Paraclinoid Aneurysms: Part I—Superior (True Ophthalmic) Aneurysms

This article is the first of three parts. Several aneurysm classification schemes have been proposed for aneurysms arising from the proximal segment of the internal carotid artery in the vicinity of the anterior clinoid process. We have found these schemes to be either contradicting or overlapping. Our desire to categorize these aneurysms more accurately has been aided by an evolving insight into their intricate anatomy as they relate to the complex region of the skull base. We seek to make possible a more accurate definition of the location of the aneurysm preoperatively, thereby allowing for more accurate selection of the proper treatment modality, as well as the best surgical approach and surgical steps, consequently increasing the safety of the treatment. This article presents a classification system we propose based on our experiences with proximal internal carotid artery aneurysms arising in proximity to the anterior clinoid process. Our system is based on analysis of surgical and anatomic findings, correlation of these findings with the radiologic features, and comparison of these findings with previously reported classifications. We emphasize the unique features of each aneurysm type as we present the surgical techniques required for intraoperative understanding as well as successful and safe clipping of each type. This classification system encompasses aneurysms classified by previous methods.