Left posterolateral view of a pre-sigmoid approach to the posterior fossa after partial resection of the petromastoid temporal bone. The tentorium has been incised and retracted along with the temporal lobe and the vein of Labbe, which enters the transverse-sigmoid junction just medial and superior to the image. This approach allows visualization of the cerebellopontine angle with the facial and vestibulocochlear nerves as they enter the internal auditory canal. Visualized superior to this complex is the trochlear nerve, and inferiorly the glossopharyngeal and vagus nerves. (Image courtesy of AL Rhoton, Jr.)