A, The facial nerve has been transposed and the cochlea and petrous apex removed to complete the transcochlear exposure of the anterior aspect of the brainstem and the basilar artery. B, Enlarged view of the retrosigmoid exposure to compare with the exposure obtained with the various modification of the presigmoid approach. C, In the retrosigmoid exposure the vestibulocochlear nerve has been elevated and the glossopharyngeal nerve depressed to expose the basilar artery at the origin of the AICA. D, Subtemporal exposure. The temporal lobe has been elevated to expose the optic tract and oculomotor nerve and the PCA, internal carotid, and anterior choroidal arteries. E, The tentorium has been opened while preserving the trochlear nerve. The SCA courses below and the PCA above the oculomotor and trochlear nerves. F, Minimal mastoidectomy modification of the presigmoid approach. The minimal mastoidectomy approach is completed by removing only enough bone in the front of the sigmoid sinus so that the presigmoid dura can be opened to expose the posterior cranial fossa. The bony capsule of the labyrinth is not exposed in the minimal mastoidectomy as it is in the retrolabyrinthine approach. The exposure shown with the minimal mastoidectomy in this figure is to be compared with the retrosigmoid exposure shown in B. (Images courtesy of AL Rhoton, Jr.)