Ventral view of the cerebellopontine angle. The posterior inferior cerebellar artery (PICA) is the largest branch of the intradural vertebral artery and has several named segments: the anterior medullary segment, the lateral medullary segment, and the tonsillomedullary segment prior to coursing around the cerebellar tonsils. The telovelotonsillar and cortical segments of PICA are not visible in this ventral view. The tonsillomedullary segment courses inferiorly adjacent to the glossopharyngeal, vagus and accessory spinal nerve fibers. The anterior inferior cerebellar artery (AICA) arises from the basilar artery and, during its anterior pontine segment, lies just rostral to the abducens nerve. The lateral pontine segment of AICA has a close relationship with the cranial nerve VII-VIII complex before the AICA courses between the flocculus and the middle cerebellar peduncle. (Image courtesy of AL Rhoton, Jr.)