Posterosuperior view of the right cerebellopontine angle. The cerebellum has been reflected and bone removed from the petrous portion of temporal at the internal acoustic meatus. The facial (CN VII) and vestibulocochlear (CN VIII) nerves can be seen entering the internal acoustic meatus and the glossopharyngeal (CN IX), vagus (CN X), and spinal accessory (CN XI) nerves can be seen entering the jugular foramen. The vertebral artery gives rise to the posterior inferior cerebellar artery (PICA) that often passes between vagus (CN X) and spinal accessory (CN XI) nerves before they enter the jugular foramen. The vertebral arteries unite to form the basilar artery. Its anterior inferior cerebellar artery (AICA) passes between CN VII and VIII. It usually gives off the labyrinthine artery that travels with CN VIII to supply the inner ear. The superior petrosal vein (vein of Dandy) is an important venous drainage system in the posterior fossa. It drains the anterior cerebellum and brainstem and usually forms by union of the vein of the cerebellopontine fissure, the pontine trigeminal vein, and the vein of the middle cerebellar peduncle. The superior petrosal vein empties into the superior petrosal sinus. (Image courtesy of AL Rhoton, Jr.)