Endoscopic endonasal inferior transclival approach, step-by-step dissection. The inferior clivus, anterior margin of the foramen magnum, superior tubercle of C1, and odontoid tip have been drilled away. The anterior arch of C1 has been preserved. The clivectomy has extended laterally to include the medial aspect of the occipital condyles. The key landmark when drilling the condyle is the cortical bone of the most medial aspect of the ventral surface of the hypoglossal canal. The jugular tubercle is located above the hypoglossal canal. Note the spatial correlation between the supracondylar groove and the hypoglossal canal. (Image courtesy of JC Fernandez-Miranda)