Magnetic resonance imaging of cranial nerves IX, X, XI, and XII.

Cranial nerves IX (glossopharyngeal), X (vagus), and XI (spinal accessory) are intimately related. Therefore, for imaging purposes they are best considered as a unit rather than as individual structures. The XIth nerves are not considered true cranial nerves because they are formed by cephalic (bulbar) and caudal (spinal) divisions. The XIIth (hypoglossal) nerves arise inferiorly to the above mentioned cranial nerves and exit the skull via a different set of foramina. Because the course of these four pairs of cranial nerves extends from the base of the skull to the upper thorax, a combination of both magnetic resonance imaging (MRI) and computed tomography is needed for optimal evaluation. This article will emphasize the use of MRI when appropriate.