Endonasal approach to the posterior skull base. The basilar artery is located in the midline after the paired vertebral arteries merge. The anterior-inferior cerebellar artery (AICA) runs in the petrosal surface of the cerebellum and is related to the abducens nerve. The posterior inferior cerebellar artery (PICA) arises from the vertebral artery and is related to lower cranial nerves. The hypoglossal nerve runs to the hypoglossal canal located in the occipital condyle. The glossopharyngeal nerve, vagus nerve, and oculomotor nerve run to the jugular foramen, which is limited anteriorly by the jugular tubercle. (Image courtesy of JC Fernandez-Miranda)