A 54-year-old woman is evaluated for a painless thyroid nodule. She has had no weight changes, heat or cold intolerance, hoarseness, or dyspnea. Medical history is notable for mild hypertension, for which she takes appropriate medications. The patient does not use tobacco or alcohol. Physical examination shows a 3-cm, firm nodule in the right thyroid lobe and enlarged, right cervical lymph nodes. TSH is normal, and fine-needle aspiration of the nodule shows papillary structures with nuclear atypia. Total thyroidectomy is planned. During the surgery, a nearby nerve is injured while ligating an artery entering the superior pole of the thyroid lobe. Which of the following muscles is most likely to be denervated as a result of this injury?

Question

A 54-year-old woman is evaluated for a painless thyroid nodule.  She has had no weight changes, heat or cold intolerance, hoarseness, or dyspnea.  Medical history is notable for mild hypertension, for which she takes appropriate medications.  The patient does not use tobacco or alcohol.  Physical examination shows a 3-cm, firm nodule in the right thyroid lobe and enlarged, right cervical lymph nodes.  TSH is normal, and fine-needle aspiration of the nodule shows papillary structures with nuclear atypia.  Total thyroidectomy is planned.  During the surgery, a nearby nerve is injured while ligating an artery entering the superior pole of the thyroid lobe.  Which of the following muscles is most likely to be denervated as a result of this injury?

Quizplus · Accepted Answer

11ec160b_3571_bbfe_9249_bb0642ddc9d3_MD0001_00 The superior thyroid artery (a branch of the external carotid artery) and the inferior thyroid artery (a branch of the thyrocervical trunk) provide the blood supply to the thyroid and parathyroid glands. The superior thyroid artery and vein and external branch of the superior laryngeal nerve course together in a neurovascular triad that originates superior to the thyroid gland and lateral to the thyroid cartilage. The external branch is at risk of injury during thyroidectomy as it courses just deep to the superior thyroid artery. The cricothyroid muscle is the only muscle innervated by this nerve. It originates on the cricoid cartilage and inserts on the lower border of the thyroid cartilage. The cricothyroid muscle acts to tense the vocal cords, and denervation injury may cause a low, hoarse voice with limited range of pitch. The internal branch of the superior laryngeal nerve does not innervate any muscles but provides sensory innervation to the laryngeal mucosa above the vocal folds. (Choices A, C, D, and E) The remaining laryngeal muscles are innervated by the recurrent laryngeal nerves, which also provide sensory innervation to the larynx below the vocal folds. The recurrent laryngeal nerves lie posterior to the thyroid, near the inferior thyroid arteries. These nerves can be injured during thyroidectomy but do not run with the superior thyroid artery at the superior pole of the thyroid. Educational objective: The external branch of the superior laryngeal nerve is at risk of injury during thyroidectomy due to its proximity to the superior thyroid artery and vein. This nerve innervates the cricothyroid muscle. __________ References: Identification of the external branch of the superior laryngeal nerve during thyroidectomy. (http://www.ncbi.nlm.nih.gov/pubmed/19380357)

A 54-Year-Old Woman Is Evaluated for a Painless Thyroid Nodule