A 58-year-old woman presents with a 2-week history of persistent hoarseness. She underwent a total thyroidectomy for a multinodular goiter three weeks ago. She denies any pain, fever, or difficulty swallowing, but she notes that her voice feels weak and breathy, and she occasionally coughs when drinking water. On physical examination, her voice is noticeably raspy. Flexible fiberoptic laryngoscopy reveals that the left vocal fold remains in a paramedian position during both phonation and inspiration.
Which of the following nerves was most likely injured during her surgery?
The correct answer is:
C) Left recurrent laryngeal nerve
Vocal fold paralysis following thyroid or parathyroid surgery is most often due to injury of the recurrent laryngeal nerve (RLN). The RLN provides motor innervation to all the intrinsic muscles of the larynx except for the cricothyroid muscle. When one RLN is injured, the affected vocal fold typically rests in a paramedian position. This prevents complete glottic closure during phonation, leading to a breathy, weak voice, which is sometimes described as hoarseness. Furthermore, the inability to fully close the glottis increases the risk of aspiration, particularly with liquids, explaining the patient's coughing while drinking. The left RLN is more commonly injured than the right because it has a longer, more convoluted course, looping under the arch of the aorta before ascending in the tracheoesophageal groove.
Answer choice A: External branch of the superior laryngeal nerve, is incorrect. This nerve innervates the cricothyroid muscle, which tenses the vocal folds to increase pitch. Injury leads to a subtle deepening of the voice or an inability to produce high-pitched sounds, but not true paralysis of the vocal fold.
Answer choice B: Internal branch of the superior laryngeal nerve, is incorrect. This nerve provides sensory innervation to the larynx above the vocal folds. Injury would lead to a loss of the cough reflex but not vocal fold immobility.
Answer choice D: Right recurrent laryngeal nerve, is incorrect. While the right recurrent laryngeal nerve can certainly be injured during thyroid surgery, the question specifies that the left vocal fold is paralyzed.
Answer choice E: Spinal accessory nerve, is incorrect. This nerve (CN XI) innervates the sternocleidomastoid and trapezius muscles. Injury would result in shoulder droop and difficulty with neck rotation, not hoarseness.
Key Learning Point
Unilateral recurrent laryngeal nerve injury causes hoarseness and a breathy voice due to vocal fold paralysis in the paramedian position. Bilateral recurrent laryngeal nerve injury is a surgical emergency. While the voice may actually be preserved since the cords are close together, the airway is severely compromised because the cords cannot open during inspiration, often requiring an immediate tracheostomy.
