This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
In the case of hyperthyroidism which is the most common nerve to be damaged? 
Select and explain. 
A. Recurrent laryngeal nerve, B. Inferior laryngeal nerve, C. External branch of Superior laryngeal nerve, D. Internal branch of Superior laryngeal nerve
A: Recurrent laryngeal nerve
Answer: A: Recurrent laryngeal nerve 
Explanation: The recurrent laryngeal nerve innervates all intrinsic muscles of the larynx with exception of Cricothyroid muscle. Mechanisms of damage include complete or partial transection, traction, contusion and compromised blood supply. The consequence is true vocal fold paralysis.
The SLN has 2 divisions: internal and external. The internal branch provides sensory innervation to the larynx. It enters the larynx through the thyro-hyoid membrane and, therefore, should not be at risk during thyroidectomy. The external branch provides a motor function to the crico-thyroid muscle and is at risk during thyroidectomy.
This muscle is involved in elongation of the vocal folds. Trauma to the nerve results in an inability to lengthen a vocal fold and thus, an inability to create a high-pitched sound.