Endocranial and Exocranial Landmarks for the Sella and Parasellar Region. A, Endoscopic endonasal view of the sellar wall of the sphenoid sinus. The lateral opticocarotid recess extends into the optic strut in most specimens. The lateral aspect of the distal dural ring is located approximately 1 mm above the tuberculum recess and is medially continuous with the diaphragm attachment that is located at the level or slightly inferior to this recess (blue line). The proximal dural ring is located along the inferior border of the lateral opticocarotid recess and its projection extends medially toward the tuberculum recess (yellow dotted line). The middle clinoid when present (green shadowed area, green dotted lines) protrudes inside the cavernous sinus toward the anterior clinoid inferior and lateral to the medial opticocarotid point (point 4) and caroticosellar point (point 5). The caroticoclinoid ligament (light blue), when present, extends from the inferior aspect of the anterior clinoid to the middle clinoid (left side of the sellar wall). In cases with a caroticoclinoid ring, the proximal dural ring extends posterior to the carotid artery below the osseous ring and blends into the medial wall of the cavernous sinus (right side of the sellar wall). The middle clinoid base is located at the mid superior level of the sellar prominence directed posteriorly and superiorly to the anterior clinoid at approximately the center of the C shape formed by the carotid prominence. When present, the carotid cave is located between points 4 and 5. The chiasmatic sulcus can be referenced in the sphenoid sinus in the area above the tuberculum recess between both optic prominences. B, Intracranial view showing the anterior, middle and posterior clinoid processes. The distal dural ring is represented with a dark blue line, the proximal dural ring with a yellow line, the dotted lines indicate the locations where the dural rings are seen through the structures represented in the drawing. The dura mater has been removed except for a small piece of the diaphragm. A caroticoclinoid foramen is present on the right side, the proximal dural ring continues posteriorly blending into the periosteal dura below the osseous ring base. The middle clinoid (left side) is intracavernous, note the relationship of the distal and proximal dural rings that fuse posterior to the carotid artery medial to the anterior clinoid tip. The caroticoclinoid ligament (light blue) can be found in some cases as a medial extension of the proximal dural ring and has adhesions to the carotid artery, pituitary and middle clinoid, however, it does not form a different compartment in the cavernous sinus. This ligament may be present in cases without middle clinoid process and its sphenoidal extension is located in the theoretical position of the middle clinoid process in the medial edge of the carotid sulcus. The middle clinoid base is just inferior and lateral to the caroticosellar point and further inferior to the medial opticocarotid point. C, Oblique-anterior view of a sphenoid bone. The anterior wall of the sphenoid sinus has been removed to expose the sellar wall and its recesses on the right side, and the intracranial correspondences on the left side. The bone covering the left optic nerve and parasellar carotid has been removed. The optic strut base corresponds to the lateral opticocarotid recess, which lies anterolateral to the carotid sulcus. This 3-dimensional perspective is partially lost with the endoscopic view that shows the lateral opticocarotid recess as purely lateral to the carotid prominence. The middle clinoid and anterior clinoid processes are represented behind the carotid artery (dotted line). (Images courtesy of AL Rhoton, Jr.)