The Superior Laryngeal Nerve and its Vulnerability in Surgeries of the Neck

Abstract

Knowledge of anatomical considerations of the superior laryngeal nerve, a branch of the vagus, provides information to prevent intraoperative injuries and associated dysfunctions. The superior laryngeal nerve has external and internal branches providing motor innervation to the cricothyroid muscle and sensory innervation to the supraglottic mucosa of the larynx, respectively. The external laryngeal branch travels for a relatively greater distance together with the superior thyroid artery and the internal laryngeal branch accompanies, for a shorter distance, the superior laryngeal artery, though their relationship with their respective artery varies. Isolation and identification of the superior pole and superior laryngeal vessels, which are intimately related to the external and internal laryngeal branches, respectively, is clinically important. Both branches can potentially be severed, compressed, or stretched during surgical procedures of the neck such as thyroidectomy and anterior cervical discectomy. Injury to the external laryngeal nerve results in a reduction in the highest attainable frequency of the voice, while injury to the internal laryngeal nerve results in a loss of sensation in the laryngeal vestibule, increasing the risk of aspiration pneumonia. The consequences of superior laryngeal nerve injury are variable in growing literature and are commonly disregarded compared to the recurrent laryngeal nerve. The present study aims to assess the anatomical considerations of the superior laryngeal nerve pertaining to its course and relationship to the superior thyroid and superior laryngeal arteries. The study was done on 35 formalin‐fixed cadavers at Oakland University William Beaumont School of Medicine in 2018–2020. Following critical observation and careful dissection, photographs were taken and the data was analyzed quantitatively and in a descriptive manner. In our investigation, we found that out of twenty‐one cadavers, 52.4% of the external laryngeal branches are related posteromedial to the superior thyroid artery, while 47.6% are related anteromedial to it. On the other hand, our findings indicate that out of fourteen cadavers, 64.3% of the internal laryngeal branches are related superoposterior to the superior laryngeal artery, while 35.7% are inferoposterior to it. In addition, in most cases, the superior laryngeal artery crosses above the external laryngeal branch while traveling to pierce the thyrohyoid membrane to reach the larynx. The data portrays that both the external and internal laryngeal branches display a variation in their relationship with the superior thyroid artery and the superior laryngeal artery. The findings show a clinically important variation in the course and relationship of the superior laryngeal nerve and its related vessels, especially the posteromedial and superoposterior relationships, which exposes the nerves during ligation of the respective vessels. Awareness of these variable relationships is critical for identification and isolation of the neurovascular structures in order to preserve the nerve, prevent a reduction in the highest attainable frequency of the voice, and minimize the risk of aspiration pneumonia during surgical procedures of the neck.