Cisternal segments of the glossopharyngeal, vagus, and accessory nerves: detailed magnetic resonance imaging–demonstrated anatomy and neurovascular relationships

Abstract

The aim of this study was to determine whether high-resolution MR imaging is suitable for identifying and differentiating among the nerve root bundles of the glossopharyngeal (cranial nerve [CN] IX), vagus (CN X), and accessory nerves (CN XI) as well as any adjacent vessels. Twenty-five patients (50 sides) underwent MR imaging using the 3D constructive interference in steady-state (CISS) sequence, as well as noncontrast and contrast-enhanced 3D time-of-flight (TOF) MR angiography. Two individuals scored these studies by consensus to determine how well these sequences displayed the neurovascular contacts and nerve root bundles of CNs IX and X and the cranial and spinal roots of CN XI. Landmarks useful for identifying each lower CN were specifically sought. The 3D CISS sequence successfully depicted CNs IX and X in 100% of the sides. Nerve root bundles of the cranial segment of CN XI were identified in 88% of the sides and those of the spinal segment of CN XI were noted in 93% of the sides. Landmarks useful in identifying the lower CNs included the vagal trigone, the choroid plexus of the lateral recess, the glossopharyngeal and vagal meatus, the inferior petrosal sinus, and the vertebral artery. The combined use of 3D CISS and 3D TOF sequences demonstrated neurovascular contacts at the nerve root entry or exit zones in 19% of all nerves visualized. The combined use of 3D CISS MR imaging and 3D TOF MR angiography (with or without contrast) successfully displays the detailed anatomy of the lower CNs and adjacent structures in vivo. These imaging sequences have the potential to aid the preoperative diagnosis of and the presurgical planning for pathology in this anatomical area.