A, The insert shows the site of the craniotomy. The frontal and temporal lobes have been retracted to expose the optic and oculomotor nerves and the anterior and middle cerebral and posterior communicating arteries. B, The opticocarotid triangle, located between the optic nerve and the carotid and anterior cerebral arteries, has been opened with gentle retraction to expose the basilar apex and the ipsilateral oculo-motor nerve passing forward between the PCA and SCA. C, The exposure has been directed medially above the optic chiasm to expose the region of the anterior communicating artery. D, The frontal lobe has been elevated to expose the contralateral carotid and anterior and middle cerebral arteries. E, The carotid artery has been elevated to expose the basilar artery apex through the interval between the carotid artery and oculomotor nerve. The posterior clinoid process blocks access to the basilar artery. F, The anterior clinoid process and the roof of the cavernous sinus have been removed to provide access to the posterior clinoid process. The upper dural ring is located at the level of the upper margin of the anterior clinoid process. (Images courtesy of AL Rhoton, Jr.)