Michael Kubala and Brendan C. Stack, Jr.
Abstract
Cervical metastasis in thyroid carcinoma is a common occurrence which needs to be addressed by the head and neck surgeon. This chapter will outline a comprehensive approach to treating neck disease in thyroid carcinoma. Thyroid carcinoma represents approximately 3.4% of all new cancers diagnosed in the United States. Up to 50% of patients with differentiated and 70% with medullary thyroid carcinoma present with nodal disease. In addition to a thorough history and physical examination, ultrasonography with fine needle aspiration of suspicious lymph nodes is the initial choice of imaging to evaluate the central and lateral neck compartments. The current management of thyroid carcinoma is hemi or total thyroidectomy with or without addressing the neck based on characteristics of the primary lesion and lymph nodes status. For differentiated thyroid carcinoma, prophylactic central neck dissection, but not lateral neck dissection, may be advocated for a clinically negative neck in advanced primary cancer. For medullary thyroid carcinoma, prophylactic central neck dissection is recommended in all patients, whereas prophylactic lateral neck dissection is recommended in certain patients. All patients presenting with pathologic cervical disease must have at least a central neck dissection and possible lateral neck dissection if the nodes appear in this compartment. Knowledge of the central and lateral neck compartment is essential to completing any surgical procedure in these areas, communicating in a multidisciplinary team approach to treatment, and minimizing complications.
Keywords: Differentiated thyroid carcinoma, medullary thyroid carcinoma, central neck compartment, central neck dissection, lateral neck compartment, lateral neck dissection
19.1 Introduction
Thyroid carcinoma arises from the thyroid gland, an endocrine organ located in the anterior neck responsible primarily for the regulation of body metabolism. According to Surveillance, Epidemiology, and End Results (SEER) estimates, there will be an estimated 56,870 new cases of thyroid cancer diagnosed in 2017, representing 3.4% of all new cancer cases within the United States. Most new patients are diagnosed during the fifth and sixth decades of life, with a predilection for females and the Caucasian race. The rate of new thyroid cancers has been rising on an average of 3.8% over the past 10 years, seemingly due to increased awareness and detection. Current 5-year survival rates for all comers with thyroid cancer is 98.2%, representing one of the highest survival rates among cancers.1
There are five defined types of thyroid carcinoma: papillary thyroid carcinoma (PTC), follicular thyroid carcinoma (FTC), Hürthle cell (oncocytic), medullary thyroid carcinoma (MTC), and anaplastic. Differentiated thyroid carcinoma (DTC), papillary and follicular, makes up more than 90% of all thyroid cancers. Within DTC, papillary accounts for about 85% of cases.2 PTC is known to spread primarily through the lymphatic system. This usually begins within the first echelon nodes in the central neck compartment (level VI) before spreading to the lateral neck (levels II-IV) or into the superior mediastinum (level VII). FTC, on the other hand, primarily spreads hematogenously with common local invasion of the primary tumor.
It has been established that DTC involves cervical lymph node metastases in 20 to 50% of patients. Cervical lymph node metastasis is a known risk factor for significantly predicted poorer overall survival outcomes.2 MTC is categorized separately from DTC because it develops from a different cell type within the thyroid, the parafollicular C cells. It has been well established that MTC behaves more aggressively than DTC, and therefore, should be treated differently. In the sporadic type of MTC, 70% of patients who present with a palpable thyroid nodule have cervical metastases.3 Because of this high rate of metastases, MTC has a different staging system and recommendations for initial surgical treatment.
The current standard of treatment for all types of thyroid carcinoma is surgical excision in the form of hemi or total thyroidectomy with or without neck dissection at the same time. The need for surgical removal of the lymph nodes of the central and lateral neck, therefore, comes into question during the surgical planning for the treatment of thyroid cancer. Evaluation of the neck for metastases should begin with a cervical ultrasound, preferably at the time of initial diagnosis. Anatomy of the central neck compartment should be completely understood to weigh the risks and benefits of a prophylactic central neck dissection in the clinically negative neck, and to prevent complications during a therapeutic central neck dissection. Lateral neck dissection, commonly done with minimal patient morbidity, should only be done in the presence of confirmed lateral neck pathologic disease.
19.2 Preoperative Evaluation of the Neck for Thyroid Carcinoma
Once the diagnosis of thyroid carcinoma has been established, the neck needs to be evaluated for the presence of locoregional metastasis. The pattern of lymph node metastasis is somewhat predictable for all types of thyroid carcinoma based on location of the tumor within the gland, as seen in Fig. 19.1. Upper third tumors have almost a 3.3 times increased incidence of lateral neck spread (level III/IV) compared to middle or lower third tumors. Likewise, middle third and lower third tumors have about a 3 to 13.5 times increased incidence of central neck spread (level VI/VII) compared to upper third tumors.4 Initial screening of the central and lateral neck compartments of all patients should be done via cervical ultrasound followed by additional imaging studies (usually CT) for advanced, bulky, or invasive disease.2
If, after physical examination and preoperative imaging studies, the patient does not have pathologic appearing lymph nodes, they are classified as a clinically negative neck (cN0). Any lymphadenopathy found should be further investigated. The most common way to diagnose suspicious thyroid nodules and lymph nodes is to perform ultrasound-guided fine needle aspiration (USGFNA). In a high-volume, multispecialty center, FNA can be performed and interpreted by a pathologist during the same clinic visit, expediting the diagnosis, surgical planning, and initiation of treatment. Incisional biopsy is not recommended because this commonly requires entering into or near the thyroid, causing scarring and possibly increasing the difficulty of the subsequent thyroidectomy and/or neck dissection. Once metastasis has been confirmed in either the central or lateral neck, the patient is classified as a clinically positive neck (cN1a or cN1b, respectively).
Fig. 19.1 Lymphatic drainage of the thyroid gland. Superior third tumors have a higher propensity to spread to the lateral neck compared to middle and lower third tumors, which tend to metastasize to the central neck first. (Reproduced from Tang AL, Steward DL. Developmental and surgical anatomy of the thyroid compartment. In: Terris DJ, Duke WS, eds. Thyroid and Parathyroid Diseases: Medical and Surgical Management. New York, NY: Thieme; 2016:11.)
19.2.1 Cervical Ultrasound
Cervical ultrasound of the central and lateral neck should be completed at the time of initial evaluation and FNA of suspected thyroid carcinoma. Preoperative ultrasound identifies suspicious cervical adenopathy in 20 to 31% of cases. Features suspicious for metastatic cancer involvement include enlargement, loss of fatty hilum, round shape, hyperechogenicity, cystic changes, microcalcifications, and increased peripheral vascular- ity.2 No single feature is absolute for malignancy; so, the decision to perform an FNA should be based on the totality of patient risk factors, imaging characteristics, and size greater than 10 mm.
If initial evaluation of an FNA from a lymph node is indeterminate (Bethesda class II), thyroglobulin washout can be completed on the specimen. The addition of thyroglobulin washout is helpful in lymph nodes which are cystic, inadequate, or have indeterminate cytologic evaluation, or inconsistent sonographic characteristics. Currently, studies show that a thyroglobulin level less than 1 ng/mL indicates a benign node.2 No level has been established to indicate malignancy and current research into the ratios of FNA thyroglobulin to serum thyroglobulin may increase predictive accuracy.5
19.2.2 Additional Imaging
The American Thyroid Association (ATA) advocates for the use of cervical ultrasound as the first-line imaging for evaluation of nodal metastasis, followed by cross-sectional imaging such as computed tomography (CT) or magnetic resonance imaging (MRI) if needed. Indications for further imaging would include invasive primary tumor, advanced disease, inability to fully assess nodal extent on ultrasound, posterior location of the thyroid tumor (adjacent to trachea or esophagus), and multiple or bulky lymph node involvement. Invasive disease can be clinically evident with hoarseness, shortness of breath, dysphagia, hemoptysis, or airway obstruction. Findings consistent with laryngeal, tracheal, and/or esophageal involvement will prompt the surgeon to prepare accordingly.
19.2.3 TNM and Staging
The most commonly used staging system for thyroid cancer was developed by the American Joint Committee on Cancer (AJCC). Unlike other cancers of the head and neck, age is an important prognostic factor in this staging system. There are also separate classifications for differentiated, medullary, and anaplastic histologic diagnoses. Table 19.1 and Table 19.2 outline the 7th edition of the AJCC classification for differentiated and medullary thyroid cancer, respectively. Updates to the classification system are expected to take effect in the near future, with the most significant change being increasing the age of poorer prognosis from 45 to 55 years of age. Furthermore, after further studies on survivability, the stages have been shifted down, requiring more advanced disease for higher classification.
19.3 The Central Neck
19.3.1 Surgical Definition of Central Neck Levels
Effective communication of preoperative planning, intraoperative dissection, pathologic reporting, and administration of adjuvant treatment is based on the uniformity of terminology by defining the relevant anatomy of the central neck compartment. Collaboration of multiple surgical societies has led to the definition of the central neck compartment and how it relates to thyroid surgery. The central neck compartment can be defined as levels VI and VII and shown in Fig. 19.2, and includes all of the neurovascular, lymphatic, and visceral components contained within its boundaries.6,7
Table 19.1 American Joint Committee on Cancer TMN Classification for Differentiated and Medullary Thyroid Cancer.
|
Primary tumor (T) |
|
|
TX |
Primary tumor cannot be assessed |
|
T0 |
No evidence of primary tumor |
|
T1 |
Tumor 2 cm or less in greatest dimension limited to the thyroid |
|
• T1a |
Tumor 1 cm or less limited to the thyroid |
|
• T1b |
Tumor between 1 and 2 cm limited to the thyroid |
|
T2 |
Tumor between 2 and 4 cm in greatest dimension limited to the thyroid |
|
T3 |
Tumor greater than 4cm in the greatest dimension limited to the thyroid, or any tumor with minimal extrathyroidal extension (limited to sternothyroid muscle or perithyroidal soft tissue) |
|
T4 |
Advanced disease |
|
• T4a |
Tumor of any size extending beyond the thyroid capsule to invade the soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve |
|
• T4b |
Tumor invades paravertebral fascia or encases carotid artery or mediastinal vessel |
|
Regional lymph nodes (N) |
|
|
NX |
Regional lymph nodes cannot be assessed |
|
N0 |
No regional lymph node metastasis |
|
N1 |
Regional lymph node metastasis |
|
• N1a |
Metastasis to level VI |
|
• N1b |
Metastasis to unilateral, contralateral, or bilateral cervical, retropharyngeal, or superior mediastinal lymph nodes |
|
Distant metastasis (M) |
|
|
M0 |
No distant metastasis |
|
M1 |
Distant metastasis |
|
Source: Data from Edge SB. AJCC Cancer Staging Manual, 7th ed. New York, NY: Springer; 2010. |
|
Table 19.2 American Joint Committee on cancer staging for differentiated and medullary thyroid carcinoma
|
Differentiated thyroid carcinoma |
Medullary thyroid carcinoma |
||
|
Under 45 y old |
|||
|
• Stage I: Any T Any N M0 |
|||
|
• Stage II: Any T Any N M1 |
|||
|
45 y and older |
All ages |
||
|
Stage I |
T1 N0 M0 |
Stage I |
T1 N0 M0 |
|
Stage II |
T2 N0 M0 |
Stage II |
T2-3 N0 M0 |
|
Stage III |
T3 N0 M0 T1-3 N1a M0 |
Stage III |
T1-3 N1a M0 |
|
Stage IVa |
T4a N0-1a M0 T1-4a N1b M0 |
Stage IVa |
T4a N0-1a M0 T1-4a N1b M0 |
Table 19.2 continued
|
Differentiated thyroid carcinoma |
Medullary thyroid carcinoma |
||
|
Stage IVb |
T4b Any N M0 |
Stage IVb |
T4b any N M0 |
|
Stage IVc |
Any T Any N M1 |
Stage IVc |
Any T any N M1 |
|
Source: Data from Edge SB. AJCC Cancer Staging Manual, 7th ed. New York, NY: Springer; 2010. |
|||
Fig. 19.2 Anatomical neck levels. The central neck compartment is defined as levels VI and VII. The lateral neck compartment is defined as levels I through V. (Reproduced with permission from Genden EM, Kao J, Packer SH, Jacobson AS. Carcinoma of unknown primary site. In: Genden EM, Varvares MA, eds. Head and Neck Cancer: An EvidenceBased Team Approach. New York, NY: Thieme; 2008:181.)
Boundaries of the Central Neck
The level VI compartment is bounded superiorly by the inferior border of the hyoid bone, laterally by the medial border of the carotid arteries, anteriorly by the superficial layer of the deep cervical fascia, posteriorly by the deep layer of the deep cervical fascia, and inferiorly by the plane of the sternal notch. The level VII compartment, or anterior superior mediastinal compartment, is bounded superiorly by the plane of the sternal notch, laterally by the mediastinal pleura, anteriorly by the posterior border of the manubrium, posteriorly by the deep layer of the deep cervical fascia, and inferiorly by the innominate artery on the right and corresponding axial plane on the left.7
Lymph Nodes
Within the central neck compartment, the lymph node groups are further defined based on location. The prelaryngeal, or Delphian, nodes are located anterior to the thyroid cartilage and superior to the thyroid gland. The pretracheal nodes are located anterior to the tracheal and between the thyroid gland and the sternal notch. The right and left paratracheal nodal groups are located on either side of the trachea, but have important differences based on the course of their respective recurrent laryngeal nerves (RLNs). In the left paratracheal region, lymphatic tissues generally lie anterior to the RLN. However, since the right RLN courses more ventrally within the paratracheal region because of the innominate artery, lymphatic tissue lies both anterior and posterior to the nerve. Bilaterally, the remaining borders of the paratracheal region are the trachea medially, the common carotid artery laterally, and the retropharyngeal and retroesophageal regions posteriorly.7
Vascular Structures
As described earlier, many vascular structures are present in the central neck compartment. The surgeon needs to be aware not only these vessels but also of their branching vessels. The brachiocephalic, or innominate artery, is the first branch of the arch of the aorta and gives rise to the right subclavian and common carotid arteries. It also determines the more ventral and lateral course of the right RLN. The left common carotid artery is the second branch of the arch of the aorta and defines the left lateral border of the central compartment. The superior thyroid artery is commonly the first branch of the external carotid artery and supplies the superior pole of the ipsilateral thyroid lobe. The inferior thyroid artery is a branch of the thyrocervical trunk from the subclavian artery and supplies the inferior pole of the ipsilateral thyroid lobe. It also supplies the ipsilateral inferior and superior parathyroid glands. The inferior thyroid artery travels posterior to the common carotid artery, but has a highly variable relationship with the RLN.8
The superior and middle thyroid veins drain into the internal jugular vein. The superior vein accompanies its paired artery; however, the middle vein does not have a paired artery. The inferior thyroid veins are variable in number and location, draining most commonly into the brachiocephalic veins, and also into the internal jugular vein. Although the internal jugular vein does not by definition lie in the central neck compartment, it is worth noting that its intimate association with the common carotid artery can bring it into the surgical field if tissue is dissected and retracted into the surgical field.
Nerves
Several nerves lie within the central neck compartment and have significant clinical importance. The RLN is a branch of the tenth cranial nerve (Vagus) and is derived from the sixth branchial arch. It innervates all of the intrinsic muscles of the larynx with the exception of the cricothyroid muscle and provides sensation to the larynx below the glottis, along with portions of the trachea and esophagus. During embryologic development, the RLN courses around the arteries of the sixth branchial arch. On the left, this is the ductus arteriosus, which ex utero becomes the ligamentum arteriosum. On the right, the sixth branchial artery is obliterated. The RLN then migrates cranial to the next remaining branchial artery, the right subclavian artery. Therefore, the course of the RLN varies between the right and left sides of the body.
The right subclavian artery lies more anterior and lateral compared to the aortic arch and ligamentum arteriosum on the left. This results in the nerve traveling more lateral to medial and anterior to posterior on the right when it comes back to the larynx, as opposed to simply traveling superior in the tracheoesophageal groove as it on the left. The motor fibers of the nerve enter the larynx posterior to the cricothyroid joint underneath the inferior constrictor muscle.
Although rare, the head and neck surgeon must be aware of the possibility of a non-RLN (NRLN). This anomaly occurs almost exclusively on the right, with a prevalence of 0.7% in the general population. The most common cause of an NRLN is failure of the embryologic development of the right fourth branchial arch, the subclavian artery. It has been found that 86.7% of right NRLNs are associated with an aberrant subclavian artery pattern. These nerves can originate either above or below the laryngotracheal junction and track with the superior thyroid artery, branch directly off the Vagus, or display a looping trajectory into the laryngotracheal junction.9
The external branch of the superior laryngeal nerve (EBSLN) branches from the Vagus nerve high in the neck and accompanies the superior thyroid vasculature as it courses toward the cricothyroid muscle. It inserts directly into the muscles, which acts as a laryngeal tensor. Classification schemes have been proposed to describe the location of the EBSLN for better identification and preservation during thyroid or central neck dissection. They focus on several aspects of the nerve’s course, including the intersection with the superior thyroid vessels, location on the nerve above a horizontal plane of the superior border of the superior thyroid pole, location of the cricothyroid-inferior constriction junction, and distance between the nerve and the superior thyroid vessels.10,11.12.13.14 Complete discussion of these schemes is beyond the scope of this chapter.
Parathyroid Glands
The parathyroid glands are endocrine glands located on the posterior aspect of the thyroid gland and secrete parathyroid hormone, which regulates calcium homeostasis in the circulation. The inferior parathyroid glands migrate caudally in the anterior neck in association with the thymus gland. The final location of the inferior parathyroid glands is wherever the glands separate from the thymus. This can be anywhere from the hyoid bone to the lower mediastinum. In approximately 50% of patients, the inferior parathyroid glands can be found within 1 cm inferior, lateral, or posterior to the inferior pole of the thyroid. They are located typically anterior to the coronal plane drawn along the vertical axis of the RLN.
The superior parathyroid glands migrate attached to the posterior midportion of the thyroid lobe and, therefore, have a more predictable location in the central neck. In 85% of cases, the superior gland may be located on the posterior aspect of the thyroid lobe in a 2-cm diameter circle centered 1 cm above the crossing of the inferior thyroid artery and the RLN. The superior parathyroid glands lie posterior to the coronal plane drawn along the RLN.15
19.3.2 Central Neck Dissection
In patients diagnosed with PTC, 35% present with clinically evident regional nodal metastasis. Furthermore, up to 80% of patients presenting with no clinical evidence of nodal disease will have microscopic evidence of metastasis following elective neck dissection.16 Zhang et al found in a retrospective study of more than 1,000 patients that male gender, age younger than 45 years, multifocal lesions, extrathyroidal extension, and primary tumors greater than 6 mm were risk factors for central neck metastasis.4
Uniformity in the reporting of nodal regions dissected, the surgical procedure performed, and the exact location of disease is crucial for the complete treatment of thyroid carcinoma. The American Head and Neck Society Endocrine Committee recently published guidelines for reporting central neck dissections. The procedure should be defined as either prophylactic (elective) or therapeutic. Distinguishing the differences between these two categories is important for the preoperative counseling of the patient. For prophylactic neck dissections, the surgeon must explain the risk, benefits, and alternatives to patients as well as why, if they have no apparent disease within the lymph nodes, he or she would advise for the removal of the lymph nodes.
Defining the extent of the central neck dissection is important for staging, adjuvant treatment, and, if necessary, revision operations. The term “central neck dissection” implies the surgeon removed the entire contents of the pretracheal and prelaryngeal lymph nodes, which is rarely the case in practice. The designation of the procedure is completed by including laterality or bilateral. By including right, left, or bilateral, the surgeon indicates removing the paratracheal lymph nodes on that respective side. Therefore, a complete description of a central neck dissection should be [prophylactic/therapeutic] [right/left/ bilateral] central neck dissection.16
Complete dissection and removal of compartmental lymph nodes provide the best initial surgical management of disease. Previous methods of “berry picking,” or choosing pathologic appearing lymph nodes intraoperatively, can miss microscopic disease within the remaining lymph nodes. It can also lead to increased complications from inadequate dissection of critical structures. Therefore, berry picking lymph nodes is not recommended for central neck dissections.16
19.3.3 Prophylactic Central Neck Dissection
A thorough discussion must take place between the patient and the multidisciplinary team before proceeding with a prophylactic neck dissection in a cN0 neck. The goals of the procedure are to improve disease-free survival, decrease the risk of local recurrence, improve the accuracy of posttreatment thyroglobulin level, determine the need for postoperative radioactive iodine therapy, and guide the long-term management of disease. Best evidence for determining the need for prophylactic central neck dissection in the cN0 neck would be a prospective, randomized control trial; however, one does not currently exist in the literature.
The ATA addressed the issue of neck dissections in the 2015 American Thyroid Association Guidelines Task Force on Thyroid
Nodules and Differentiated Thyroid cancer. From this, they developed guidelines for prophylactic central neck dissections. Since approximately 14% of T1 DTC patients present with central compartment metastasis, prophylactic central neck dissection is not recommended in carcinomas less than 2 cm without extrathyroidal extension without clinical or sonographic lym- phadenopathy.2 No improvement was shown in long-term patient outcome, while increasing the likelihood of temporary morbidity.
Prophylactic central neck dissection should be offered to patients who have advanced (T3/4) primary tumors or clinically involved lateral compartment neck nodes, that is, clinical metastases that skip level VI. In patients with T4 cancer, approximately 86 and 93% will have metastasis to the central and lateral compartments, respectively.2 Prophylactic neck dissection is also advocated in patients who show aggressive disease characteristics, such as older or very young age, multifocal disease, or aggressive pathologic variants (tall cell, diffuse sclerosing, insular variants). The current evidence also shows that the presence or absence of molecular markers are not independent prognostic indicators of survival, and should therefore not be considered when deciding to undergo a prophylactic neck dissection.16
The management of prophylactic central neck dissection is somewhat different in children, seemingly due to two specific factors. First, the vast majority of children present with some form of regional lymph node metastasis. Second, decreased disease-free survival is most strongly correlated with the presence of persistent or recurrent locoregional disease. Extent of dissection is based on consideration of focality, size, and experience of surgeon as compared to the risks of the procedure. Ipsilateral dissection should occur for ipsilateral thyroid disease, and contralateral dissection can be based on size and intraoperative findings.17
Management of the central neck in MTC tends to be more aggressive when compared to DTC. Overall metastasis of MTC to the central or lateral neck compartments can be greater than 75%. Disease spread to the ipsilateral central and lateral neck is approximately 80% and spread to the contralateral neck is approximately 45%. Because of the significant tendency for MTC to spread to adjacent neck lymph nodes, all patients with diagnosed MTC with a cN0 neck may be considered for a bilateral central neck dissection.18
19.3.4 Therapeutic Central Neck Dissection
A therapeutic central neck dissection should be performed in any patient who presents with clinically apparent central compartment lymphadenopathy on physical examination or imaging. This should be performed at the same time as total thyroidectomy, since dissection of the central neck after thyroidectomy will have the added challenge of scarring and destruction of tissue planes.2 The recommendation for therapeutic central neck dissection also applies to children with proven gross extrathyroidal and/or locoregional metastasis.17
The extent of therapeutic neck dissection needs to address the distribution of disease while taking into account the risks of bilateral central compartment surgery. If central neck lym- phadenopathy is unilateral on preoperative evaluation, the ipsilateral paratracheal lymph nodes should be removed. The patient should also be informed of the possibility of contralateral paratracheal dissection based on intraoperative examination of lymph nodes.16
Bilateral therapeutic central neck dissection should be recommended to patients with bilateral central neck lymphaden- opathy on initial presentation. Bilateral dissection for unilateral central neck disease remains an area of controversy with need for further research. Currently, it has been noted that bilateral dissection may be associated with higher morbidity, primarily RLN palsy, and hypoparathyroidism, with no reduction in the rate of recurrence. Therefore, the decision to proceed with contralateral dissection for single-sided disease should be based on pathologic characteristics of the initial biopsy, intraoperative findings, and patient risk factors as described previously.16 Any patient with MTC who presents with positive central neck nodes should undergo a bilateral central neck dissection.18
19.3.5 Central Neck Complications
As with any surgical procedures, there exists risks to the anatomical structures of the surgical field that can result in morbidity and possibly mortality to the patient. Mortality from central neck dissection is extremely rare; however, morbidity, including hypoparathyroidism, injury to the RLN, or injury to the external branch of the superior laryngeal nerve, is not uncommon. These morbidities are most commonly transient, but permanent adverse consequences are certainly a reality after a central neck dissection. The most significant possible morbidity would be the need to place a tracheotomy tube.
Hypoparathyroidism
Transient or permanent hypoparathyroidism is a common morbidity following central neck dissection caused by either the direct removal of parathyroid tissue or devitalization of parathyroid tissue in situ. Hypoparathyroidism leads to hypocalcemia causing symptoms such as numbness or tingling around the mouth or in the fingers and toes, muscle cramps, carpopedal spasm, fatigue, irritability, altered mental status, or abnormal ECG findings. Permanent hypoparathyroidism is defined as requiring therapeutic vitamin D and/or calcium replacement at 6 months postoperatively or a fasting albumin- corrected serum calcium below 8.0mg/dL. Incidental parathyroidectomy during central neck dissection for thyroid carcinoma has been found to be between 28 and 41%.19.20 Central neck dissection in the setting of total thyroidectomy is an independent risk factor for incidental parathyroidectomy with an odds ratio of 9.6.20 The overall rate of transient and permanent hypoparathyroidism in central neck dissection for thyroid carcinoma is difficult to determine due to variations between prophylactic and therapeutic dissections, ipsilateral and bilateral dissections, and dissections done with or without concurrent thyroidectomy. Transient hypoparathyroidism ranges from 9 to 52%, whereas permanent hypoparathyroidism ranges from 2.6 to 16.2%.21,22,23
Dissection of the parathyroid glands should proceed in an atraumatic manner with preservation of the blood supply from the inferior thyroid artery. The superior parathyroid glands are more easily identified and dissected from the surgical specimen based on their more reliable location posterior to the superior pole of the thyroid gland. Consequently, the superior glands are most likely preserved during central neck dissection. The locations for the inferior parathyroid glands within the central neck are more variable, which put them at higher risk for incidental parathyroidectomy during dissection.24 If the parathyroid glands are not identified and preserved in situ, the surgical specimen should be examined for potential parathyroid candidates. Biopsy and frozen specimen are used to confirm parathyroid tissue, and not tumor or thyroid tissue, before autotransplantation is performed. The resected parathyroid tissue should be minced into small 1- to 2-mm pieces and inserted into an ipsilateral strap or sternocleidomastoid muscle. Routine autotransplantation of the inferior parathyroid glands has been shown to reduce the rate of permanent hypoparathyroidism if the gland was devascularized or if incidental parathyroidectomy occurred.25
Unilateral Recurrent Laryngeal Nerve Injury
Damage to the RLN is arguably the most feared complication during thyroidectomy or central neck dissection. The RLN innervates the intrinsic muscles of the larynx, including the only abductor muscle, the posterior cricoarytenoid muscle. Transient or permanent injury to the nerve can result in dysfunction of the ipsilateral side of the larynx with limited or no mobility of the vocal cord. This can cause considerable morbidity to the patient, including hoarseness, shortness of breath, activity intolerance, and aspiration leading to pneumonia. Transient nerve injury is commonly defined as evidence of nerve dysfunction from the immediate postoperative period to 6 months. Permanent nerve injury is diagnosed once dysfunction has persisted for 6 months, with a definitive diagnosis at 1 year.
Jeannon et al did a systematic review of more than 25,000 patients undergoing thyroid surgery to determine the incidence of RLN injury. They found a 9.3% incidence of temporary injury and a 2.3% incidence of permanent injury. Furthermore, they investigated the most common methods to evaluate the larynx, including indirect laryngoscopy, fiberoptic nasolaryngoscopy, and video stroboscopy. Although videostroboscopy evaluation discovered the lowest incidence of nerve palsy, it requires specialized equipment that may not be available in all offices. Therefore, they recommended that patients presenting with postoperative symptoms of RLN palsy be evaluated with fiberoptic nasolaryngoscopy.26
Extralaryngeal branching (ELB) of the RLN is a known risk to the nerve during dissection. A systematic review of more than 28,000 nerves found the prevalence of ELB to be 60%. Interestingly, the prevalence was 73% in cadaveric studies and only 39% in intraoperative studies, suggesting that ELB is significantly underreported from the operating room since it is not routinely examined. There are several patterns of branching, with bifurcation being the most common and branching occurring within 2 cm of the cricothyroid joint. When branching occurs, it is almost certain that the anterior branch will have positive motor response.27 The presence of ELB has been found to increase unilateral temporary nerve palsy approximately 7 times and permanent nerve palsy 13 times compared to nonbranching nerves.28 Therefore, it is imperative that the surgeon be aware of possible branching of the nerve during identification.
The traditional method to prevent damage to the RLN is through meticulous dissection and preservation. However, even the most minute trauma to the nerve can result in clinical symptoms. In order to decrease the likelihood of nerve trauma, intraoperative nerve monitoring (IONM) has been developed to aid in the identification of the RLN. IONM consists of electrophysiological measurements of the intrinsic muscle of the larynx by electrodes on specialized endotracheal tubes. Responses to stimulus of the nerve before and after removal of the thyroid gland and central neck contents can theoretically predict potential nerve palsy. Use of IONM can aid in the identification of the RLN in between 98 and 100% of cases.16 IONM has not become a universal standard in all cases, as a systematic meta-analysis comparing visualization alone to IONM found no statistical significance in RLN palsy in all cases.29 However, there does seem to be an advantage of using IONM for high-risk, reoperative, complex, or bilateral thyroid surgery.2 Unfortunately, difficult RLN dissections cannot always be anticipated, and argument exists for universal monitoring. In the unlikely scenario of nerve transection, primary reanastomosis is strongly recommended.
Bilateral Recurrent Laryngeal Nerve Injury
This very rare, but extremely serious, complication occurs as a result of injury to the bilateral RLNs during either total thyroidectomy or bilateral central neck dissection. The vocal cords will become fixed in the median, paramedian, or lateral position in the glottis, resulting in a varying degree of airway obstruction. It is difficult to determine the exact incidence of this complication due to its rarity, but estimates of permanent paralysis range from 0.01 to 0.6%.30
Injury to the External Branch of the Superior Laryngeal Nerve
Injury to the external branch of the superior laryngeal nerve will cause ipsilateral paresis or paralysis to the cricothyroid muscle. Clinically, this can result in a spectrum of voice changes such as a hoarse/breathing voice, vocal fatigue and diminished vocal performance (especially in high pitch and singing voices), decreased loudness, and vocal fatigue. The rate of EBSLN injury varies between 0 and 58% seemingly due to limited data, variability of vocal symptoms, and difficulty identifying changes in postoperative laryngoscopic exams.31 As with the RLN, IONM has become more common with the external branch of the superior laryngeal nerve. Several studies have shown that the use of IONM identifies the EBSLN in up to 98.5% of cases, which can decrease the rate of nerve injury during dissection.14
19.4 The Lateral Neck
19.4.1 Surgical Definitions of Lateral Neck Levels
Starting from the radical neck dissections in the early 20th century to the selective neck dissections of the modern era, the classification of surgical lymph node groups in the lateral neck have developed as a way to better understand head and neck cancer. The ATA has developed a consensus statement for lateral neck dissection anatomy, terminology, and rationale to better facilitate treatment of thyroid carcinoma.32 The lateral neck is defined by levels II, III, IV, and V in Fig. 19.2.
Boundaries of the Lateral Neck
This is reviewed here for thyroid nodal disease, but is addressed in greater detail in Chapter 2. Level I, otherwise known as the submandibular and submental nodal groups, is defined by the body of the mandible superiorly, stylohyoid muscle posteriorly, and the digastric muscle anteriorly and posteriorly. This level is further subdivided into Ia and Ib. The submental nodal group, Ia, does not carry a laterality and is bounded by the anterior bellies of the digastric muscles and the hyoid bone. The submandibular nodal group, Ib, is bounded by the anterior and posterior bellies of the ipsilateral digastric muscle along with the mandible. It also contains the submandibular gland.
Level II, the upper jugular nodal group, extends from the skull base inferiorly to the inferior border of the hyoid bone. The anterior border is the stylohyoid muscle, and the posterior border is the posterior border of the sternocleidomastoid muscle. The deep border is the fascia overlying the levator scapulae muscle. The spinal accessory nerve traverses obliquely in an anterosu- perior to inferolateral fashion to divide this level into IIa, the anteroinferior contents, and IIb, the posterosuperior contents.
Level III, the midjugular nodal group, lies between the lower border of the hyoid bone and a horizontal plane from the lower border of the cricoid cartilage. The anterior border is the sternohyoid muscle, and the posterior border is the posterior border of the sternocleidomastoid muscle. The deep border is the deep cervical fascia overlying the anterior scalene muscle.
Level IV, the lower jugular nodal group, lies between the lower border of the cricoid cartilage and the superior border of the clavicle. The anterior and posterior borders are the same as level III. The deep border is the fascia overlying the cervical plexus. The thoracic duct, the largest vessel of the lymphatic system, is most commonly found near the junction of the left internal jugular subclavian veins. A systematic review of scientific literature determined that the thoracic duct most commonly enters the internal jugular vein (46%), followed by the jugulo-venous angle (32%), and the subclavian vein (18%). Other sites of termination include the external jugular vein, brachiocephalic vein, transverse cervical vein, suprascapular vein, and a right-side termination.33 It is important to know that the thoracic duct lies superficial to the fascia of the anterior scalene muscle, putting it at risk during dissection of the inferior portion of level IV.
Level V, the posterior neck triangle, has its apex at the convergence of the sternocleidomastoid and the trapezius muscle, and base at the superior border of the clavicle. The anterior border is the posterior border of the sternocleidomastoid. The posterior border is the anterior border of the trapezius. This level is subdivided by a horizontal plane continuous with the inferior border of the cricoid cartilage. Superiorly is Va, containing the nodes around the spinal accessory, and inferiorly is Vb, containing the transverse cervical and supraclavicular nodes.
Vascular Structures
The lingual artery, the second branch of the external carotid artery, is present briefly in level I deep to the submandibular gland before running deep to the hypoglossal muscle. The facial artery branches off the external carotid artery posterior to the posterior belly of the digastric muscle. It runs on the deep surface of the submandibular gland before emerging near the inferior border of the mandible deep to the marginal mandibular nerve. The Hayes Martin Maneuver can be performed to protect the marginal mandibular nerve by ligating the facial pedicle at the inferior margin of the mandible and reflecting the soft tissue, along with the nerve, superiorly out of the surgical field. The submental artery branches from the facial artery deep to the submandibular gland and runs anteriorly superficial to the mylohyoid muscle. The facial vein originates in the lower portion of the face, joining the facial artery, as it crosses superficial to the inferior border of the mandible. Unlike the facial artery, the facial vein runs superficial to the submandibular gland before joining the anterior division of the retromandibular vein to form to common facial vein, which then drains into the internal jugular vein.
Few arterial structures are present in levels II, III, and IV. The occipital artery, a branch of the external carotid artery, may be encountered in the superior portion of level IIb as it crosses superficial to the internal jugular vein and cranial nerve XI. Here, it will branch to supply the superior portion of the sternocleidomastoid muscle. The inferior thyroid artery, from the thyrocervical trunk, is present in level IV and courses medially deep to the common carotid artery on its way to the inferior pole of the thyroid gland. The common, internal, and external carotid arteries are found at the medial boundary spanning the lateral neck, and, as a general rule, should be minimally manipulated during dissection unless there is gross involvement by primary or metastatic disease.
The internal jugular vein is present at the medial aspect of levels II to IV, beginning at the skull base, deep to the posterior belly of the digastric muscle, and terminating in the brachiocephalic vein after joining with the subclavian vein. The vein does not typically have lateral branches. The thyrolinguofacial trunk arises medially from the internal jugular vein and will be encountered as the jugular lymph nodes are dissected off the vein.
Arteries encountered within level V include the first part of the subclavian artery, giving rise to the thyrocervical trunk and then to the transverse cervical artery. The transverse cervical artery courses in a medial to lateral fashion superficial to the anterior scalene muscle but deep to the omohyoid muscle before it divides into its superficial and deep branch at the anterior border of the trapezius. The external jugular vein is formed from the confluence of the posterior division of the retromandibular vein and the posterior auricular vein. It crosses superficially to the sternocleidomastoid muscle to empty into the subclavian vein within level V.
Nerves
Several cranial nerves, nerves of the cervical plexus, the brachial plexus, and the sympathetic cervical chain are found in multiple levels within the lateral neck compartment. The marginal mandibular branch of cranial nerve VII exits the parotid gland in the lower lateral part of the face and crosses the mandible twice before innervating the nerves of the lower lip and chin. The lower extent of the nerve is commonly 1 to 2 cm below the angle of the mandible within level I. The lingual nerve is a sensory nerve from the mandibular division of the trigeminal nerve which provides sensation and taste to the anterior two-thirds of the tongue. It is found during removal of the submandibular gland, when the mylohyoid is reflected to expose the lingual nerve superficial to the submandibular duct.
Cranial nerve X, the vagus nerve, contains sensory, motor, and autonomic branches innervating multiple areas of the body. Regarding the head and neck, it provides sensation and motor control of skeletal muscles to the pharynx and the larynx via the superior and RLNs. Traveling through the neck in the carotid sheath between the internal jugular vein and carotid arteries, it is present in levels II to IV and should not be extensively manipulated during routine lateral neck dissection.
Cranial nerve XI, the spinal accessory nerve, is a motor nerve innervating the sternocleidomastoid and trapezius muscles. It travels in a mediolateral and superoinferior direction from the jugular foramen, anterior to the vagus nerve, to the sternocleidomastoid muscle, dividing level II into two sections. After piercing the sternocleidomastoid muscle, it continues through level V to enter the trapezius. The two muscles combined to help tilt and rotate the head, elevate the shoulder, and abduct the arm.
Cranial nerve XII, the hypoglossal nerve, is a motor nerve innervating the extrinsic, except for the palatoglossal, and intrinsic muscles of the tongue. After it leaves the skull base through the hypoglossal canal, the nerve passes between the internal jugular vein and the carotid arteries as it arches toward the tongue. It reaches the posterior aspect of the greater cornu of the hyoid bone before traveling anteriorly deep to the submandibular duct. Therefore, its importance is the dissection of levels I and II.
The cervical plexus is a syncytium of the anterior rami of the first four cervical spinal nerves. It gives rise to the ansa cervica- lis, the greater auricular nerve, and the phrenic nerve. The ansa cervicalis, arising from C1 to C3, provides motor control to the strap muscles, except for the thyrohyoid, and sits superficial to the carotid sheath. The greater auricular is formed from C2 and C3, providing sensation to the skin overlying the parotid gland and the ear lobule. It courses around the posterior border of the sternocleidomastoid muscle as it travels superiorly toward the parotid gland. It is often encountered while defining the lateral border of level II. The phrenic nerve is both a sensory and motor nerve to the diaphragm formed from C3 to C5. It lies deep to the prevertebral layer of the deep cervical fascia over the anterior scalene muscle deep to level IV.
The second neurologic plexus of the neck is the brachial plexus. It is formed by the anastomoses of anterior rami of the spinal nerves C5 to C8 and T1. It provides both sensory and motor control to the chest and ipsilateral upper extremity. It is found within level V in the fascia between the anterior and medial scalene muscles.
The cervical sympathetic chain is part of the sympathetic nervous system providing vasoconstrictive innervation to involuntary smooth muscles of the head and neck along with secretory control to the lacrimal and salivary glands. It is located within the deep portion of the prevertebral fascia anterior to the transverse process of the vertebral bodies. The cervical sympathetic chain commonly consists of three ganglia: the superior, middle, and inferior (stellate). The superior ganglion is consistently located near the skull base at the opening of the carotid canal. The middle ganglion lies near the inferior thyroid artery. The inferior ganglion is typically fused with the first thoracic ganglion to form the stellate ganglion just posterior to the origin of the vertebral artery.
19.4.2 Lateral Neck Dissection
As with the central neck dissection, having a uniform system to describe the extent of a lateral neck dissection is essential to operative planning, pathologic reporting, and arranging adjuvant therapy.6,32 The terms radical and modified radical neck dissections are inadequate to describe the extent of a dissection in the modern era. Selective neck dissection has become the most widely accepted terminology and refers to the removal of less than all five nodal levels with the preservation of the spinal accessory nerve, internal jugular vein, and sternocleidomastoid muscle. The procedure should be reported with the side and level/sublevels dissected.32
Lateral neck dissection for DTC is dependent on the most common pathways of nodal drainage. Risk factors for spread to the lateral neck include extrathyroidal extension, multifocal lesions, and central neck disease.4 It has been shown that skip metastasis to the lateral neck compartment can occur in up to 18% of papillary thyroid carcinoma.16 Skip metastasis is defined as spread of metastatic disease past the first echelon nodes of the central neck to the second echelon nodes of the lateral neck (VI or III). The ATA advocates that a routine selective lateral neck dissection for thyroid carcinoma should include levels IIa, III, IV, and Vb. Dissection in level IIb is undertaken only if there is preoperative evidence of disease in this level or suspicious appearing nodes in upper level IIa which lie in close proximity to IIb. This also applies to level Va, which should only be explored with preoperative evidence of suspicious lymphadenopathy.2
MTC tends to have about the same chance of skip metastasis when compared to DTC, about 25%. Furthermore, the rate of lateral neck metastasis tends to be directly related to the frequency of central neck spread.18 In patients with minimal central neck disease, the rate of ipsilateral and contralateral lateral neck disease was found to be 77 and 38%, respectively. The same study found that advanced central neck disease had a 98% chance of ipsilateral and 77% chance of contralateral lateral neck disease.34 Preoperative serum calcitonin also has a predictive value for the extent of metastatic spread, with increasing levels indicating more distant spread with a less likely chance of a biochemical cure.18
19.4.3 Prophylactic Lateral Neck Dissection
When considering a lateral neck dissection in a patient with DTC and a cN0, the surgeon must consider the possible rate of metastasis and the potential morbidity of the procedure. As determined by the ATA and supported by the American Head and Neck Society, prophylactic neck dissection is not considered appropriate in any DTC patient with a clinically negative neck. This is also true for children.2,17
As previously described, the rate of metastasis in MTC is higher when compared to DTC and can be directly related to the serum calcitonin level. It has been advocated that a serum calcitonin level of greater than 20 pg/mL be used as a cutoff to proceed with a prophylactic lateral neck dissection in cN0.18 No consensus was made for this number, and further investigations are needed to support this decision. Prophylactic contralateral lateral neck dissection is recommended in patients with serum calcitonin levels of greater than 200 pg/mL, central compartment disease, and positive preoperative imaging of the ipsilateral lateral neck com- partment.18
19.4.4 Therapeutic Lateral Neck Dissection
For DTC and MTC, therapeutic lateral neck dissection should only be performed for biopsy-proven metastasis in levels II to V. When metastasis is present on the initial presentation, lateral neck dissection should take place at the same time as total thy- roidectomy.2
Metastasis or recurrence of disease may occur several years or even decades after initial presentation. Surveillance of the lateral neck with ultrasound should occur every 6 to 12 months after completion of initial treatment, depending on the risk category of the patient. If suspicious lymph nodes appear as described previously, they should be biopsied and treated with lateral neck dissection if pathologic.32
Preoperative confirmation of recurrent disease can be achieved with a second set of imaging, typically a CT scan of the neck with contrast. However, localization of disease intraoperatively in a previous surgical field can be difficult because of scar tissue. Ra- dioguided surgery has been shown to be effective for localization in other head and neck procedures, such as parathyroidectomy and sentinel lymph node biopsy. First developed after using residual therapeutic radioactive iodine 131, radioguided surgery using 99m-technetium, 18F-fluorodeoxyglucose, or 131-iodine is useful and can be a valuable tool for recurrent PTC.35,36,37
Therapeutic lateral neck dissection in children should be performed only after cytologic confirmation of metastasis. As with adults, this should proceed in a compartment-oriented fashion, typically consisting of levels II, III, IV, and Vb. There has been no evidence to support contralateral dissection without proven disease.17
19.4.5 Lateral Neck Complications
Marginal Mandibular Nerve
Injury to the marginal mandibular nerve can occur during level Ib and high level IIa neck dissections. As described earlier, the nerve can be found within the fascia superficial to the facial pedicle along the inferior border of the mandible. Reflecting the fascia out of the surgical plane after ligation of the pedicle can theoretically protect the nerve during dissection. Insult to the marginal mandibular nerve will cause weakness or paralysis to the depressor labii inferioris, depressor anguli oris, and mentalis muscles, resulting in an asymmetric smile and oral incompetency particularly with liquids. The incidence rates of temporary paresis and permanent paralysis have been found to be 14% and 4 to 7%, respectively, following level I neck dissection. However, the same study found that dissection of level IIa without level Ib resulted in no cases of marginal mandibular nerve weakness.38
Spinal Accessory Nerve
Injury or sacrifice of the spinal accessory nerve will lead to the painful and debilitating shoulder syndrome. Patients will often present with excruciating pain (anesthesia, neuropathic pain) to the neck, upper back, and affected shoulder. The paralyzed sternocleidomastoid and trapezius will cause limited abduction of the arm, shoulder droop, scapular winging, and internal rotation of the arm. Much of our knowledge of the shoulder syndrome comes from the morbidity of treating head and neck squamous cell cancer in the past with radical neck dissections. Over time, with further studies into the drainage patterns of head and neck cancers and the survivability after neck dissection, modifications to the radical neck dissection were made to spare the spinal accessory nerve. In the current era of treatment, intentional resection of the spinal accessory nerve is only indicated with gross tumor involvement of the nerve found intraoperatively or inability to remove the tumor without removing the nerve. Injury to the spinal accessory nerve is relatively uncommon, with transient and permanent paresis estimated to be about 1 and 0.3%, respectively.39 Treatment of spinal accessory deficit is primarily physical therapy focused on strengthening the surrounding muscles to compensate for the deficiencies.
Hypoglossal Nerve
The hypoglossal nerve is the sole innervating nerve for the extrinsic and intrinsic muscles of the tongue, except for the palatoglossus. Therefore, damage to the nerve during dissection of level Ib or IIa can lead to weakness and atrophy of one side of the tongue affecting speech and the oral phase of swallowing. Iatrogenic injury has been estimated to be less than 1% in lateral neck dissections for thyroid cancer.39
Brachial Plexus
Injury to the brachial plexus during lateral neck dissection is a rare occurrence, with only a handful of case reports published. Most involve an anatomic variant of the superior trunk, C5 and C6, traveling over the supraclavicular fat pad before diving posteriorly behind the clavicle. Injury to the superior root will cause an Erb-Duchenne palsy with the arm rotated medially by the patient’s side and the forearm in an extended and pronated position.40,41 There have been no reported cases of injury to the middle or inferior trunk. The anterior scalene muscle covers these trunks of the brachial plexus, making injury to these extremely difficult without any reported cases.
Cervical Sympathetic Chain
Damage to the cervical sympathetic chain is an extremely rare complication of neck dissections, reported as less than 1% of all neck dissections.42 No literature has been published examining the incidence of this complication specifically in lateral neck dissection for thyroid carcinoma. Most common situations which put the cervical sympathetic chain at risk during dissection are inadvertent dissection beyond the carotid sheath into the prevertebral fascia and tumor and/or metastatic extensive into the prevertebral space. Injury to the chain will result in Horner’s syndrome, resulting in ipsilateral eyelid ptosis, miosis with anisocoria, facial anhydrosis, and enophthalmos.
Cervical Plexus
The location of the great auricular nerve puts it at risk during level II dissection primarily in two situations. First, the nerve can be easily transected during the raising of skin flaps because of its superficial location lateral to the border of the platysma in the subcutaneous tissue. Secondly, the nerve commonly runs through the superior aspect of level II, limiting or obstructing the removal of tissue from IIb. Sacrifice of the nerve may be necessary in order for the dissection to be completed in its entirety. Dysesthesia can occur as a result of injury to the great auricular nerve, with patients describing the sensation of burning, itching, electrical shock, or pins and needles to the skin overlying the parotid gland and ear lobule. Shaving, talking on the phone, and putting in earrings can turn from an everyday process to a painful activity. Many patients experience recovery of the majority of their anesthesia 9 to 12 months postoperatively. Studies on the incidence of great auricular nerve injury after neck dissection are lacking and could be determined with further research.
The phrenic nerve lies underneath the prevertebral fascia of the deep cervical plexus and is not encountered during lateral neck dissection unless the surgeon goes beyond the boundaries of level IV. Injury to the phrenic nerve can result in elevation of the ipsilateral hemidiaphragm causing reduction in lung capacity, shortness of breath, and fatigue. Polistena et al found an incidence of 0.14% injury to the phrenic nerve in a retrospective institutional review of 675 lateral neck dissections for thyroid cancer. This occurred in a patient with direct metastatic infiltration of tumor into the nerve.39
Chyle Leak
Chyle leak, or chyle fistula, occurs when there is damage to the thoracic duct or lymphatic vessels leading to the accumulation of lymphatic fluid within the surgical bed. The location of the thoracic duct is highly variable not only in its terminal location but also in the path which it takes to get there, making it highly susceptible to injury. Incidence of chyle leak during lateral neck dissection for thyroid cancer is between 1 and 8%.43 A prospective study for the identification of chyle leak during lateral neck dissection found an intraoperative leak rate of 5.2%, all of which occurred on the left side. Interestingly, the same study had a postoperative chyle leak rate of 8.3%, with 62.5% of those occurring in the right neck.44 Therefore, it is pertinent for the surgeon to be diligent within the right neck during dissection, as careless dissection can lead to transection of an aberrant thoracic duct or large lymphatic duct. An extremely rare, but potentially major, complication involving the thoracic duct is a chylothorax, or accumulation of chyle within the pleural cavity. A systematic review of the literature calculated the incidence of chylothorax in thyroidectomy with neck dissection to be 1.85%, with 20 total cases reported.45
Vascular Injury
The internal jugular vein serves as the medial border during lateral neck dissection. Because of this, it is encountered and manipulated in every level of the lateral, putting it at risk during the procedure. Potential injuries to the vein include hematoma following inadequate ligation of feeding vessels, puncture of the side wall, thrombosis, and complete resection due to tumor invasion. Thrombosis can occur as a reaction from manipulation of the vessel wall or prolonged compression of the vein during surgery. Early postoperative thrombosis can occur in approximately 25% of patients within the first week; however, after at least 3 months from the procedure, only 5% of the thromboses remained.46 Complications from an internal jugular vein thrombosis include septic emboli, pulmonary embolism, and intracranial propagation of the clot. Complete resection of a single internal jugular vein does not typically have morbidity for the patient. The morbidity of resecting both internal jugular veins simultaneously is significant causing severely elevation of intracranial pressure leading to altered level of consciousness, headaches, blindness, and stroke.46
Complications with the common and internal carotid arteries are uncommon intraoperatively, as these vessels are not extensively manipulated during routine dissection. Any intraoperative injury, that is, puncture or inadvertent ligation, should be corrected immediately with a vein patch or reconstruction. Intraoperative consultation with a vascular surgery may be necessary if repair is unsuccessful. Patients must be monitored in the immediately postoperative period for cerebrovascular accident. The most feared long-term complication of any neck dissection is the carotid artery blowout, which occurs in less than 5% of all head and neck cancer patients undergoing surgical resection. Risk factors associated with carotid artery blowout in head and neck cancers include body mass index less than 22.5, open wound to the neck requiring dressing changes, radical neck dissection, and total external beam radiation dose greater than 70 Gy.47 Mortality of this complication can be as high as 60%.48
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