A, The vestibulocochlear nerve enters the internal acoustic meatus with a labyrinthine branch of the AICA. The PICA courses around the glossopharyngeal, vagus, and accessory nerves. The abducens nerve ascends in front of the pons. A subarcuate artery enters the subarcuate fossa superolateral to the porus of the meatus. Choroid plexus protrudes into the cerebellopontine angle behind the glossopharyngeal and vagus nerves. B, The posterior wall of the internal acoustic meatus has been removed. The cleavage plane between the upper bundle, formed by the superior vestibular nerve, and the lower bundle, formed by the inferior vestibular and cochlear nerves, was begun laterally where the nerves have separated near the meatal fundus and extended medially. The nervus intermedius arises on the anterior surface of the vestibulocochlear nerve, has a free segment in the cistern and/or meatus, and joins the facial nerve distally. The facial nerve is located anterior to the superior vestibular nerve and the cochlear nerve is anterior to the inferior vestibular nerve. C, The cleavage plane between the cochlear and inferior vestibular nerves, which is well developed in the lateral end of the internal acoustic meatus, has been extended medially. Within the cerebellopontine angle, the superior vestibular nerve is posterior and superior, the facial nerve anterior and superior, the inferior vestibular nerve posterior and inferior, and the cochlear nerve anterior and inferior. D, The superior and inferior vestibular nerves have been divided to expose the facial and cochlear nerves. A labyrinthine branch of the PICA enters the internal meatus. (Images courtesy of AL Rhoton, Jr.)