Thyroidectomy and Parathyroidectomy

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CHAPTER 20 Thyroidectomy and Parathyroidectomy

THYROIDECTOMY

Case Study

A 48-year-old female presents to her primary care physician with a palpable mass in her right neck just lateral to the trachea. She denies neck pain, dysphagia, recent weight loss or gain, diaphoresis, palpitations, and previous radiation exposure.

Physical examination reveals a 3-cm nodule in the right thyroid lobe of her neck that moves with swallowing. There is no cervical or supraclavicular adenopathy. An ultrasound of the thyroid shows a dominant 2.6-cm nodule in the right lobe (Fig. 20-1). Results of thyroid function tests, including triidothyronine (T3), thyroxine (T4), and thyroid-stimulating hormone (TSH) levels, are all within normal limits. A fine-needle aspiration biopsy (FNA) of the nodule demonstrates cytology consistent with a follicular neoplasm.

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Figure 20-1 Thyroid ultrasound showing a large right thyroid nodule.

(From Townsend CM, Beauchamp RD, Evers BM, Mattox KL [eds]: Sabiston Textbook of Surgery: The Biological Basis of Modern Surgical Practice, 18th ed. Philadelphia, Saunders, 2008.)

BACKGROUND

The thyroid gland is a bilobed structure that develops from endoderm and descends during development into the neck from the base of the tongue. The thyroid gland is located anterior to the trachea, to which it is attached by the ligament of Berry, and below the thyroid cartilage. The thyroid receives its blood supply from the superior thyroid arteries (branches of the external carotid arteries) and the inferior thyroid arteries (branches of the thyrocervical trunks). Thyroid ima arteries, branches of the aorta, provide additional blood supply to the gland inferiorly. Venous drainage is via the superior, inferior, and middle thyroid veins. The bridge of tissue connecting the two thyroid lobes and overlying the trachea is called the isthmus. In some patients, thyroid tissue extends superiorly from the isthmus or the medial aspects of the thyroid lobes to form a pyramidal lobe.

The thyroid parenchyma consists of follicular cells, which store and are responsible for the organification of iodide, and parafollicular cells, derived from the neural crest, which produce the short-chain polypeptide calcitonin. Thyroid follicular cells couple inorganic iodide with tyrosine moieties to produce the more biologically active T3 hormone and the more abundant T4 hormone. Production and release of thyroid hormone is regulated by the hypothalamo-pituitary-thyroid axis through a negative feedback system. The principal stimulant of thyroid production is TSH, produced by the anterior pituitary. TSH production is inhibited by circulating thyroid hormone and stimulated by thyrotropin-releasing hormone from the hypothalamus.

INDICATIONS FOR THYROID SURGERY

COMPONENTS OF THE PROCEDURE AND APPLIED ANATOMY

Thyroidectomy and thyroid lobectomy are performed similarly, except that in the case of the latter, the isthmus is divided and only one thyroid lobe is removed. The basic goals of lobectomy and thyroidectomy include removal of the diseased thyroid and identification and preservation of the recurrent laryngeal nerves and parathyroid glands. Total thyroidectomy is discussed below.