Superior laryngeal nerve loop: patterns and surgical implications

This study clarifies the patterns of the superior laryngeal nerve loop (SLN loop), connecting the cervical sympathetic chain (CSC) and the SLN and its branches, so as to provide an anatomic basis for decreasing the risk of injury to the external laryngeal nerve (ELN) during neck surgery. Fifty Chinese adult human cadavers fixed with 4 % formalin were dissected, and their SLN loop patterns were analyzed and summarized. In 98 of 100 sides the CSC anastomosed with the SLN and its branches, forming a looped nerve structure which we called the SLN loop. The SLN loops could be divided into five types: e ( n ), t ( n ), i ( n ), t ( n ) e ( n ), and i ( n ) e ( n ) based on morphological variations. The results demonstrated that e ( n ) was most frequently found in the samples (82/100) followed by t ( n ) (9/100), i ( n ) (3/100), t ( n ) e ( n ) (2/100), and i ( n ) e ( n ) (2/100). Comparing with the previous work, we identified additional 18 subtypes of the SLN loop. The relations of the SLN loop to the surrounding structures were complicated, which brought more challenges to thyroidectomy. Thus, we do not advocate routine identification of ELN/ELN loop during the process of thyroidectomy, especially systematic identification of ELN during operation. However, this study introduces the possibility that nerve injury can be avoided by exposure of the nerve via careful dissection in the region of the superior pole of the thyroid gland to the extent that we can initiate individual ligation of the superior polar vessels, along with the help of neuromonitors, video monitors, and magnifying loupes.