J. C. Lee1,2, A. Kiu1, P. Chang1, J. Serpell1,2 1The Alfred Hospital,Department Of General Surgery,Melbourne, VICTORIA, Australia 2Monash University,Endocrine Surgery Unit,Melbourne, VICTORIA, Australia
Introduction: The identification and preservation of the recurrent laryngeal nerve (RLN) is paramount during thyroid surgery. Due to the slenderness of the branches, a RLN with an extralaryngeal bifurcation is at higher risk of intraoperative injury. When bifid, the motor fibres of a bifid RLN are located mainly in the anterior branch, and the sensory fibres in the posterior branch. However, it has not been documented whether the motor or sensory branch is likely to be thinner and therefore more prone to injury. This study aimed to measure the widths of the bifid RLN trunk and its branches, and to determine their possible associations with demographic factors.
Methods: This is a prospective observational study over 18 months at The Alfred Hospital, Melbourne, Australia, in patients undergoing thyroid surgery. The widths of the RLN trunk and branches were measured with Vernier calipers to the nearest 0.1 mm. Demographic data including age, gender, height, weight, and body mass index (BMI) were collected. Nerve widths were compared using Student’s t-test, and RLN widths and demographic data were correlated with Spearman correlation co-efficient (Stata 13).
Results: A total of 150 RLNs were eligible for inclusion during the 12-month study period. Of those, 34 bifid RLNs were identified in 32 patients, and therefore included in the analysis. The main RLN trunk had a mean width of 2.37 (range 1.7 – 4.0) mm. Whereas the mean widths for the anterior and posterior branches were 1.55 (0.8 – 2.5) mm and 1.33 (0.5 – 2.9) mm respectively. Both the anterior and posterior branches were significantly smaller than the main trunk (both p < 0.01). However, the branches were not statistically different from each other in their widths. Body weight and BMI positively correlated to the widths of both the anterior branch (p = 0.003 & p = 0.01 respectively) and posterior branch (p = 0.02 & p = 0.04 respectively). There was no correlation between age, height and either the main trunk or branches of the RLN.
Conclusion: As expected, the width of the RLN trunk is significantly greater than either of the branches of a bifid RLN. The knowledge of this may help alert the thyroid surgeon to the possibility of a bifid RLN during the process of dissecting along the RLN. More importantly, the similarity in the widths of the branches suggests that it is not possible to determine if a fine nerve branch is likely to be the anterior (motor) or posterior (sensory) branch. Low body weights or BMI may be a clue to possible delicate RLN branches.