Unintended Consequences: Vagal Nerve Injury During Continuous Neuromonitoring in Thyroidectomy

To characterize the patterns, mechanisms, and outcomes of vagus nerve (VN) injury associated with continuous intraoperative neuromonitoring (CIONM) during total thyroidectomy and to outline prevention strategies.

A prospectively maintained thyroidectomy database (2014-2024), operative records, anesthesia charts, intraoperative electromyography (EMG) data, and standardized postoperative laryngoscopy.

Retrospective identification of all postoperative VN injuries following total thyroidectomy with CIONM. VN injury was defined as new ipsilateral vocal fold palsy with abrupt or marked VN EMG loss not attributable to recurrent laryngeal nerve (RLN) trauma, confirmed by absent proximal and preserved distal stimulation. Variables included demographics, surgical approach, device type, VN topography, timing and mechanism of injury, EMG pattern, and recovery to 180 days. Incidence was calculated per nerve at risk. Analyses were descriptive.

Among 1060 thyroidectomies (2120 nerves at risk), nine VN injuries occurred (0.42%). Eight were transient and one permanent. Most injuries (89%) arose during initial carotid sheath dissection or probe application, particularly in posterior VN positions or short, thick necks. Older circumferential probes were more often involved. All lesions were segmental with preserved RLN EMG. No global VN damage, macroscopic disruption, thermal injury, or intraoperative hemodynamic instability was observed. Complete EMG loss predicted the only permanent palsy; partial amplitude/latency changes resolved. Early recognition, stopping manipulation, and timely voice therapy supported recovery.

CIONM-related VN injury rate is low (0.4%), and most cases recovered in approximately 4 months. CIONM-related VN injury is usually related to nerve exposure rather than probe handling.