Surgical Landmarks for the Internal Carotid Artery in Endoscopic Endonasal Approaches. S and T, 0-degree view in another specimen. The part of the clivus where the roof of the fossa of Rosenmüller and the Eustachian tube attaches had been drilled. The thick, nonexpansile fibrocartilaginous attachment of both structures is a continuation of the basopharyngeal fascia and is continuous with the fibrous tissue overlying the foramen lacerum. The configuration of the paraclival ICA with respect to this fibrocartilaginous tissue covering the foramen lacerum is similar to that of a foot in a sock; hence, we termed that tissue the ICA sock. The ICA sock is an important landmark for identifying the proximal part of the paraclival ICA especially in sinuses that are poorly pneumatized and in cases in which the vessel is displaced by an offending lesion. U and V, Landmarks for the paraclinoid ICA. U, 0-degree view in the sphenoid sinus after the completion of bilateral anterior and posterior ethmoidectomies and sphenoidotomies. The lateral opticocarotid recess (LOCR) is a triangular osseous depression and represents the ventral surface of the optic strut as seen endoscopically through the sphenoid sinus. Superior to the LOCR is the floor of the optic canal, inferior to it is the superior orbital fissure, and medial to it is the bone overlying the lateral portion of the paraclinoid ICA. At the lateral most edge of the tuberculum sellae and medial to the paraclinoid ICA is an osseous depression, the lateral tubercular recess (LTR). The distal osseous arch (DOA) of the carotid sulcus is a convex osseous arch (asterisks) that connects the LTR to the medial aspect of the LOCR. The medial opticocarotid recess (MOCR) (black curve) is the teardrop-shaped area formed at the medial junction of the paraclinoid ICA canal and the optic canal. The lateral vertex of the teardrop is based at the medial aspect of the LOCR where the paraclinoid ICA intersects with the optic nerve. The medioinferior vertex is situated at the junction of the DOA with the inferior aspect of the LTR and the superolateral aspect of the face of the sella. The mediosuperior vertex is at the site of the point where a vertical line from the medioinferior vertex transects the medial projection of the floor of the optic canal. The LOCR, MOCR, LTR, and DOA represent the osseous framework guarding access to the paraclinoid ICA. V, 0-degree view. The bone overlying the osseous structures described was removed and the dura exposed. The dura lining the DOA of the carotid sulcus forms the anterior segment of the distal dural ring, which extends medially to the LTR. The dura of the MOCR (black curve in U) is in continuation with the distal dural ring, the tubercular dura, and the periosteal dura lining the medial edge of the paraclinoid ICA. The interfalciform ligament represents the medial extension of the falciform ligaments bilaterally. It is a distinct band of dural thickening that lines the chiasmatic sulcus and hence separates the tubercular dura caudally from the dura of the planum sphenoidale rostrally. (Images courtesy of AL Rhoton, Jr.)