14 - New Insights into the Anatomy of the Cervical Vagus Nerve via Gross Dissection and Imaging

Poster Board Number: 14
There are separate poster presentation times for odd and even posters.
Odd poster #s – first hour
Even poster #s – second hour

Co-authors:

Brandon Brunsman - Anatomy - Case Western Reserve University; Jichu Zhang - Biomedical Engineering - Case Western Reserve University; Katharine Workman - Anatomy - Case Western Reserve University; Sara Bokhari - Anatomy - Case Western Reserve University; Noa Nuzov - Biomedical Engineering - Case Western Reserve University; Ari Blitz - Radiology - University Hospitals Cleveland Medical Center and Case Western Reserve University; Michael Markley - Radiology - University Hospitals Cleveland Medical Center and Case Western Reserve University; Daniel Herzka - Radiology - University Hospitals Cleveland Medical Center and Case Western Reserve University; Chris Flask - Radiology - University Hospitals Cleveland Medical Center and Case Western Reserve University; Nicole Pelot - Biomedical Engineering - Duke University; Andrew Shoffstall - Biomedical Engineering - Case Western Reserve University; Andrew Crofton - Anatomy - Case Western Reserve University

Introduction
Invasive cervical vagus nerve stimulation (VNS) is an FDA-approved therapeutic modality for drug-resistant epilepsy and depression. VNS has been hampered by off-target side effects that result from targeting the cervical vagus nerve (VN) as a whole. Ideally, future VNS devices will selectively control an end organ of interest while also targeting fascicles of desired modality (e.g., sensory or motor). Better understanding vagal anatomy at the gross and fascicular levels is necessary first. Our developed dissection technique was combined with multi-resolution imaging modalities including magnetic resonance imaging (MRI) and micro computed tomography (μCT).

Methods
Cadavers (n=14) were 3T MRI scanned prior to dissection to localize the VN. Right and left VNs and their branches were dissected from origin to destination, then painted to facilitate branch classification downstream. Trunks and branches were 3D traced with an optical tracking stylus to measure distances between branches and anatomical landmarks and facilitate co-registration across imaging modalities. The VN was removed, fixed to an acrylic grid, stained with 3% phosphotungstic acid, and scanned with a Scanco Medical μCT 100. Descriptive statistics were calculated for all data. Differences between groups were evaluated via Student’s t-test with ɑ=0.05.

Results
Right and left VN trunks were identified on MRI and followed from the medulla to the carina, but tracing them in full continuity remains elusive. Dissections showed no statistically significant differences in the number of branches of the left vs. right VN or across sex and race. The superior laryngeal nerve, which branches off of the nodose ganglion of the VN, was 31.85 mm (+\- 8.38 mm) inferior to the caudal margin of the jugular foramen. The proximal cervical VN commonly shared an epineural sheath with nearby nerves (hypoglossal nerve, accessory nerve, and sympathetic trunk (ST)). There were 2-6 connections between the VN and the carotid artery, 1-9 between the VN and ST, as well as 1-5 cervical cardiac branches.

Conclusions
The degree of normal anatomical variation of the human VN has not been quantified, but it is vital for visualizing the nerve on imaging. Shared epineurium with nearby nerves complicates tracking the VN in cadavers on MRI. Cervical cardiac branching varies beyond the classical superior and inferior cervical cardiac branches.

Significance
Post-mortem MRI allows visualization of the VN in cadavers and represents a potential method for identifying the VN clinically, which can facilitate improved approaches to VNS therapy. Wide variation in branch patterns indicates that fascicular anatomy must be elucidated across diverse cohorts of subjects to inform future approaches to selective VNS therapy.