Fig. 11. View of the left brain stem showing vessel causing cross-compression of the anterior caudal aspect of the root exit zone of the facial nerve. vert. = vertebral artery; pica = posterior inferior cerebellar artery. (Jannetta PJ: Hemifacial spasm. In Samii M, Jannetta PJ (eds): The Cranial Nerves, p 486. New York, Springer-Verlag, 1981)