Thyroid surgery is a delicate procedure because several important structures are present near the thyroid gland that must be protected during the gland’s removal. One such structure is a tiny nerve that controls the movement of the vocal cord, called the recurrent laryngeal nerve. This nerve runs from the brain down to the chest before looping back up into the neck and the larynx (voice box). During its return course up through the neck, this delicate nerve runs directly against the back surface of the thyroid gland. If the nerve is disturbed during the removal of the gland, the result can be temporary (or in some cases even permanent) vocal cord paralysis. 

There are two separate nerves, one for each vocal cord, traveling along each side of the neck. Damage to one nerve can cause hoarseness or a weak voice, as well as coughing during swallowing, but this is usually temporary and improves as the nerve heals or the vocal cords adapt to the weakness. However, if both nerves are damaged during surgery, the result can be paralysis of the vocal cords and obstruction of breathing that can be life-threatening without placement of a surgical bypass of the airway, known as a tracheostomy. For this reason, the laryngeal nerve is always monitored with special electrodes during surgery to confirm its location and proper function. If a nerve is not functioning normally after the removal of one side of the thyroid gland, the surgery is aborted until a later date to allow the nerve to recover. This is also why total thyroidectomy is performed only when necessary to remove thyroid cancer.