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.

An applied anatomical study on the recurrent laryngeal nerve and inferior thyroid artery.

PURPOSE: The aim of this study was to provide some important information about the morphology and topography of the recurrent laryngeal nerve (RLN) and inferior thyroid artery (ITA), which significantly helps localize and protect the RLN in neck surgery, especially in thyroid surgery. METHODS: Eighty adult cadavers (160 sides) fixed with formalin were dissected, analyzed and measured. RESULTS: (1) 87.5% of the RLNs gave off multiple branches like a tree; the incidence of the RLN loop, connecting one branch to another was 3.125%; in 9.375%, one branch of RLN combined with cervical sympathetic chain (CSC) or superior laryngeal nerve (SLN). (2) A double RLN appeared in four sides, a non-recurrent inferior laryngeal nerve appeared in two cases. (3) In two cases, the RLN communicated with both of the SLN and the CSC near thyroid gland. (4) Most of the ITAs was derived from thyrocervical trunk, and divided into two or three branches before entering the thyroid gland. (5) Three ITAs gave off esophageal branch, one ITA gave off tracheal branch, one right ITA originated abnormally. (6) On the left side, the RLN was behind the ITA in 86.25% of the cases, in front of the artery in 7.5%, the nerve was between artery branches in 2.5%, the artery was between nerve branches in 1.25%, and was among the combined in 2.5%. On the right side, the RLN was in front of the artery in 75.0%, behind the artery in 10.0%, among the branches of the artery in 5.0%, 10.0% the branches of both nerves and artery were interlaced that the relationship between the branches of the nerve and the artery was uncertain. CONCLUSIONS: Because of the variability of the RLN and ITA and the complicated relationship between them, it is necessary to dissect and recognize the RLN to avoid mistaking, ignoring, and misligating of the nerve before ligating the ITA.