During thyroid surgery, injury to which nerve commonly causes hoarseness?

• A. Superior laryngeal nerve
• B. Recurrent laryngeal nerve
• C. Hypoglossal nerve
• D. Ansa cervicalis

Answer: (B)

In thyroid surgery, hoarseness is most commonly due to injury to the recurrent laryngeal nerve. This nerve, a branch of the vagus, travels in the tracheoesophageal groove and lies very close to the thyroid gland’s inferior vessels and Berry’s ligament, making it highly vulnerable during dissection and ligation. It supplies all intrinsic muscles of the larynx except the cricothyroid, so when one side is damaged, the affected vocal cord cannot move properly to adduct for phonation. The resulting glottic insufficiency produces a breathy, hoarse voice because the vocal cords on the injured side fail to close fully during speech. The left recurrent laryngeal nerve is particularly at risk because it loops under the aortic arch and has a longer intrathoracic course before ascending, but both sides can be endangered in thyroid procedures. By contrast, injury to the external branch of the superior laryngeal nerve mainly impairs tensioning of the vocal cords and can cause a high-pitched voice, not the classic hoarseness from glottic paralysis; the hypoglossal nerve would cause tongue weakness, and the ansa cervicalis would affect the strap muscles.