Transclival, paraclival view of vertebrobasilar system and internal carotid arteries. In this image, the middle and upper part of the clivus, including the body of the sphenoid, have been drilled away. The anterior surface of the pons is in view with its overlying basilar artery formed by the union of the right and left vertebral arteries at the pontomedullary junction. A sheet of dura remains intact just deep to the bone. Seen emerging from this junction on right side is the abducens nerve (CNVI). The first branches arising from the basilar artery are the anterior inferior cerebellar arteries. Obscuring the distal end of the basilar artery is the pituitary gland and its infundibulum. The cervical part of the left internal carotid artery (ICA) is in view posteromedial to the infratemporal fossa and the mandibular division of the trigeminal nerve (CNV3) seen emerging from the foramen ovale. The cervical part of ICA continues as the petrous portion within the carotid canal of the petrous temporal bone. It crosses superior to the fibrocartilage filling foramen lacerum (as the short lacerum segment) before entering the middle cranial fossa near the posteroinferior edge of the body of the sphenoid. From here it ascends within the cavernous sinus as the cavernous segment and then makes a 90° degree turn anteriorly at the roof of the cavernous sinus. At the anterior end of the cavernous sinus, the ICA makes another 90° turn superiorly and a final 90° turn posteriorly to pass medial to the anterior clinoid process where it divides into the middle and anterior cerebral branches. The ophthalmic arteries can be seen arising from the ophthalmic segment of ICA. Anterior to the infundibulum is the optic chiasm. Lateral to this are the optic nerves (CNII) that enter the optic canals with the ophthalmic arteries. (Image courtesy of PA Rubino)