Left lateral view of brainstem and cerebellopontine angle. The basilar artery is visible on the left side of the image coursing on the anterior midline of the pons. It is formed by union of the right and left vertebral arteries and gives rise to anterior inferior cerebellar, pontine, superior cerebellar, and terminal posterior cerebral arteries. The oculomotor nerve emerges from the midbrain within the interpeduncular fossa and passes forward between the superior cerebellar and posterior cerebral arteries. Just lateral to the posterior clinoid process it pierces the dura covering the roof of the cavernous sinus. The trochlear nerve originates from the dorsal surface of the midbrain near the midline cerebral aqueduct and wraps around the cerebral peduncles within the subarachnoid space and pierces dura slightly inferolateral to the oculomotor nerve. The trigeminal nerve leaves the anterolateral surface of the pons. The abducens nerve emerges from the pons at the pontomedullary junction anteriorly. The facial and vestibulocochlear nerves leave the brainstem at the cerebellopontine angle and enter the internal auditory canal. The glossopharyngeal, vagus, and spinal accessory nerves leave the upper lateral medulla and course toward the jugular foramen. The foramen of Luschka (lateral foramen of fourth ventricle) is located just posterior to the root of the glossopharyngeal nerve and is the lateral opening of the fourth ventricle, which is bounded by the pons, medulla, and cerebellum. A portion of choroid plexus protrudes from the foramen. (Image courtesy of PA Rubino)