The recurrent laryngeal nerve (RLN) is particularly prone to injury during thyroidectomy in case of extralaryngeal bifurcation being present in approximately one-third of patients near the inferior thyroid artery or ligament of Berry. Meticulous surgical dissection in this area may be additionally facilitated by the use of intraoperative neuromonitoring (IONM) to assure safe and complete removal of thyroid tissue. The aim of the study was to verify the hypothesis that meticulous surgical technique of tissue dissection in the area of the posterior surface of the thyroid capsule and adjacent RLN may be additionally facilitated by intraoperative neuromonitoring (IONM), and may contribute to increasing the safety and radicalness of total thyroidectomy in patients with well-differentiated thyroid cancer.
Material and methods: The outcomes of total thyroidectomy with level VI lymph node clearance for well-differentiated thyroid cancer (WDTC; pT1-3, N0-1, Mx) were retrospectively compared between 151 patients undergoing surgery with IONM (01/2005-06/2009) and 151 patients undergoing surgery without IONM (2003-2004). RLN morbidity (calculated for nerves at risk) was assessed by videolaryngoscopy or indirect laryngoscopy (mandatory before and after surgery and at 12-month follow-up). The anatomical course of the extralaryngeal segment of RLNs were analyzed in detail in each operation. Thyroid iodine uptake (131I) was measured during endogenous TSH stimulation test a week before radioiodine therapy.
Results: Among patients operated with vs. without IONM, the early RLN injury rate was 3% vs. 6.7% (p=0.02), including 2% vs. 5% (p=0.04) of temporary nerve lesions, and 1% vs. 1.7% of permanent nerve events (p=0.31), respectively. Extralaryngeal RLN bifurcation was identified in 42 (27.8%) vs. 25 (16.6%) of patients operated with vs. without IONM, respectively (p=0.001). Mean I-131 uptake following total thyroidectomy with vs. without IONM was 0.67 ± 0.39% vs. 1.59 ± 0.69% (p<0.001). 131I uptake lower than 1% was found in 106 (70.2%) vs. 38 (25.2%) patients operated with vs. without IONM, respectively (p<0.001).
Conclusions: Most patients with WDTC who undergo total thyroidectomy have a small amount of residual thyroid tissue. The use of IONM may improve the outcomes of surgery among these patients by both increasing the completeness of total thyroidectomy and significantly reducing the prevalence of temporary RLN injury. The possible mechanism of this improvement is the aid in dissection at the level of the Berry's ligament offered by IONM which enhances the surgeon's ability to identify a branched RLN, and allows for reduction of traction injury and neuropraxia of the anterior branch of bifid nerves.