Use of a single bipolar electrode in the posterior arytenoids muscles for bilateral monitoring of the recurrent laryngeal nerves in thyroid surgery: standardization of the technique

Abstract

Sir, Dr. Haerle and associates [1] reported a series in which they described a new technique for intraoperative neuromonitoring (IONM) with a single bipolar electrode placed in the posterior arytenoids muscles. In the last 10 years major improvements, new and safe technologies have been proposed and applied in thyroid surgery. For example, IONM to prevent laryngeal nerve paralysis [2], the perioperative measurement of iPTH to avert symptomatic hypocalcemia [3], new devices for hemostasis and dissection to better control bleeding [4]; furthermore the introduction of genetic screening with improvement of survival rate [5] and the improvement of perioperative life quality by minimally invasive procedures [6]. Thus, the impact of these modern technologies on quality of thyroid surgery is remarkable [7]. Technical advances currently allow accurate, invasive or noninvasive RLN monitoring during thyroidectomy [2]. RLN monitoring during thyroidectomy has diVerent speciWc functions: Wrst to facilitate initial neural identiWcation and to aid in conWdent neural dissection. Perhaps, RLN monitoring’s main function is that of intraoperative prediction of postoperative function. Blunt and stretch injury to the nerves may not always be visibly detectable [8, 9]. Bergenfelz [10] reported that in only one of ten cases of RLN injury were surgeons aware of the injury. There is a technical issue that I would like to comment. The standardization of IONM technique covers a fundamental technical aspect in thyroid and parathyroid surgery. Dr. Haerle stimulated the RLN distally at its crossing with the inferior thyroid artery in this series of patients. Timmermann [11] have Wrst proposed stimulation of the vagus nerve at the beginning and at the end of operation. Ulmer presented a technique of real-time continuous RLN monitoring by stimulation of the vagal nerve based on a new vagal nerve cuV electrode [12]. According to Dralle [2], vagal stimulation is in fact essential to recognize any RLN lesions and to predict nerve postoperative function. In fact, in neurogenic lesions of the RLN distal stimulation near the larynx produces a false negative, “normal” IONM signal [2]. Only vagal stimulation and, in addition, electromyographic registration of signals, which easily uncovers all kinds of artifacts, can help avoid spurious Wndings during thyroidectomy with IONM [2]. Finally, electrical identiWcation of the RLN reinforces but does not substitute for its visual identiWcation, and provides the surgeon with a new functional dimension of surgical anatomy. As evolving and expanding rapidly, a new technology such as IONM should be carefully assessed in each application to deWne its exact role and to clarify its limitations for improvement of our patient care. Certainly, cases that can be recognized preoperatively as likely having greater risk to the RLN should be monitored. These cases include: cases of malignancy, thyroid surgery accompanied by signiWcant lymph node resection, surgery for Graves’ disease and thyroiditis, surgery for substernal goiter, revision surgery, and surgery after external beam radiotherapy.