Open Neck Thyroid and Parathyroid Surgery
The great Greek physicians Hippocrates and Galen defined disease as a natural process and based treatment on observation and experience. Hippocrates is credited with naming cancer as karkinoma (carcinoma) because a tumor looked like a “crab” with its blood vessels extending from a hard, solid body like legs. The pain of cancer was also likened to the pinch of a crab. Galen used oncos to describe all tumors, the root for the modern word oncology. These visionary scientists believed that a tumor may arise from too much blood in the veins, or a flux of black bile mixed with blood producing a scirrhus, a tumor that could transmute into cancer. Cancers were identified, with warnings against treatment of the more severe forms. This approach set the template for Islamic medicine, which rapidly spread throughout the Arab Empire. Rhazes, the great Persian physician, warned that surgery generally made matters worse unless the tumor was completely removed and the incision was cauterized, while Paré confessed that he had never seen cancer cured by the knife. We have come a long way in terms of surgical oncology and tumor ablation but complications and morbidity are daily consequences of surgical adventure and ingenuity.
The American Cancer Society estimated that 46,670 new cases of thyroid cancer would be diagnosed in 2010 (American Cancer Society 2010). Surgical ablation is the main treatment of thyroid tumors within the thyroid bed and surrounding central and lateral lymphatic drainage basins. Thyroid tumors represent a fascinating group of heterogeneous neoplasms. Thyroid cancer is broadly divided into differentiated and undifferentiated cancers. Papillary and follicular carcinoma (well-differentiated thyroid carcinomas) arise from the follicular epithelium and are the most common thyroid malignancies. Thyroid differentiated cancers are followed by medullary thyroid carcinoma, anaplastic thyroid carcinoma and thyroid lymphoma (according to traditional teaching). A rare form of thyroid cancer would be metastases from breast or colon disease.
The male to female ratio is ~ 2.5: 1, but this may be a conservative estimate. Presentation is largely during the fourth to fifth decades of life with a median age at presentation of 47 years. A thyroid nodule is the usual presenting feature of a thyroid neoplasm, with 275,000 new nodules detected annually in the United States.1 An increasing number of incidental thyroid nodules are being identified through the use of ultrasonography by primary-care physicians. In general, the majority of patients with well-differentiated thyroid carcinoma have a favorable long-term prognosis with 10-year survival exceeding 90%. Several prognostic factors have been identified to segregate patients with well-differentiated thyroid carcinoma into a large group with a low risk of mortality and a small group with a high risk of mortality. At Memorial Sloan Kettering Cancer Center we stratify thyroid cancers as low, intermediate, or high risk using GAMES criteria: key prognostic factors include Grade, Age > 45 years old, Metastases, Extrathyroidal extension, and Size > 4 cm.2 Almost 80% of patients fit into the low-risk category, with an overall mortality rate of 1 to 2%. About 20% of patients fit into the high-risk category with a mortality rate of nearly 50%. Thyroid cancer is controversial, because differentiated thyroid malignancies are implicated in the carcinogenesis of the most aggressive human tumor, anaplastic thyroid cancer.
Historically, thyroid surgery, for both benign and malignant disease, was a feared procedure with high mortality rates related to vascular and septic insults. The term “thyroid” (Latin: “shield-shaped”) is attributed to Bartholemeus Eustacius of Rome while Thomas Wharton of London named it “glandular thyroidoeis” in his Adenographia in 1656. In the late eighteenth century, Frederick Ruysch of Leyden suggested that the gland had a secretory role whereas Caleb Hillier Parry of Bath described thyroid function as a vascular reservoir preventing “brain engorgement”. In more recent times, the Nobel Prize winner Theodor Kocher was appointed to the Chair of Surgery in Bern in 1872 and began his landmark surgery with the use of antiseptic techniques, arterial ligation, and precise dissection within the capsule. His progressive understanding of the dangers of capsular trauma rendered the operation less morbid and increasingly oncologic. He initially recorded mortality rates of 13 of 101 procedures, but Kocher also collected data on a further 268 operations performed since 1877, finding that mortality for nonmalignant goiter had fallen to 12% and for malignant goiter to 57%. As more patients survived the surgery, greater insights into the postoperative sequelae were experienced, including recurrent laryngeal nerve injury, myxedema, and tetany. These were identified as serious postoperative complications, encouraging a more cautious resection and a more precise technique by extracapsular dissection. By the time Kocher was awarded the Nobel Prize, with dedicated surgical appraisal and modification, the mortality for a thyroidectomy for simple goiter, in his hands had fallen to less than 1%.3
The parathyroid glands were first discovered in the Indian Rhinoceros by Richard Owen in 1850. It took a further 30 years before Ivar Viktor Sandström (1852–1889), a Swedish medical student, in 1880 identified these organs in humans. It was the last major organ to be recognized in humans.4
The thyroid is a highly vascular gland located anteriorly in the lower neck, extending from the fifth cervical vertebra down to the first thoracic vertebra. The gland is formed by two elongated lateral lobes with superior and inferior poles connected by a median isthmus (with an average height of 12 to 15 mm) overlying the second to fourth tracheal rings. Each lobe is 50 to 60 mm long, with the superior poles diverging laterally at the level of the oblique lines on the laminae of the thyroid cartilage. Thyroid weight varies but averages 25 to 30 g in adults. A conical pyramidal lobe often ascends from the isthmus or the adjacent part of either lobe (more often the left) toward the hyoid bone. The vascularity stems from the superior thyroid artery, which is the first branch of the external carotid artery, the inferior thyroid artery originating from the thyrocervical trunk and occasionally a thyroid ima vessel originating from the aortic arch or brachiocephalic artery. Detailed understanding of the surgical anatomy including anomalous anatomy is necessary for low surgical morbidity.
Lymphatic drainage of the thyroid gland is extensive and flows multidirectionally. The lymphatics are key to thyroid surgery and have obvious implications for oncologic surgery. Four principal lymphatic collecting trunks drain the thyroid. The inferomedial channels drain into the pretracheal and paratracheal lymph nodes (most common route of metastasis). The superomedial channels terminate in the prelaryngeal node (“Delphian node”). The superolateral channels drain into the nodes of the upper internal jugular vein and finally the inferolateral channels extend into the supraclavicular and jugulo-subclavian nodes.
Rouvière described a lymphatic vessel that occurred in one-fifth of the cadaver dissection specimens. This vessel (the posterosuperior collecting trunk) drains the upper pole of the thyroid into the retropharyngeal lymphatic system. Several authors state that the retropharyngeal space communicates with the parapharyngeal space through a dehiscence of the fascia of the superior constrictor muscle. This dehiscence allows metastatic disease to involve the parapharyngeal space.
Parathyroid Glands (Fig 24.1)
The parathyroid glands are four or more small glands located on the posterior surface of the thyroid gland. The parathyroid glands usually weigh between 25 and 40 mg in humans. Occasionally, some individuals may have six parathyroid glands. The parathyroid glands are quite easily recognizable histopathologically from the thyroid, as they have densely packed cells, in contrast with the follicular structure of the thyroid. However, in surgery, they are harder to differentiate from the thyroid or fat and may be devascularized, especially during a central neck dissection for disseminated thyroid cancer.
Recurrent Laryngeal Nerve
The recurrent laryngeal nerve (RLN) innervates the intrinsic laryngeal musculature and supplies sensory innervation to the glottis. The embryology of this nerve begins in its relation to the sixth branchial arch and is associated with the sixth arch arteries. The ventral aspects of the sixth arch arteries become the pulmonary arteries. The dorsal aspects of the sixth arch arteries disappear, allowing the RLN to ascend to the larynx. The fifth arch arteries regress early in development so the RLN is hooked by the fourth arch vessels. The fourth arches on the right and left sides become the subclavian artery and the aortic arch.
Axons of the recurrent laryngeal nerve are grouped within the vagus nerve. As this nerve travels through the skull base via the jugular foramen it lies anterior to the jugular vein. The left vagus nerve follows the carotid artery into the mediastinum crossing the aortic arch anteriorly. The left RLN loops under the aorta medially and ascends the tracheoesophageal groove and is approximately 12 cm from the aorta to the cricothyroid joint. Multiple studies have attempted to document the relationship of the inferior thyroid artery to the RLN.5 The inferior thyroid artery lies anterior to the left RLN in 50 to 55% of patients. The nerve lies anterior to the artery in 11 to 12% of patients. In all remaining patients the nerve rests between the distal arteriolar branches.
The right RLN is a shorter nerve at 5 to 6 cm from the subclavian to the cricothyroid joint. As the right vagus nerve courses along the cowmmon carotid artery, at the division of the innominate artery the right RLN loops around the subclavian artery and travels along the right superior lobe pleura. It enters the tracheoesophageal groove more laterally than the left side behind the common carotid artery. In less than 1% of patients the nerve branches directly from the right vagus at the level of the thyroid gland and is always associated with an anomalous retroesophageal location of the right subclavian artery. The variability of this vessel and its position relative to the RLN make it a poor surgical landmark; however, ligation of the artery should not be performed until the RLN has been correctly identified. At the inferior constrictor muscle the nerve passes deep, posterior to the cricothyroid joint. It is within the larynx where the nerve splits into sensory and motor components. Extralaryngeal division of the RLN is well described and estimated at 35 to 80% of dissections.6 The consistent theme on reports of the course of this nerve is the variability of its anatomical path. Traditional techniques advocate identification of the mid to inferior segment close to the inferior thyroid artery; however, many surgeons search for the distal segment just below Berry′s ligament. This has the advantage of preventing disruption of the blood supply to the inferior parathyroid gland. The only disadvantage of identification of the nerve at the distal segment is the presence of a large tubercle of Zuckerkandl. This tubercle can be classified as grade I, II, and III and can be found in up to 80% of patients undergoing thyroidectomy. Grade I < 0.5 cm, grade II 0.5 to 1.0 cm and grade III > 1 cm. In an otherwise small goiter, a grade III tubercle may be associated with significant compressive symptoms.
The anomalous position of a nonrecurrent laryngeal nerve predisposes the nerve to injury during thyroid surgery and compression by a thyroid mass. A nonrecurrent nerve arises when the fourth arch on the right side disappears and the right subclavian artery arises from the dorsal part of the aortic arch. The right RLN now does not have a recurrent route and directly joins the larynx. There are no convincing reports of a left sided nonrecurrent nerve. Nonrecurrent RLNs are rare but an awareness of their existence and correct surgical technique will prevent the surgeon from iatrogenic trauma if one is encountered.
Thyroidectomy is not an infrequent operation. In the modern era surgical specialization and correct oncologic management demand a more sophisticated approach to thyroid and parathyroid surgery. Anything less may contribute to early tumor recurrence, incorrect therapeutic approach to lateral neck disease, or unnecessary postoperative sequelae. There are definitive data to suggest that low operative volume is associated with a higher incidence of complications. This is true for both surgical trainees and established surgeons.7 Surgical volume also influences the failure pattern after parathyroidectomy for hyperparathyroidism.8 From a technical point of view, the experienced thyroid surgeon is well versed in the normal and aberrant anatomy of the thyroid gland and the necessary maneuvers required preventing complications. More importantly, the surgeon is equipped to identify and deal with unexpected pathology that may require additional procedures such as jugular vein resection, central compartment nodal dissection, or selective lateral compartment nodal dissection. As a tertiary referral center, we often deal with patients who have had suboptimal thyroid surgery, and with issues in reoperative thyroid surgery. Hence, we have made a conscious attempt to reduce the need for secondary thyroid surgery. Shaha9 reported less than 3% incidence of completion thyroidectomy, suggesting that the best and most appropriate treatment decisions are made during the first surgical procedure. This was achieved through careful preoperative and intraoperative assessment of the primary pathology and correct surgical management during the first procedure.
Superior Laryngeal Nerve (Figs. 24.2, 24.3, 24.4)
Injury to the external branch of the superior laryngeal nerve (SLN) is often underestimated, and there are no objective measurements in place to confirm it. Patients usually complain of voice fatigue, inability to shout, scream, or sing. This can be a significant morbidity to professionals, such as singers, whose voice is the basis of their careers. Injury rates have been reported to range from 1 to 5%, but the actual figure is likely to be higher as confirmation of SLN injury may be difficult. Patients at risk include those with high-riding thyroid glands, with a nodule at the upper pole, or large goiters. Direct visualization of the nerve is possible in more than 60% of cases. This, however, places the nerve at unwanted increased risk of injury. When dissecting the prelaryngeal and pretracheal fascia, care should be taken not to injure the cricothyroid muscle, which may be adherent to the thyroid gland.
An improved technique of SLN protection involves downward and lateral traction of the superior pole, which exposes the Joll triangle, the anatomical space between the superior thyroid vessels, superior pole of the thyroid, and cricothyroid muscle. The superior thyroid vessels are then ligated and divided close to the upper pole. This maneuver is effective in preventing SLN injuries in most situations.