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.
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
III. Incision: An incision is made one to two fingerbreadths above the sternal notch following Langer’s lines, centered in the midline. The length of the incision is influenced by the patient’s body habitus and the size of the thyroid gland.
IV. Exposure
A. Dissection is carried down through the subcutaneous tissue and the platysma muscle. Flaps are raised superiorly and inferiorly in the avascular plane, just beneath the platysma muscle, superficial to the anterior jugular veins.
B. The vertical plane between the strap muscles (sternohyoid and sternothyroid muscles) is developed up to the thyroid cartilage and down to the sternal notch. The strap muscles are retracted laterally. The loose areolar tissue just deep to the sternothyroid muscles is dissected using electrocautery to expose the thyroid gland (Fig. 20-2).
V. Dissection
B. Gentle medial traction is placed on the ipsilateral gland, allowing for exposure of the vessels to the superior pole. Care is taken when dividing these vessels to dissect in a medial to lateral direction to minimize potential injury to the external branch of the superior laryngeal nerve.
C. After division of the superior pole vessels, the gland is retracted further medially, allowing for improved exposure of the inferior pole. The recurrent laryngeal nerve (RLN), which typically resides in the tracheoesophageal groove, just posterior to the inferior thyroid artery, is identified.
E. During dissection, the parathyroid glands are identified and preserved if possible. This is particularly important during total thyroidectomy, in which the risk of postoperative hypoparathyroidism is increased. Reimplantation of inadvertently removed parathyroid glands into the sternocleidomastoid muscle may help to reduce the incidence of this complication.
VI. Closure: The wound is thoroughly irrigated and hemostasis is confirmed. The strap muscles and platysma are reapproximated. The skin is closed using a running suture.
VII. Additional Operative Considerations
A. Drainage: Closed-suction drainage is often unnecessary following thyroid lobectomy. Although it is not a substitute for achieving meticulous hemostasis following resection, placement of a drain may be helpful in patients after total thyroidectomy, particularly for large goiters, to limit seroma formation.
COMPLICATIONS
I. Although significant bleeding after thyroid surgery is relatively uncommon (<1%), patients should be closely monitored for signs of hematoma formation. An expanding neck hematoma associated with dyspnea or stridor suggests impending airway compromise. In the presence of these signs and symptoms, the neck incision should be opened at the bedside, the hematoma evacuated, and the patient promptly returned to the operating room.
II. Injury to the RLN is a rare complication of thyroid surgery (<1). Unilateral RLN injury may lead to vocal cord paresis and medialization of the cord (clinically manifested as voice hoarseness). After total thyroidectomy, bilateral RLN injury can lead to airway occlusion.
III. The superior laryngeal nerve has two branches: the internal (which provides sensory innervation to the larynx) and the external (which provides motor innervation to the cricothyroideus muscle). The external branch of the nerve is closely associated with the superior thyroid artery and may be injured during mobilization of the upper thyroid poles. Injury may result in loss of vocal projection, particularly at higher pitches.
IV. Hypoparathyroidism with associated hypocalcemia may result from removal or devascularization of the parathyroid glands. Hypocalcemia may be detected clinically by tapping on the facial nerve in the preauricular area to elicit facial twitching (Chvostek’s sign) or inflating a blood pressure cuff to elicit carpal spasm (Trousseau’s sign). Hypocalcemia should be treated with calcium supplementation.
V. Thyroid storm is a rare complication of thyroid surgery in patients with hyperthyroidism (e.g., Graves’ disease). In the anesthetized patient, thyroid storm may manifest as tachycardia or cardiac arrhythmias and hyperthermia. Immediate cessation of the operative procedure is indicated, in conjunction with β-blockade (propanolol), antithyroid medications (propylthiouracil), corticosteroids, and iodine.
PARATHYROIDECTOMY
Case Study
A sestamibi scan is obtained and shows increased uptake in the left side of the neck (Fig. 20-4).
INDICATIONS FOR PARATHYROID SURGERY
I. Primary Hyperparathyroidism
A. Most cases of primary hyperparathyroidism (80%–85%) are due to single adenomas; the remaining cases are due to multiglandular hyperplasia (10%–15%) or double adenomas (5% to 10%). Although most often sporadic, multiglandular disease can be associated with familial syndromes, such as MEN I and MEN IIA. Parathyroidectomy is indicated in patients with symptomatic primary hyperparathyroidism or in asymptomatic patients who meet the following criteria (per the 2002 National Institutes of Health consensus guidelines):
B. Surgical resection of aberrant parathyroid tissue cures primary hyperparathyroidism. In patients with single or double adenomas, surgery consists of the removal of the abnormal gland(s). In patients with multiglandular hyperplasia, surgery involves either a subtotal (3.5 glands) parathyroidectomy or total parathyroidectomy with autotransplantation of parathyroid tissue into the sternocleidomastoid muscle or brachioradialis muscle of the forearm.
II. Secondary Hyperparathyroidism: The majority of patients with secondary hyperparathyroidsim are treated medically. Occasionally, patients require surgery for refractory bone pain or fractures and generally undergo a subtotal parathyroidectomy or total parathyroidectomy with autotransplantation of parathyroid tissue.
III. Tertiary Hyperparathyroidism: Patients with tertiary hyperparathyroidism almost invariably have multiglandular disease and frequently benefit from surgery with either a subtotal parathyroidectomy or total parathyroidectomy with autotransplantation.
IV. Parathyroid cancer accounts for fewer than 0.1% of cases of primary hyperparathyroidism and is often associated with extremely high calcium levels or, in some instances, hypercalcemic crisis (characterized by severe neurologic, gastrointestinal, and renal symptoms). Treatment of severe hypercalcemia involves intravenous fluid resuscitation, loop diuretics, bisphosphonates, calcitonin, and occasionally dialysis, if other measures prove unsuccessful. The finding of a palpable neck mass in a patient with primary hyperparathyroidism should raise suspicion for the diagnosis of parathyroid carcinoma. Treatment of a parathyroid carcinoma includes excision of the tumor with en bloc thyroid lobectomy and removal of associated cervical lymph nodes.
PREOPERATIVE EVALUATION
I. Serum calcium levels are typically checked on at least two occasions to verify hypercalcemia. Frequently, either an ionized calcium level or a calculated calcium level corrected for the patient’s serum albumin level is also obtained.
II. Serum PTH level is typically elevated, or higher than anticipated for the corresponding calcium level, in patients with primary hyperparathyroidism.
III. Vitamin D (1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]) level can help to identify patients with mild hyperparathyroidism and vitamin D deficiency who may benefit from vitamin D supplementation.
IV. Twenty-four-hour urine calcium levels help to determine whether an asymptomatic patient meets the criteria for parathyroid surgery and exclude the diagnosis of familial hypercalcemic hypocalciuria (FHH). Patients with FHH will typically have a normal PTH level, with mildly elevated calcium levels and paradoxically low urinary calcium levels. Such patients do not benefit from parathyroidectomy.
V. Technetium-99m sestamibi scanning can localize an abnormal parathyroid gland (distinguished on the basis of enhanced tracer uptake). The sensitivity of the scan is limited (60%–90%), although a negative finding is associated with a higher incidence of multiglandular disease.
VI. High-resolution ultrasound can be helpful in identifying an enlarged parathyroid gland and has a sensitivity of 60% to 80%. In combination with sestamibi scanning, the specificity of abnormal parathyroid gland localization is greater than 90%.
VII. Computed tomography (CT) scan and magnetic resonance imaging (MRI) are not routinely obtained before parathyroid surgery, although they may be helpful in patients who require reoperative parathyroid surgery.
VIII. Selective venous sampling of PTH levels is not routinely performed before parathyroid surgery, but may be helpful in reoperative cases in which other imaging modalities do not localize the abnormal gland. Blood from both jugular veins at multiple levels is sampled, and the concentration gradient of PTH may help to localize the lesion.
COMPONENTS OF THE PROCEDURE AND APPLIED ANATOMY
I. Preoperative Considerations: Conventional parathyroidectomy involves bilateral neck exploration with visualization of all four parathyroid glands (and sometimes biopsy of normal-appearing glands to exclude multiglandular disease). Increasingly, surgeons are adopting minimally invasive parathyroidectomy (MIP). In this approach, a unilateral dissection is performed on the side of the localized abnormal gland. This approach is associated with shorter operative times and a decreased risk of recurrent laryngeal nerve injury. Intraoperative parathyroid hormone monitoring with the rapid PTH immunoassay has emerged as an important adjunct to this approach. Because of the short half-life of PTH (approximately 3 minutes), a PTH level can be sent 10 to 15 minutes after resection of the suspected abnormal gland. A drop by more than 50% from the baseline level (i.e., serum PTH level before dissection and gland manipulation) and to the normal range suggests curative resection. Conversely, failure of PTH levels to normalize after resection of an abnormal gland should raise suspicion for the presence of additional disease and prompt further exploration.
II. Patient Positioning and Preparation
III. Incision: Parathyroidectomy is performed through a cervical collar incision following the Langer’s lines 1 to 2 cm above the sternal notch. Small skin incisions of 2 to 4 cm are the hallmark of minimally invasive parathyroidectomy.
IV. Exposure
A. Dissection is carried down through the subcutaneous tissue and the platysma muscle. Flaps are raised superiorly and inferiorly in the avascular plane, just beneath the platysma muscle, superficial to the anterior jugular veins.
B. The vertical plane between the strap muscles (sternohyoid and sternothyroid muscles) is developed up to the thyroid cartilage and down to the sternal notch. The strap muscles are retracted laterally. The loose areolar tissue just deep to the sternothyroid muscles is dissected using electrocautery to expose the thyroid gland (Fig. 20-5).
V. Dissection
A. The position of the superior parathyroid glands is more predictable than that of the inferior glands; they are usually located just superior to the inferior parathyroid artery. After identification, the gland is dissected free from the thyroid and other adjacent tissue. The gland’s vascular pedicle is then clipped or ligated and divided.
B. The inferior parathyroid glands are more variable in position, although they are most commonly found at the inferolateral aspect of the thyroid in the region of the thyrothymic ligament. As with the superior gland, great care should be taken to dissect the gland free without injuring the recurrent laryngeal nerve.
VI. Closure: The neck wound is thoroughly irrigated, and hemostasis is confirmed. The strap muscles and platysma are reapproximated. The skin is then closed using a running suture.
VII. Additional Operative Considerations: Ectopic parathyroid glands may be located within the thymus gland, in the carotid sheath, in the thyroid gland, low in the tracheoesophageal groove, or elsewhere in the mediastinum (Fig. 20-6). Intraoperative ultrasound is sometimes helpful in the identification of ectopic glands, including those that are intrathyroidal. When an abnormal gland cannot be identified during neck exploration, transcervical thymectomy may be considered. If exhaustive efforts to locate the abnormal gland are unsuccessful, the patient should undergo cross-sectional imaging studies (e.g., CT scan or MRI). In some cases, reoperation through a sternotomy is necessary to remove a mediastinal ectopic parathyroid gland.
COMPLICATIONS
II. Injury to the recurrent laryngeal nerve is a very rare complication of parathyroidectomy. A benefit of MIP surgery for localized parathyroid disease is that dissection is limited to one side of the neck, precluding the possibility of bilateral RLN injury.
III. Temporary hypocalcemia may be seen in up to 30% of patients after parathyroidectomy. After total parathyroidectomy and autotransplantation, rarely, patients have refractory hypocalcemia requiring long-term intravenous calcium supplementation. Cryopreservation of parathyroid tissue at the time of parathyroidectomy, if feasible, may allow for subsequent reautotransplantation.
