Transoral Endoscopic Thyroidectomy with Standardized Neural Monitoring

Injuries to the recurrent inferior laryngeal nerve remain one of the major postoperative complications after thyroid and parathyroid surgery. Damage to this nerve can result in a temporary or permanent palsy, which is associated with vocal cord paresis or paralysis. Recent clinical practice guidelines of the American Academy of Otolaryngology-Head and Neck Surgery and American Thyroid Association guidelines recommend that all patients have a preoperative voice assessment. Visual identification of the recurrent laryngeal nerve is a common procedure to prevent nerve injury during thyroid and parathyroid surgery. Recently, intraoperative neuromonitoring has been introduced to facilitate the localization of the nerves and to prevent their injury during surgery. Intraoperative neuromonitoring allows nerve identification using an electrode, where, to measure the nerve response, the electric field is converted to an acoustic signal. The main clinically significant intraoperative neuromonitoring applications thus far include (1) neural electrical mapping of the recurrent laryngeal nerve before visual identification at surgery; (2) identification of anatomical variants of normal recurrent laryngeal nerve anatomy that have increased potential for injury, such as extralaryngeal bifurcation of the recurrent laryngeal nerve with the anterior branch typically motor in function and the posterior branch typically sensory in function; (3) nerve prognostication as it relates to bilateral thyroid surgery and the safety of proceeding bilaterally, reducing rates of tracheotomy; (4) intraoperative prediction of impending neural injury with elettromiographic information allowing alteration of associated surgical maneuvers; (5) improved rate of identification and preservation of superior laryngeal nerve with monitoring as opposed to without; (6) a protocol involving electric neural monitoring testing of the vagus nerve facilitates early and definitive intraoperative identification of nonrecurrent laryngeal nerves; and (7) improvement of recurrent laryngeal nerve paralysis rate. Several notable studies regarding rates of recurrent laryngeal nerve paralysis with and without monitoring in discrete subgroups such as high-risk surgeries, surgeries for malignant diseases, and surgeries performed by low volume surgeons showed improved rates of recurrent laryngeal nerve paralysis. Monitoring in transoral endoscopic thyroidectomy vestibular approach (TOETVA) requires training. Surgeons and anesthesiologists must have accumulated high experience with intraoperative neural monitoring standards, equipments, troubleshooting algorithms, limits, and failures. It is unwise to use intraoperative neural monitoring for the first time with TOETVA, without any prior nerve monitoring experience. Standardized technique of intraoperative neural monitoring consists in identifying and monitoring both the vagus nerve and the recurrent laryngeal nerve before and after dissection (V1, V2, R1, and R2). There are many different types of stimulating devices used for intraoperative neuromonitoring of the recurrent laryngeal nerve during TOETVA. One of them is the stimulating probe used for open thyroidectomy. The surgeon stimulates percutaneously the vagal nerve and the recurrent laryngeal nerve through an incision made with the tip of the scalpel. Another method is using a long stimulating probe inserted through one of the two lateral 5 mm trocars. A third way consists in a modified endoscopic instrument or a modified energy-based device; in this way the tips of the device or the endoscopic instrument act as a stimulating probe. Finally a flexible wire probe can be used to stimulate the nerve; it is inserted through a trocar and then placed in position with the endoscopic instrument. Each one of these methods has its own pros and cons. The percutaneous probe for instance is way less expensive than the long probe, but requires higher stimulation intensity, another skin incision, and can produce a loss of CO2 insufflation. The modified endoscopic instrument or the modified energy-based device, in contrast, is not available in commerce although they seem to be more suitable solution. Trying to summarize the value of intraoperative neural monitoring during TOETVA we can say that it facilitates recurrent laryngeal nerve and superior laryngeal nerve identification; it enables testing of recurrent laryngeal nerve and superior laryngeal nerve function. Third, it enables corrective action at three stages of surgery: (I) during blunt dissection, (II) during use of energy-based devices, and (III) during thyroid gland retraction. Fourth, it enables evaluation of recurrent laryngeal nerve function by vagus nerve stimulation on one side before proceeding to the contralateral lobe. This advantage is particularly important for bilateral approaches. Last but not least intraoperative neural monitoring helps putting TOETVA in the same security area of open procedure as far as it concerned recurrent laryngeal nerve management.