Fig. 5 Anatomic relationships of facial nerve trunk and brain stem structure. Anterior view of ventral aspect of brain stem and clivus, especially cerebellopontine angle. The cerebral hemispheres were removed and the oculomotor and trigeminal nerves were divided to provide this view of the anterior surface of the brain stem. A. The superior cerebellar arteries (SCA) and posterior cerebral arteries (PCA) arise from the superior end of the basilar artery (BA). The oculomotor (III) and trochlear (IV) nerves are above and the trigeminal (V) nerves are below the superior cerebellar arteries. The right anterior inferior cerebellar artery (AICA) arises from the basilar artery, courses below the abducens nerve (VI), and passes between the nervus intermedius (VII NI) and the facial motor root (VII) anteriorly and the vestibulocochlear nerve (VIII) posteriorly. The left AICA is a duplicate artery. The rostral duplicate AICA (Dup. Ro. AICA) is not nerve related, but the caudal AICA (Dup. Ca. AICA) is nerve related and passes between the facial and vestibulocochlear nerves. The left posteroinferior cerebellar artery (PICA) arises from the left vertebral artery (VA). The hypoglossal (XII), glossopharyngeal (IX), vagus (X), and spinal accessory (XI) nerves are lateral to the vertebral arteries. The carotid arteries (CA) and the pituitary stalk (Stalk) have been divided. The premeatal segments (Pre. Mea. Seg.) approach the nerves, the meatal segments (Mea. Seg.) pass between the nerves, and the postmeatal segments (Post. Mea. Seg.) pass above the flocculus. A recurrent perforating artery (RPA) and an internal auditory artery (IAA) arise from the right AICA. B. Enlarged anterosuperior view of the right cerebellopontine angle. The premeatal segment passes below the abducens nerve, the meatal segment passes between the eighth cranial nerve and the nervus intermedius, and the postmeatal segment passes above the flocculus. A recurrent perforating artery and an internal auditory artery arise from the meatal segment. Pontine arteries arise from the right side of the basilar artery. (Martin RG, Grant JL, Peace D: Microsurgical relationship of the anterior inferior cerebellar artery and the facial-vestibulocochlear nerve complex. Neurosurgery 6:483, 1980)