Che-Wei Wu1,2, Min Hao3, Mengzi Tian3, Gianlorenzo Dionigi4, Ralph P Tufano5, Hoon Yub Kim6, Kwang Yoon Jung7, Xiaoli Liu8, Hui Sun8, I-Cheng Lu2,9, Pi-Ying Chang9, Feng-Yu Chiang10,11. 1. Department of Otolaryngology-Head and Neck Surgery, Kaohsiung Medical University Hospital, Kaohsiung Medical University, 100 TzYou 1st Road, Kaohsiung City, 807, Taiwan. 2. Faculty of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan. 3. Department of Breast Thyroid Surgery, The People's Hospital of Dong Ying, Shan Dong province, China. 4. 1st Division of Surgery, Research Center for Endocrine Surgery, Department of Surgical Sciences and Human Morphology, University of Insubria (Como-Varese), Varese, Italy. 5. Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, MD, USA. 6. Department of Surgery, Korea University College of Medicine, Seoul, South Korea. 7. Department of Otolaryngology-Head and Neck Surgery, Korea University College of Medicine, Seoul, South Korea. 8. Department of Thyroid and Parathyroid Surgery, China-Japan Union Hospital, Jilin Provincial Key Laboratory of Surgical Translational Medicine, Jilin University, Changchun, Jilin, China. 9. Department of Anesthesiology, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan. 10. Department of Otolaryngology-Head and Neck Surgery, Kaohsiung Medical University Hospital, Kaohsiung Medical University, 100 TzYou 1st Road, Kaohsiung City, 807, Taiwan. fychiang@kmu.edu.tw. 11. Faculty of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan. fychiang@kmu.edu.tw.
Abstract
PURPOSE: During monitored thyroidectomy, a partially or completely disrupted point of nerve conduction on the exposed recurrent laryngeal nerve (RLN) indicates true electrophysiologic nerve injury. Complete loss of signal (LOS; absolute threshold value <100 μV) at the end of operation often indicates a postoperative vocal cord (VC) palsy. However, the evaluation for the injured RLN with incomplete LOS and its functional outcome has not been well described. METHODS: Three hundred twenty-three patients with 522 RLNs at risk who underwent standardized monitored thyroidectomy were enrolled. The RLN was routinely stimulated at the most proximal (R2p signal) and distal (R2d signal) ends of exposure after thyroid resection to determine if there was an injured point on the RLN. Pre- and postoperative VC function was routinely examined. RESULTS: Twenty-nine RLNs (5.6 %) were detected with an injury point. Five nerves had complete LOS and other 24 nerves had incomplete LOS where the R2p/R2d reduction (% of amplitude reduction compared with proximal to distal RLN stimulation) ranged from 22 to 79 %. Postoperative temporary VC palsy was noted in those five RLNs with complete LOS (final vagal signal, V2 < 100 μV) and four RLNs with incomplete LOS (R2p/R2d reduction 62-79 %; V2 181-490 μV). In the remaining 20 nerves with R2p/R2d reduction ≤53 % (V2 373-1623 μV), all showed normal VC mobility. Overall, false negative results were found in two RLNs (0.4 %) featuring unchanged V2 and R2p/R2d but developed VC palsy. CONCLUSIONS: Testing and comparing the R2p/R2d signal is a simple and useful procedure to evaluate RLN injury after its dissection and predict functional outcome. When the relative threshold value R2p/R2d reduction reaches over 60 %, surgeon should consider the possibility of postoperative VC palsy.
PURPOSE: During monitored thyroidectomy, a partially or completely disrupted point of nerve conduction on the exposed recurrent laryngeal nerve (RLN) indicates true electrophysiologic nerve injury. Complete loss of signal (LOS; absolute threshold value <100 μV) at the end of operation often indicates a postoperative vocal cord (VC) palsy. However, the evaluation for the injured RLN with incomplete LOS and its functional outcome has not been well described. METHODS: Three hundred twenty-three patients with 522 RLNs at risk who underwent standardized monitored thyroidectomy were enrolled. The RLN was routinely stimulated at the most proximal (R2p signal) and distal (R2d signal) ends of exposure after thyroid resection to determine if there was an injured point on the RLN. Pre- and postoperative VC function was routinely examined. RESULTS: Twenty-nine RLNs (5.6 %) were detected with an injury point. Five nerves had complete LOS and other 24 nerves had incomplete LOS where the R2p/R2d reduction (% of amplitude reduction compared with proximal to distal RLN stimulation) ranged from 22 to 79 %. Postoperative temporary VC palsy was noted in those five RLNs with complete LOS (final vagal signal, V2 < 100 μV) and four RLNs with incomplete LOS (R2p/R2d reduction 62-79 %; V2 181-490 μV). In the remaining 20 nerves with R2p/R2d reduction ≤53 % (V2 373-1623 μV), all showed normal VC mobility. Overall, false negative results were found in two RLNs (0.4 %) featuring unchanged V2 and R2p/R2d but developed VC palsy. CONCLUSIONS: Testing and comparing the R2p/R2d signal is a simple and useful procedure to evaluate RLN injury after its dissection and predict functional outcome. When the relative threshold value R2p/R2d reduction reaches over 60 %, surgeon should consider the possibility of postoperative VC palsy.
Entities:
Keywords:
Electromyography; Intraoperative neuromonitoring; Loss of signal; Recurrent laryngeal nerve; Thyroid surgery
Authors: G Dionigi; P F Alesina; M Barczynski; L Boni; F Y Chiang; H Y Kim; G Materazzi; G W Randolph; D J Terris; C W Wu Journal: Surg Endosc Date: 2012-04-05 Impact factor: 4.584