Innervation of the human posterior cricoarytenoid muscle by the external branch of the superior laryngeal nerve

Background The posterior cricoarytenoid muscle is the abductor muscle for the vocal cords and is innerved by the recurrent laryngeal nerve (RLN). The purpose of this study was to present our determination if the external branch of the superior laryngeal nerve (SLN) contributes to the motor innervation of the posterior cricoarytenoid muscle. Methods We performed electromyographies (EMGs) via needle electrodes on 47 posterior cricoarytenoid muscles from 28 patients during thyroidectomy (9 lobectomies and 19 total thyroidectomies) with intraoperative neural monitoring. The RLN, vagus nerve, and external branch of the SLN were stimulated intraoperatively and the responses were evaluated by EMG. Results Positive EMG responses were obtained from 16 (34%) of 47 posterior cricoarytenoid muscles after external branch of the SLN stimulation. The EMG of the posterior cricoarytenoid muscle was unilaterally positive in 8 of 19 patients (42%) with total thyroidectomy, and 2 of 19 patients (10.5%) were bilaterally positive. Conclusion The external branch of the SLN contributes to the ipsilateral posterior cricoarytenoid muscle innervation in one-third of the cases. This contribution is usually unilateral, but is occasionally bilateral.