The anatomical integrity of the recurrent laryngeal nerve (RLN) is generally preserved by visual identification, and its exposure is mandatory during thyroid surgery. Intraoperative nerve monitoring (IONM) is used as an adjunct to visual identification to confirm the motor activity of both the RLN and the external branch of the superior laryngeal nerve (EBSLN).
We performed total thyroidectomy for the treatment of hyperthyroidism using IONM for both these nerves. The procedure was started from the dominant left lobe. Pre-dissection stimulation (V1) of the left vagus nerve showed normal function of the intrinsic laryngeal muscles. We could not visually, but could functionally, identify the left EBSLN by IONM. EBSLN stimulation generating cricothyroid muscle (CTM) contraction also induced vocal cord action recorded by nerve monitoring. We identified an extralaryngeal terminal bifurcation of the left RLN. Analysis of sound signal and wave amplitude after pre-dissection (R1) stimulation showed normal motor activity on the anterior branch and sensory function on the posterior branch. Stimulation of the left RLN also induced CTM twitches. At the end of the surgery, post-dissection (R2) and (V2) stimulations confirmed proper motor function of the RLN. EBSLN stimulation generated cricothyroid muscle (CTM) contraction revealing the normal function of this branch. The right lobe was also dissected under the guidance of IONM. All stages of monitoring were the same as on the left side, which showed proper function of the nerves at the end of the surgery.
IONM contributes to the identification of the EBSLN and establishes its proper motor function by observation of CTM contraction. It assesses the function of the RLN at the beginning, during, and the end of the surgery, with vocal cord mobility being received by surface electrodes creating a sound signal while recording the waveform amplitude. Based on recordable amplitudes after stimulation of EBSLN and induction of CTM twitches by stimulation of the left RLN, IONM establishes real-time motor interconnections between EBSLN and RLN via laryngeal anastomosis.
Thyroid surgery RLN EBSLN IONM
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