Magnified endoscopic view of right anterior aspect of cerebellopontine angle. Petrosal and clival bone have been removed to expose the cerebellopontine angle. The facial and vestibulocochlear nerves leave the pontomedullary junction toward the internal auditory meatus and are accompanied by the anterior inferior cerebellar artery. A portion of the posterior inferior cerebellar artery can be seen at the lower border of this image in relation to the glossopharyngeal and vagus nerves. Part of the choroid plexus of the fourth ventricle is visible. The trigeminal nerve (unlabeled) can be seen emerging from the lateral pons. Posterior and inferior to it is the superior petrosal vein, an important venous channel draining the anterior cerebellum and brainstem. It is formed by union of several veins, including the transverse pontine vein, vein of the middle cerebellar peduncle, vein of the cerebellopontine fissure, the pontine trigeminal vein, and anterior lateral marginal vein. The superior petrosal vein empties into the superior petrosal sinus. (Image courtesy of AL Rhoton, Jr.)