A 52-year-old woman is evaluated in the recovery room following a total thyroidectomy for a large multinodular goiter. The surgical report indicates that the procedure was challenging due to the size of the gland and significant adherence to the surrounding tissues, particularly near the inferior thyroid artery. In the recovery area, the patient is noted to have a new, breathy hoarseness when speaking to her family. She denies any numbness or tingling in her hands or around her mouth. Her temperature is 37.0 C (98.6°F), blood pressure is 124/82 mmHg, pulse is 80/min, and respirations are 14/min. Physical examination of the neck shows a clean dressing without evidence of an expanding hematoma. She is able to swallow sips of water without coughing. Indirect laryngoscopy demonstrates the right vocal cord in a fixed, paramedian position during both inspiration and phonation.
Injury to which of the following nerves is the most likely cause of this patient's symptoms?
The correct answer is:
D) Recurrent laryngeal nerve
The recurrent laryngeal nerve provides motor innervation to all the intrinsic muscles of the larynx except for the cricothyroid muscle. During a thyroidectomy, this nerve is at risk of injury due to its close anatomical proximity to the inferior thyroid artery and its course behind the thyroid lobes. Unilateral injury to the recurrent laryngeal nerve leads to paralysis of the ipsilateral vocal cord, which typically assumes a paramedian position. This results in a breathy voice or hoarseness because the vocal cords cannot approximate perfectly during phonation. While the contralateral cord may eventually compensate, the acute presentation is typically a change in voice quality without significant respiratory distress. If the injury were bilateral, both vocal cords would be fixed in a paramedian position, which significantly narrows the glottis and would present as acute respiratory distress and inspiratory stridor, often requiring an emergency airway.
Answer choice A: External branch of the superior laryngeal nerve, is incorrect. This nerve provides motor innervation only to the cricothyroid muscle, which functions to tense the vocal cords and increase the pitch of the voice. Injury to this nerve typically results in a subtle voice change, specifically the inability to produce high-pitched sounds or easy vocal fatigue, but it does not cause vocal cord paralysis or a fixed paramedian position.
Answer choice B: Glossopharyngeal nerve, is incorrect. The glossopharyngeal nerve (CN IX) provides sensory innervation to the posterior third of the tongue and the oropharynx, and motor innervation to the stylopharyngeus muscle. Injury would lead to a loss of the gag reflex or difficulty swallowing but would not affect vocal cord mobility.
Answer choice C: Internal branch of the superior laryngeal nerve, is incorrect. This nerve provides purely sensory innervation to the laryngeal mucosa above the level of the vocal cords. Injury to this nerve would result in a loss of the cough reflex when foreign material enters the supraglottic area, increasing the risk of aspiration, but it would not cause hoarseness or vocal cord paralysis.
Answer choice E: Vagus nerve proximal to the superior laryngeal branch, is incorrect. While the recurrent laryngeal nerve is a branch of the vagus nerve, an injury this proximal would result in the loss of function of both the superior laryngeal nerve and the recurrent laryngeal nerve. This would likely cause more significant symptoms, including dysphagia due to pharyngeal branch involvement, and the paralyzed vocal cord would typically be in a more abducted or cadaveric position rather than the paramedian position described.
Key Learning Point
Unilateral injury to the recurrent laryngeal nerve is a potential complication of thyroid surgery and presents as hoarseness due to vocal cord paralysis in a paramedian position. Bilateral injury to the recurrent laryngeal nerve is a surgical emergency that presents with acute inspiratory stridor and airway obstruction.
