Neurovasculature relationships on anterior brainstem. The vertebral arteries ascend to the pontomedullary junction and join to form the basilar artery that courses on the basilar pons. At this junction it gives rise to the anterior inferior cerebellar artery (AICA) in proximity to the abducens nerve.  The AICA continues laterally into the cerebellopontine angle in relation to the facial and vestibulocochlear nerves where it gives rise to the labyrinthine artery to the inner ear. Near the pontomesencephalic junction the basilar artery gives rise to the superior cerebellar arteries before terminating as the posterior cerebral arteries (PCA) in the interpeduncular cistern. The oculomotor nerves emerge from the midbrain and pass between these two arteries. The initial P1 segment of the PCA receives the posterior communicating artery from the internal carotid artery before continuing as the P2 segment coursing posteriorly around the cerebral peduncles. Superior to the midbrain can be seen a small piece of the diencephalon, containing the mammillary bodies and tuber cinerium of the hypothalamus. These are in close relationship with the optic nerves, chiasm, and tracts. The trigeminal nerves emerge from the anterolateral surface of the pons. The glossopharyngeal and vagus nerve roots emerge from the postolivary sulci. The posterior inferior cerebellar arteries arise from the vertebral arteries near the olive of the medulla while the anterior spinal arteries join to form a single vessel that descends in the anterior medial fissure of the spinal cord. (Image courtesy of AL Rhoton, Jr.)