Detailed MR imaging anatomy of the cisternal segments of the glossopharyngeal, vagus, and spinal accessory nerves in the posterior fossa: the use of 3D balanced fast-field echo MR imaging.

BACKGROUND AND PURPOSE The cisternal segments of the lower cranial nerves (CNs) adjacent to the jugular foramen (JF) are difficult to identify reliably by routine MR imaging. We performed a 3D balanced fast-field echo imaging technique (3D-bFFE) to obtain detailed anatomy of the cisternal segments of CNs IX, X, and XI. MATERIALS AND METHODS 3D-bFFE was used to image the cisternal segments of the lower CNs in 20 healthy volunteers. As an anatomic landmark, CSF recesses adjacent to the JF were divided into 3 parts: the recess for the cochlear aqueduct, the recess for CN IX, and the recess for the CN X/XI complex. MR images were evaluated to identify the cisternal segment of each cranial nerve in relation to these anatomic landmarks. RESULTS The mean angles of the recess for the cochlear aqueduct for CN IX and CN X/XI to the posterior petrous bone were 41.6 +/- 2.5 degrees , 69.7 +/- 3.1 degrees , and 76.0 +/- 3.4 degrees , respectively (P < .01). The mean length of the recess for the cochlear aqueduct for CN IX and the CN X/XI complex was 5.91 +/- 0.19, 5.08 +/- 0.11, and 4.76 +/- 0.13 cm, respectively (P < .01). 3D-bFFE adequately depicted the cisternal segments of CN IX on 38 sides (95%) and the CN X/XI complex on 39 sides (97.5%). CONCLUSIONS The cisternal segments of CN IX, CN X, and CN XI are well identified by using 3D-bFFE, especially by determining the angles of the CSF recesses adjacent to the JF.