Fascicular Organisation and Neuroanatomy of the Porcine and Human Vagus Nerves: Allowing for Spatially Selective Vagus Nerve Stimulation

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Vagus nerve stimulation (VNS) often results in off‐target effects due to the unknown fascicular organisation of the cervical vagus nerve and thus nonspecific nature of stimulation. This currently limits its therapeutic efficacy in treating epilepsy and depression and restricts its extension to treating numerous other conditions, such as heart failure and lung injury, for which it could be a promising treatment. The purpose of this work was to determine the fascicular anatomical representation of the recurrent laryngeal, cardiac and pulmonary branches of the vagus nerve at the mid‐cervical level of VNS cuff placement in the vagus nerve in pigs using micro‐computed tomography (microCT) to trace anatomical connections to end‐organs with the intention of extension to humans.The left vagus nerves were dissected from mid‐cervical level to the branches of the lungs, heart and larynx in four domestic female 60‐70 kg pigs. Nerves were fixed, sectioned into 4 cm lengths with registration landmarks, soaked in Lugol’s solution (1% total iodine) for five days for sufficient contrast staining and microCT‐scanned (Nikon XT H 225, Nikon Metrology) with a molybdenum target and 7 µm voxel size, 35 kVp energy, 114 mA current, 4 W power, 0.25 fps in 4 s exposure time, and 3176 projections. Subsequently, scans were reconstructed in CT Pro 3D (Nikon Metrology) and analysed in ImageJ. Fascicles of the three target organs/fascicle groups were segmented and traced with Neurolucida 360 (MBF Bioscience) from the point the organ‐specific branch enters the vagus nerve to mid‐cervical level (20‐25 cm total length per nerve).The three identified fascicular groups remained discrete at the cervical level (26%, 23% and 4% of total vagus nerve area for pulmonary, recurrent laryngeal and cardiac fascicle groups, respectively, with significant separation of centres of mass (P<0.05)). These three distinct regions contained overlap only between a small number of pulmonary and recurrent laryngeal fascicles (<11%). The cardiac fascicles remained separate. This confirms organotopic organisation of the cervical vagus nerve according to organ/function for cardiac, pulmonary and recurrent laryngeal fascicles. Work is in progress to delineate similar fascicular organisation in excised cadaveric human vagus nerves. Knowledge of the fascicular organisation of the vagus nerve will enable accurate spatially selective VNS which may allow for avoidance of off‐target effects and so improve its therapeutic efficacy.