The mechanism of recurrent laryngeal nerve injury during thyroid surgery--the application of intraoperative neuromonitoring.
BACKGROUND
Identification of recurrent laryngeal nerve (RLN) has decreased the rates of permanent RLN palsy during thyroid operations; however, unexpected RLN palsy still occurs, even though the visual integrity was assured and most nerve injuries were not recognized intraoperatively. The aim of this study is to determine the causes of RLN palsy and to identify potentially reversible causes of RLN injury during the operation with the application of intraoperative neuromonitoring (IONM).


METHODS
One hundred and thirteen patients with 173 nerves at risk were enrolled in this study. All operations were performed by the same surgeon. The 4-step procedure of IONM was designed to obtain electromagnetic (EMG) signals from the vagus nerve and RLN before and after resection of thyroid lobe.


RESULTS
Sixteen nerves had loss of EMG signals after thyroid dissection, and the causes of nerve injuries were well elucidated with the application of IONM. One nerve injury was caused by inadvertent transection, which led to permanent RLN palsy. Among the remaining 15 nerves, 1 injury was caused by a constricting band of connective tissue, which was detected precisely and released intraoperatively, 2 by inadvertent clamping of the nerve, and 12 by apparent overstretching at the region of Berry's ligament. (Five nerves regained signals before closing the wound, but 1 showed impaired cord movement. Another 7 nerves did not regain signals before closing the wound, and all developed temporary RLN palsy.)


CONCLUSIONS
Our 4-step procedure of IONM is useful and helpful in elucidating the potential operative pitfalls during dissection near the RLN. Although the rates of RLN palsy were not decreased in this study, the use of neuromonitoring provided instructive information for future operations by ascertaining where and how the RLN has been injured.
Chiang
Feng-Yu
FY
Department of Otolaryngology-Head and Neck Surgery, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan.
Lu
I-Chen
IC
Kuo
Wen-Rei
WR
Lee
Ka-Wo
KW
Chang
Ning-Chia
NC
Wu
Che-Wei
CW
D000328:Adult; D000368:Aged; D055590:Electromagnetic Phenomena; D005260:Female; D006801:Humans; D007431:Intraoperative Complications; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D009431:Neural Conduction / Q000502:physiology; D012009:Recurrent Laryngeal Nerve / Q000503:physiopathology; D013961:Thyroid Gland / Q000601:surgery; D013965:Thyroidectomy / Q000009:adverse effects*; D014630:Vagus Nerve / Q000502:physiology; D014826:Vocal Cord Paralysis / Q000175:diagnosis* / Q000209:etiology* / Q000503:physiopathology