32 - Characterizing Fascicular Anatomy of the Human Accessory Nerve Including Connections with the Glossopharyngeal, Vagus, and Hypoglossal Nerves

Poster Board Number: 32
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Co-authors:

Jessi Villafuerte - Anatomy - Case Western Reserve School of Medicine; Steven O'Neill - Anatomy - Case Western Reserve University School of Medicine; Leina Lunasco - Case Western Reserve University School of Medicine; Brandon Brunsman - Anatomy - Case Western Reserve University School of Medicine; Jichu Zhang - Biomedical Engineering - Case Western Reserve University School of Engineering; Justin Chin - Biomedical Engineering - Case Western Reserve University School of Engineering; Anandakumar Shunmugavel - Biomedical Engineering - Case Western Reserve University School of Engineering; Zeyna Samba - Anatomy - Case Western Reserve University School of Medicine; Katharine Workman - Anatomy - Case Western Reserve University School of Medicine; Sara Bokhari - Anatomy - Case Western Reserve University School of Medicine; Aniruddha Upadhye - Biomedical Engineering - Case Western Reserve University School of Engineering; Noa Nuzov - Biomedical Engineering - Case Western Reserve University School of Engineering; Nicole Pelot - Biomedical Engineering - Duke University School of Engineering; Andrew Shoffstall - Biomedical Engineering - Case Western Reserve University School of Engineering; Andrew Crofton - Anatomy - Case Western Reserve University School of Medicine

Abstract Body :
Introduction:The accessory nerve (CN XI) consists of both cervical and cranial rootlets that coalesce shortly after leaving the spinal cord and medulla. Surgical interventions of the skull base and jugular foramen, such as brainstem aneurysm clipping or tumor resections, can involve the cervical and cranial elements of CN Xl. Classically, CN XI was thought to only carry motor fibers, but more recent studies suggest that it also carries sensory fibers. We seek to characterize the fascicular anatomy of CN XI via microcomputed tomography (microCT), including tracking cross connections with the glossopharyngeal (CN IX), vagus (CN X), and hypoglossal (CN XII) nerves, to better understand the structure and function of CN XI. Methods: Cranial nerves IX through XII were dissected on the right side in an embalmed African-American male cadaver, 77 years of age at time of death. After removal, the nerves were stained with 3% phosphotungstic acid for 48 hours and imaged with a Scanco Medical μCT 100 scanner (11.4 μm isotropic voxels). Nerve fascicles were segmented on the microCT images from the inferior margin of the jugular foramen (IJF) to approximately 49 mm distal. Results:The CN XI fascicles split 10 times with the proximal-most splitting event occurring 4 mm below the IJF and the distal splitting event occurring 27 mm below the IJF. There were 9 fascicular merging events with the proximal-most event occurring 5 mm below the IJF and the distal-most at 39 mm below the IJF. Splitting and merging events sometimes remained local within CN XI but in other instances, after splitting, CN XI fascicles merged with fascicles of the vagus or hypoglossal. There were also CN XI fibers that merged with a branch of the vagus nerve that traveled distally to the intercarotid plexus. No CN XI fibers merged with the glossopharyngeal nerve. Conclusions:Our findings reveal that the fascicles of the rostral CN XI split or merge every ~0.5 mm on average. Further, we observed communicating branches between CN XI and the vagus and hypoglossal nerves. Significance/Implications: Our study adds insights into the complexity of CN XI that have heretofore been unappreciated. Further research is needed to better understand the significance of the splitting and merging events in addition to identifying the fiber types and their targets. Complexity across and within individuals also needs to be explored to improve our understanding of the variability within this cranial nerve.