Necessity of Routinely Testing the Proximal and Distal Ends of Exposed Recurrent Laryngeal Nerve During Monitored Thyroidectomy

Abstract

ObjectivesIntraoperative neuromonitoring (IONM) is a useful tool to evaluate the function of recurrent laryngeal nerve (RLN) in thyroid surgery. This study aimed to determine the necessity and value of routinely testing the proximal and distal ends of RLN.MethodsIn total, 796 patients undergoing monitored thyroidectomies with standardized procedures were enrolled. All 1346 RLNs with visual integrity of anatomical continuity were routinely stimulated at the most proximal (R2p signal) and distal (R2d signal) ends after complete RLN dissection. The EMG amplitudes between R2p and R2d signals were compared. If the amplitude of R2p/R2d ratio reduction (RPDR) was over 10% or loss of signal (LOS) occurred, the exposed RLN was mapped to identify the injured point. Pre- and post-operative vocal cord (VC) mobility was routinely examined with video-laryngofiberscope.ResultsNerve injuries were detected in 108 (8%) RLNs, including 94 nerves with incomplete LOS (RPDR between 13%-93%) and 14 nerves with complete LOS. The nerve injuries were caused by traction in 80 nerves, dissecting trauma in 23 nerves and lateral heat spread of energy-based devices in 5 nerves. Symmetric VC mobility was found in 72 nerves with RPDR ≤50%. The occurrence of abnormal VC mobility (weak or fixed) was 14%, 67%, 100%, and 100% among the different RPDR stratifications of 51%-60%, 61%-70%, 71%-80%, and 81-93%, respectively. Of the 14 nerves with complete LOS, all showed fixed VC mobility. Permanent VC palsy occurred in 2 nerves with thermal injury.ConclusionRoutinely testing the proximal and distal ends of exposed RLN helps detect unrecognized partial nerve injury, elucidate the injury mechanism and determine injury severity. The procedure provides accurate information for evaluating RLN function after nerve dissection and should be included in the standard IONM procedure.

Comparison of EMG amplitudes recorded by ipsilateral and contralateral electrodes placement during using trans-thyroid cartilage recording method in thyroid surgery

“…The EMG amplitude measured at each step can reflect the functional status of the RLN. Theoretically, a decrease in EMG amplitude during surgery indicates a decreased number of muscle fibers participating in the polarization or a deficit of RLN function ( 22 , 23 ). Therefore, maintaining high and stable EMG amplitudes throughout the entire surgical procedure is important to help not only for RLN identification, but also for early detection of adverse EMG changes to prevent impending traction injury, quantitative analysis of amplitude change after RLN dissection, accurate prediction of vocal cord function outcome, avoidance of the occurrence of false LOS, and elucidation of the mechanism and severity of nerve injury.…”

Recent Advances in the Surgical Management of Thyroid Cancer

“…IONM helps to determine the exact location of RLN injuries and identify segments of neuropraxia [65]. This makes it possible to minimize the risk of bilateral RLN by delaying resection of the controlateral lobe when RLN injury is suspected after TL.…”

Proposals for Standardization of Intraoperative Facial Nerve Monitoring during Parotid Surgery

“…Since 2005, we have used neuromonitoring techniques for the RLN and FN as a routine setting in thyroid and parotid surgery. We first published the standardization of IONM of the RLN in thyroid surgery in 2010 [ 23 ] and the standardized procedures have been widely followed and included in international standard guidelines for RLN monitoring in thyroid surgery [ 24 , 25 , 26 , 27 ]. Inspired by advances in RLN monitoring over the past decade, this article will review the recent literature on FNM and present our (1) standards in FNM setup, (2) standards in general anesthesia, (3) standards in FNM procedures/application of stimulus currents, (4) interpretation of EMG signals/prediction of the facial expression outcome and (5) pre-/post-operative assessment of facial expressions.…”