus may pneumatize through the strut into the anterior clinoid process. (Images courtesy of AL Rhoton, Jr.)