From the Guidelines
The thyroid gland is surrounded by several important nerves, including the recurrent laryngeal nerve and the external branch of the superior laryngeal nerve, which must be carefully preserved during thyroid surgery to prevent voice changes and other complications. The recurrent laryngeal nerve, which runs behind the thyroid gland on both sides, controls vocal cord movement, and damage to this nerve can cause hoarseness or voice changes 1. The external branch of the superior laryngeal nerve, which lies near the superior thyroid vessels, controls the tension of the vocal cords, affecting voice pitch and quality 1. Other nerves, such as the vagus nerve and the sympathetic trunk, are also located near the thyroid gland and can be at risk during extensive dissections 1.
Key Nerves and Their Functions
- Recurrent laryngeal nerve: controls vocal cord movement
- External branch of the superior laryngeal nerve: controls the tension of the vocal cords, affecting voice pitch and quality
- Vagus nerve: gives rise to the recurrent laryngeal nerve and travels in the carotid sheath near the thyroid
- Sympathetic trunk: lies posteriorly and can be at risk during extensive dissections
Importance of Nerve Preservation
During thyroidectomy, surgeons use careful dissection techniques, nerve monitoring, and identification of anatomical landmarks to avoid nerve injury 1. Patients undergoing thyroid surgery should be informed about these nerves and potential complications, and surgeons typically perform preoperative and postoperative voice assessments to evaluate nerve function 1. The close relationship between these nerves and the thyroid gland explains why voice changes are a potential complication of thyroid surgery. Surgeons should take steps to preserve the external branch of the superior laryngeal nerve and identify the recurrent laryngeal nerve during thyroid surgery to minimize the risk of nerve injury and optimize voice outcomes 1.
From the Research
Nerves Located Around the Thyroid Gland
The nerves located around the thyroid gland include:
- The recurrent laryngeal nerve (RLN) which provides motor innervation to the abductor and adductor muscles of the vocal cord 2
- The external branch of the superior laryngeal nerve (EBSLN) which provides motor innervation to the cricothyroid muscle, the tensor muscle of the vocal cord 2, 3
- The paralaryngeal part of the vagal nerve 4
- The Ansa Galeni 4
- The delicate branches of the RLN to the posterior cricoarytaenoid muscle 4
Approaches to Identifying the Recurrent Laryngeal Nerve
There are four different approaches to identifying the RLN during thyroidectomy:
- Lateral approach: the most commonly used technique in primary thyroid surgery, where the RLN is usually found by dissection around the inferior thyroid artery at the level of the middle lobe of the thyroid 2
- Inferior approach: recommended for cases with secondary surgery, where the RLN is generally found at the site of its entry into the neck region devoid of scar formation 2
- Superior approach: recommended for patients with a huge goiter or large substernal goiter, where the upper pole of the thyroid is first released and then pulled forward and laterally, and the RLN is exposed on the nerve's entry point into the larynx, under the cricopharyngeus muscle 2
- Medial approach: preferred for patients with substernally or retropharyngeally enlarged goiters, where the isthmus is first dissected and divided, and then the isthmus and the medial part of the lobe are dissected away from the trachea to reveal the anterolateral part of the trachea 2
Importance of Preserving the Nerves
Preserving the anatomical integrity of the RLN and EBSLN is crucial to prevent vocal cord paralysis and other complications 2, 5, 3, 4, 6 Intraoperative neural monitoring (IONM) can be used to functionally assess the integrity of the RLN and EBSLN, and to prevent injuries to these nerves 2, 3