Object: The authors report on the surgical anatomy of the juxta-dural ring area of the internal carotid artery to add to the information available about this important structure.
Methods: Twenty sides of cadaver specimens were used in this study. The plane of the dural ring was found to incline in the posteromedial direction. Medial inclination was measured at 21.8 degrees on average against the horizontal line in the anteroposterior view on radiographic studies. Posterior inclination was measured at 20.3 degrees against the planum sphenoidale in the lateral projection, and the medial edge of the dural ring was located 0.4 mm above the tuberculum sellae in the same projection. The lateral edge of the dural ring was located 1.4 mm below the superior border of the anterior clinoid process. The carotid cave was situated at the medial or posteromedial aspect of the dural ring; however, two of the 20 specimens showed no cave formation. The carotid cave contained the subarachnoid space in 13 sides, the arachnoid membrane only in three sides, and the extraarachnoid space in two sides. The authors propose that the marker of the medial side of the dural ring, which is more proximal than the lateral, is the tuberculum sellae in the lateral view on radiographic studies. In the medial aspect of the dural ring the intradural space can be situated below the level of the tuberculum sellae because of the existence of the carotid cave.
Conclusions: An aneurysm arising from the medial side of the juxta-dural ring area even below the tuberculum sellae is a potential cause of subarachnoid hemorrhage.