Clinical Implication of the Clinoid(C5) Internal Carotid Artery and Dural Rings: A Microsurgical Anatomy

Kim, Jae Min; Bak, Koang Hum; Kim, Choong Hyun; Kim, Nam Kyu

Abstract

To describe the detailed microsurgical anatomy of the clinoid(C5)segment of the internal carotid artery(ICA) and surrounding structures and clarify the anatomical relationships of this region emphasizing their clinical relevance, authors examined in 70 specimens from 35 formalin fixed cadaveric heads. Removal of the anterior clinoid process exposes the C5 segment of the ICA which is encircled by the thin inner dural layer of the cavernous sinus wall. Opening this membrane enables entrance into a narrow space that communicates with cavernous sinus through the proximal dural ring. Unlike the dura of the distal dural ring that is tightly attached to the ICA, the proximal dural ring is always incompetent. The C5 segment of the ICA has been considered by the majority of authors to be extracavernous. This understanding developed because most investigators overlooked the thin inner dural layer encircling the clinoid ICA. The narrow space between the inner dural layer and the ICA communicates with cavernous sinus through an incompetent proximal dural ring. Therefore, the clinoid ICA should be considered to be the most rostral portion of the cavernous (C4)segment of the ICA. The proximal dural ring is a surgical landmark rather than a true dural ring.