Anatomy and motor function of extra-laryngeal branching patterns of the recurrent laryngeal nerve; an electrophysiological study of 1001 nerves at risk.

INTRODUCTION

Safe thyroid surgery depends on a deep knowledge of human neck anatomy, including the recurrent laryngeal nerve (RLN). Anatomic variations such as extra-laryngeal terminal branching (ETB) are common.

PATIENTS AND METHODS

We studied the ETB pattern of 1001 RLNs at risk in 596 patients. We identified and exposed the location of division points on the cervical part of bifid RLN. The function of nerve branches was assessed through intraoperative nerve monitoring (IONM).

RESULTS

Bifid RLNs was identified in 39.6% of patients. The nerve-based prevalence of ETB was 28.5%. The prevalence of ETB for the right and left RLN was 21.8% and 35.5%, respectively ( < 0.001). The location of the division point was found in the middle, distal, and proximal segments in 48.8%, 33.3%, and 18% of bifid RLNs, respectively. Electrophysiological monitoring revealed motor functions in all anterior and in 7% of posterior branches. The rate of injury was 0.4%, and 1.1% in single trunk and bifid nerves, respectively ( = 0.360), and 3.9% in nerves with proximal branching ( = 0.084).

CONCLUSIONS

The ETB prevalence is high and showing division points in different cervical segments of the RLN. All anterior branches and some posterior branches contain motor fibers. Knowledge and awareness of these anatomic and functional variations are mandatory for every thyroid surgeon to avoid misidentification and misinterpretation of human RLN anatomy.