The advantage of the combined use of intraoperative neuromonitoring and percutaneous ultrasonography of the larynx as a screening for postoperative vocal cord paresis
Authors: Baychorov E. Kh. , Kazeev D. A. , Uzdenov N. A. 
Published: December 2022

Background. One of the most common complications during thyroid surgery after hypoparathyroidism is a violation of the mobility of the vocal folds - paresis or paralysis of the larynx. The incidence of damage to the recurrent laryngeal nerves during primary surgical interventions can vary from 1 to 30%. Intraoperative neuromonitoring is the most effective method to reduce the amount of damage to the laryngeal nerves during surgical interventions on the thyroid and parathyroid glands. Assessment of the state of the vocal cords in the preoperative and postoperative period is crucial. In the preoperative period, this helps establish baseline characteristics and identify pre-existing laryngeal paresis, while postoperative early identification of vocal cord paresis helps develop a rapid treatment plan. Indirect laryngoscopy is still considered the reference standard for vocal cord examination. The main advantage is the ability to visualize the vocal cords in 99% of cases. However, this is an invasive procedure that can be painful and uncomfortable for patients, and increases medical costs and lead time.

Materials and methods. The results of intraoperative neuromonitoring were analyzed in 25 patients who underwent total thyroidectomy according to indications (diffuse nodular non-toxic goiter — 17 patients (68%), diffuse nodular toxic goiter — 4 patients (16%), autoimmune thyroiditis, diffuse — nodular form — 4 patients (16%)), from September 2021 to February 2022. The patients’ age ranged from 18 to 73 years. There were 23 women (92%), men — 2 (8%). In the study, a C2 neuromonitor (InoMed, Germany), an electrode for EMG recording on an endotracheal tube, and a bipolar forked stimulating probe were used. To assess the mobility of the vocal folds, all patients underwent percutaneous ultrasonography before and after thyroid surgery.

Results and discussion. In 20 patients (80%) before surgery on transcutaneous ultrasound of the larynx, the visualization of the structures of the larynx was good (grade 4-5), in 2 male patients (8%), the visualization of the structures of the larynx was satisfactory (grade 3), in 3 women (older than 45 years (12%)) — visualization of the structures of the larynx was satisfactory (grade 3), in all 25 patients (100%) — complete or normal symmetrical movement of the vocal folds (grade I). During the performance of precision extrafascial thyroidectomy in 3 patients (12%), a decrease in the amplitude of oscillations was recorded during stimulation of the left recurrent laryngeal nerve and the left vagus nerve, in order to prevent bilateral paresis of the larynx, it was decided to confine ourselves to hemithyroidectomy followed by a staged right-sided hemithyroidectomy. A day after the performed left-sided hemithyroidectomy, percutaneous ultrasound of the larynx in 2 patients showed a violation of the mobility of the vocal fold on the left (grade II), in 1 patient — symmetrical movement of the vocal folds (grade I) — a false positive reaction. In 22 patients (88%) who underwent total thyroidectomy on percutaneous ultrasound of the larynx, complete or normal symmetrical movement of the vocal folds (I degree).

Conclusion. Intraoperative neuromonitoring is an effective tool to localize the recurrent laryngeal nerves regardless of whether a loss of signal (LOS) has occurred, as well as to determine the type of LOS (LOS 1, LOS 2) and staged thyroidectomy in the presence of LOS. Percutaneous vocal cord ultrasonography is currently an effective screening tool, saving 80% of patients from unnecessary invasive laryngoscopy. The complex of these methods should be an obligatory component in surgical interventions on the thyroid and parathyroid glands.