A, The insert shows the side of the scalp incision. A frontotemporal craniotomy has been completed and the dura has been elevated from the middle fossa floor and lateral wall of the cavernous sinus. B, Enlarged view. The bony roof over the geniculate ganglion and internal meatus has been removed and the dura lining the meatus opened to expose the facial and superior vestibular nerves. C, Additional middle fossa floor has been removed to expose the petrous carotid, the cochlea in the angle between the greater petrosal nerve and pregeniculate part of the facial nerve, the semicircular canals and tympanic cavity. The tensor tympani muscle and eustachian tube are exposed in front of the petrous carotid artery. D, The bone between the superior and posterior canals has been removed to expose the vestibule with which both ends of the semicircular canals communicate. The vestibule contains the utricle and saccule and communicates below the fundus of the meatus with the cochlea. The meatal segment of the facial nerve courses in the internal acoustic meatus, the labyrinthine segment between the semicircular canals and the cochlea, the tympanic segment between the anterior margin of the lateral canal and the oval window on the medial side of the tympanic cavity, and the mastoid segment descends to exit the stylomastoid foramen. E, The petrous apex, medial to the cochlea and extending under the trigeminal nerve, has been removed to expose the lateral edge of the clivus and the posterior fossa dura. F, The medial tentorial edge has been divided behind the petrous ridge to expose the oculomotor, trochlear, and trigeminal nerves and the basilar artery. (Images courtesy of AL Rhoton, Jr.)