CHAPTER 20 Thyroidectomy and Parathyroidectomy
THYROIDECTOMY
Case Study
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.
INDICATIONS FOR THYROID SURGERY
I. Suspicious or Symptomatic Thyroid Nodule: The workup of a solitary thyroid nodule typically includes an ultrasound, a thyroid scan, thyroid function tests, and FNA. In the vast majority of cases (70%), FNA reveals benign pathology (e.g., adenomatoid or hyperplastic lesions or colloid cysts). In approximately 15% of cases, FNA will be nondiagnostic. In the remaining 15% of cases, FNA is suspicious in 10% and consistent with malignancy (either primary thyroid cancer or metastatic disease) in 5%. Thyroid lobectomy is indicated after nondiagnostic or suspicious FNA findings in a patient with a symptomatic nodule or a concerning clinical history (e.g., a rapidly growing nodule or a significant radiation history). Importantly, 80% of patients with follicular neoplasms (i.e., suspicious lesions) are ultimately found to have benign adenomas; the remaining 20% are found to have follicular carcinomas. Typically, a thyroid lobectomy is performed after the diagnosis of a follicular neoplasm. If capsular or vascular invasion is present on the final pathology, establishing the diagnosis of a carcinoma, a completion thyroidectomy is performed. In a patient already receiving thyroid replacement hormone preoperatively, a total thyroidectomy is often recommended as the initial treatment.
II. Thyroid Cancer: Thyroid cancer types include papillary, follicular, medullary, and anaplastic. Thyroid lymphomas and metastatic disease to the thyroid are less common diagnoses. Papillary thyroid cancer is the most common type (80%–90%) in the United States and has an excellent prognosis (10-year survival rate, 90%–95%); it is characterized histologically by the presence of psammoma bodies (microscopic rounded collections of calcium) and optically clear nuclei (“Orphan Annie eyes”). Unlike papillary carcinoma, which when metastatic, usually spreads through the lymphatics to regional lymph nodes, follicular thyroid cancer metastasizes hematogenously to the lung and, less frequently, to bone. Generally, the management of these cancers includes total thyroidectomy followed by radioactive iodine ablation. En bloc resection of clinically palpable nodes and ipsilateral modified radical neck dissection, if these lymph nodes contain metastases, are also indicated. Medullary thyroid cancer develops from parafollicular cells and is often associated with MEN IIA, MEN IIB, and non-MEN familial syndromes. Treatment includes thyroidectomy with central lymph node dissection. Anaplastic thyroid cancer has a very poor prognosis, with a median survival of several months. Surgery has a limited role; radiation and chemotherapy are typically the primary treatment modalities.
MEN IIA: Pheochromocytoma, medullary thyroid cancer, and parathyroid hyperplasia
MEN IIB: Pheochromocytoma, medullary thyroid cancer, and paragangliomas
Non-MEN familial medullary thyroid cancer: Only medullary thyroid cancer
III. Goiter: The term goiter refers to benign enlargement of the thyroid gland. Surgery is generally reserved for patients with symptomatic or rapidly growing goiters.
IV. Toxic Nodule and Toxic Multinodular Goiter (TMG): Toxic nodules are most often follicular adenomas and are distinguished by the higher than normal uptake of radioactive tracer on thyroid scan (i.e., a hot nodule). Toxic multinodular goiters are characterized by the presence of several hot nodules. The descriptor toxic indicates excessive production of thyroid hormone. Although radioactive iodine is usually effective for the treatment of toxic nodules or TMG, surgery is indicated if radioactive iodine is contraindicated, or for the treatment of large symptomatic TMGs.
V. Graves’ Disease: Graves’ disease is a disorder caused by autoantibodies that bind the TSH receptor and stimulate excessive thyroid hormone secretion and hyperthyroidism. Symptoms include tachycardia, hypertension, diaphoresis, and weight loss. Additional manifestations of the disease include exopthalmos, which frequently does not improve with treatment, and pretibial myxedema. Initial treatment includes antithyroid medications, such as propylthiouracil and methimazole, which restore euthyroidism. Radioactive iodine therapy is then used to ablate the diseased thyroid gland. Surgery may be indicated in pregnant patients (in whom radioactive iodine is contraindicated), in children (in whom medical therapy is frequently ineffective), in patients who have been unsuccessfully treated with radioiodine, and when an underlying malignancy cannot be excluded. Typically, a near-total thyroidectomy is the procedure of choice. The remaining thyroid tissue protects against hypothyroidism, but may be associated with disease recurrence.
PREOPERATIVE EVALUATION
I. Thyroid function tests include T3, T4, and TSH levels. These tests allow for the diagnosis of hyperthyroidism or hypothyroidism.
II. Thyroid Ultrasound: Thyroid ultrasound is routinely obtained to better characterize thyroid nodules and help guide FNA of nodules that are not clinically evident.
III. Thyroid scan is a nuclear medicine study that can be used to characterize thyroid nodules on the basis of their functional activity. Radioactive tracer (99m-technetium pertechnetate, 123-iodine, or 131-iodine) is administered and is taken up by the thyroid gland. Nodules are characterized as hot (if they take up tracer at higher levels than normal thyroid tissue), cold (if they take up tracer at lower levels than normal thyroid tissue), or warm (if they take up iodine at levels similar to normal thyroid tissue).
COMPONENTS OF THE PROCEDURE AND APPLIED ANATOMY
I. Preoperative Considerations
A. Thyroidectomy is typically performed under general anesthesia; however, regional anesthesia (superficial cervical plexus block) and local anesthesia are alternatives in selected patients.
B. Preoperative preparation of patients with hyperthyroidism, including a medical regimen to achieve euthyroidism (propylthiouracil or methimazole) and control tachycardia and hypertension (β-blockade), significantly enhances the safety of surgery. In patients with ongoing symptomatic hyperparathyroidism, β-blockade should be continued throughout the perioperative period.
II. Patient Positioning and Preparation
A. The patient is placed in the supine position with the neck hyperextended; typically, a rolled sheet or other support is placed under the shoulders. The head is supported with a foam cushion that also serves to stabilize and prevent movement during the procedure.
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