Chapter Chapter 1 / Emergency Management: Evaluation of the Critically Ill or Injured Child • 114
21 Thyroid Gland
Surgical thyroid disease encompasses those condi- the cricothyroid membrane to innervate the abduc- tions in which partial or complete removal of the tor muscles of the true vocal cords. Injury during thy- thyroid gland is required due to goiter and hyper- roidectomy results in ipsilateral vocal cord paralysis thyroid conditions that are unresponsive to medical and subsequent hoarseness (Figure 21-2). management and to benign and malignant neoplastic As a result of aberrant migration of the develop- disease. ing thyroid gland, several anatomic variances can be seen. Complete failure of migration from the base of the tongue results in a lingual thyroid.The entire mass ANATOMY AND PHYSIOLOGY of thyroid tissue is located in the posterior tongue, and airway obstruction may result if goiter develops. The thyroid gland is derived embryologically from an Incomplete migration can result in thyroid tissue evagination of the floor of the pharynx at the base of being found anywhere between the base of the the tongue. The developing thyroid descends along a tongue and the root of the neck. Lastly, thyroid tissue midline course to its final position as a bilobed gland may migrate beyond the level of the thyroid cartilage overlying the lower half of the thyroid cartilage. The into the substernal region, where occasionally a sub- two lateral lobes of the fully developed gland are con- sternal goiter develops. nected by a median isthmus. In 75% of individuals, Persistence of the thyroglossal duct results in a thy- the distal thyroglossal remnant extends superiorly roglossal cyst or fistula. Thyroglossal cysts are most from the isthmus and is called the pyramidal lobe. commonly seen in children and appear as a single Arterial blood is supplied via the paired superior and painless lump in the midline that moves with swal- inferior thyroid arteries, and venous drainage is via lowing. Surgical excision of the cyst is corrective. the paired superior, middle, and inferior thyroid veins Thyroglossal duct fistulae appear as midline sinus (Figure 21-1). tracts. As the fistula is an embryologic remnant, it Of key importance to the surgeon is anatomic ascends superiorly through the middle of the hyoid knowledge of the recurrent laryngeal nerve. Bilateral bone, often to its origin at the base of the tongue. vagus nerves descend from the neck into the chest. Surgical excision of the fistula requires resection of The right vagus branches into the right recurrent the middle portion of the hyoid bone (Figure 21-3). laryngeal nerve, which loops under the right subcla- The thyroid gland determines the metabolic pace vian artery from anterior to posterior and ascends of the body. Increased levels of thyroid hormone and superiorly in the right tracheoesophageal groove. In loss of the normal negative feedback mechanism 5% of patients, the right laryngeal nerve may be non- result in hyperthyroidism. The main etiologies of recurrent, taking a more direct course into the larynx. hyperthyroidism are (a) diffuse toxic goiter (Graves’ The left vagus branches into the left recurrent laryn- disease), (b) toxic multinodular goiter (Plummer’s geal nerve, which loops in a similar anterior-to- disease), and (c) toxic adenoma. Surgical treatment posterior fashion around the arch of the aorta and of these disorders involves either excision of local- ascends along the left tracheoesophageal groove. The ized diseased tissue, as in the case of adenoma, or recurrent laryngeal nerves travel posteromedial to complete excision of the majority of the gland, as in their respective thyroid lobes and enter the larynx via Graves’ disease or toxic multinodular goiter. Chapter 21 / Thyroid Gland • 115
Superior laryngeal nerves
Carotid artery
Superior thyroid artery Internal jugular vein
Thyroid cartilage Superior parathyroid Thyroid
Middle thyroid vein
Inferior parathyroid Inferior thyroid artery Recurrent laryngeal Thyrocervical trunk nerve
Inferior thyroid veins
Brachiocephalic trunk
Figure 21-1 • Anatomy of the thyroid gland.
Traction sutures Upper parathyroid gland
Recurrent laryngeal nerve
Superior thyroid artery Suspensory ligament of Berry Inferior cornu of thyroid cartilage
Figure 21-2 • Course of the recurrent laryngeal nerve. 116 • Blueprints Surgery
Foramen caecum from the florid exophthalmos, dyspnea, and agitation of more advanced cases.
a 2 /3 1 Physical Examination b /3 Tongue c Patients are generally agitated, irritable, or nervous. The enlarged gland is palpable and often visibly Ectopic sites Hyoid bone apparent. Due to increased vascularity, a thrill may d a = Lingual thyroid be felt or a bruit auscultated over the enlarged lobes. b = Intralingual thyroid The most notable and dramatic finding is exoph- c = Sublingual thyroid d = Thyroglossal cyst thalmos, caused by edema of the retrobulbar fat pad e = Retrosternal thyroid forcing the globe anteriorly. Increased sympathetic Pyramidal lobe tone secondary to excess thyroid hormone causes eyelid retraction, leading to the pronounced Graves’ “stare.” Lateral lobe of thyroid Skin examination reveals myxedema, a raised e plaquelike skin change seen typically in a pretibial distribution. Cardiac examination demonstrates sinus Figure 21-3 • Migration of the thyroid via the thyroglossal duct tachycardia, hyperdynamism, systolic flow murmurs, and possible ectopic sites of development and duct remnants. and occasionally atrial fibrillation.