An applied anatomical study on the external laryngeal nerve loop and the superior thyroid artery in the neck surgical region

This study was conducted to investigate the topographic relationship between the external laryngeal nerve (ELN) loop and the superior thyroid artery (STA), in order to provide the anatomical foundations for protecting the ELN during surgery. In the present study, 48 adult human cadavers were dissected and analyzed. For the 21 (21.9 %) low-position ELN loops observed, the neurovascular relationship between the STA and the nerve was classified into four types: (1) the artery overlapped the nerve; (2) the artery passed through the ELN loop; (3) the muscular branch of the ELN loop and the laryngeal branch of the STA coursed together; and (4) the branches of the STA and the ELN loop were interlaced. Our study suggested that the patterns of ELN loops are so complicated that they have not been statistically defined in any previous study, which should be kept in mind when attempting to protect the nerve from injury. Also, because of the variable morphology of the ELN loop and its complicated topographic relationship to the STA, the vessels should be individually isolated and then ligated during thyroidectomy. When ligating the laryngeal branch of the STA during larynx surgery, special attention should be paid to avoiding damage to the muscular branch of the ELN/ELN loop.