Surgical anatomy and neurophysiology of the vagus nerve (VN) for standardised intraoperative neuromonitoring (IONM) of the inferior laryngeal nerve (ILN) during thyroidectomy

Background: Standardisation of the intraoperative neuromonitoring (IONM) technique is a fundamental aspect in monitored thyroid surgery. Vagal nerve (VN) stimulation is essential for problem solving, recognition of any inferior laryngeal nerve (ILN) lesions and prediction of ILN post-operative function. Issues that have been overlooked in the literature, particularly in terms of prospective approaches, are the topographic relationship of the VN with the carotid and jugular vessels as well as the neurophysiology of the VN and ILN that have been studied, with a prospective approach, in patients with various thyroid diseases. Methods: Cooperation with the Human Morphology Department resulted in the completion of a dedicated anatomy report, with the clear objective of providing a detailed anatomic and neurophysiologic description of the VN (n = 263). Results: VN identification and stimulation was feasible in all cases and did not result in increased morbidity or operative time. Most VNs lay on the posterior region of the carotid ship (73%), i.e. the P position in accordance with our model. Mean amplitudes of EMG signals obtained from VN stimulation were 750 ± 279 μV, lower than those obtained with direct INL stimulation (1,086 ± 349 μV). Conclusion: A better understanding of the variability in the VN may be useful not only to minimise complications but also to guarantee an accurate IONM.