Extradural approach to the upper clivus. The dura of the anterior wall of the cavernous sinus is being displaced to facilitate identification of the tip of the posterior clinoid. This maneuver often causes tearing of the single-layered anterior wall of the cavernous sinus and venous bleeding. The top of the posterior clinoid is typically firmly adhered to the dura, as it serves as attachment for the interclinoidal and posterior petroclinoidal ligaments. (Image courtesy of JC Fernandez-Miranda)