Surgical anatomy of the anterior clinoid process.

We studied the surgical anatomy of the anterior clinoid process (ACP) and its adjacent structures in cadaver heads. We paid special attention to the anatomical relationships between the ACP and adjacent structures to determine the surgical landmarks for safe anterior clinoidectomy. Thirty-five cadaver heads were dissected and the ACP regions were examined in 55 skull sides. We observed that in eight sides the ACP had been pneumatized from the sphenoid sinus. The caroticoclinoid foramen was revealed in only eight sides. The extra-ocular nerves ran forward to the superior orbital fissure at the inferolateral aspect of the ACP, with the oculomotor nerve being closest. The posterolateral area of the carotico-oculomotor membrane was thin and incomplete in nine sides. The study clarified the anatomical relationship between the ACP and its surrounding structures, and identified the major variations experienced. We used these to identify anatomical landmarks to assist the surgeon in the planning of a safe and effective anterior clinoidectomy.