Neck dissection for differentiated thyroid cancer

INTRODUCTION — Differentiated thyroid cancers, including papillary and follicular, account for >90 percent of thyroid cancer patients [1]. While metastatic disease to regional nodes is frequently identified in patients with papillary thyroid cancer, it is very uncommon in patients with follicular cancer.

Cervical lymphadenectomy, or neck dissection, is the treatment of choice when there is evidence of lymph node metastasis from thyroid cancer. In certain situations, a neck dissection can also be performed "prophylactically" at the time of thyroidectomy to avoid a second operation due to recurrence.

In this topic, we discuss various neck dissection techniques and their applications. Techniques of thyroidectomy are discussed in detail separately. (See "Thyroidectomy".)

ANATOMY AND DEFINITIONS — The neck is divided into six levels (I to VI) and six sublevels (A or B) with regard to its nodal contents (figure 1 and figure 2) [2]:

●Level I – Submental (IA) and submandibular lymph nodes (IB).

●Level II – Upper third of the jugular lymph nodes from the hyoid bone to the base of the skull. This includes those lymph nodes located anterior (IIA) and posterior (IIB) to the spinal accessory nerve.

●Level III – Middle third of jugular lymph nodes, located between the cricoid cartilage and the hyoid bone.

●Level IV – Lower third of jugular lymph nodes, located from the clavicle to the cricoid cartilage.

●Level V – Posterior triangle lymph nodes, located posterior to the sternocleidomastoid muscle, including spinal accessory nodes; above the cricoid cartilage (VA), supraclavicular, and transverse cervical nodes; and below the cricoid cartilage (VB).

●Level VI – Central neck lymph nodes located between the carotid arteries from the innominate artery to the hyoid bone. This includes the pretracheal, prelaryngeal, and paratracheal lymph nodes.

A radical neck dissection involves the removal of all nodal and fibrofatty tissue from levels I to V, including sacrificing the sternocleidomastoid muscle, the spinal accessory nerve, and the internal jugular vein.

A modified radical neck dissection involves removal of all nodal and fibrofatty tissue from levels I to V but preserves one or more of the sternocleidomastoid muscle, the spinal accessory nerve, and the internal jugular vein.

For most patients with thyroid cancer, removal of the affected lymph nodes does not require sacrificing any of the critical structures. In addition, it is uncommon that a patient with thyroid cancer would require removal of level I lymph nodes. Therefore, most patients undergo a compartment-oriented selective neck dissection, which is removal of all of the fibroadipose tissue and lymphatic tissues en bloc from a given compartment (ie, central, lateral) within the neck, while preserving critical structures (figure 2 and figure 3) [3]:

●A central neck dissection entails removal of the lymph nodes from level VI, including the prelaryngeal and pretracheal nodes, and at least one paratracheal lymph node basin. Central neck dissection may be unilateral or bilateral.

●A lateral neck dissection includes the removal of the lymph nodes from level II through V.

Nonanatomical cervical lymph node resection, commonly referred to as "berry picking," where only the involved nodes are removed, should not be performed, because of a higher local recurrence rate compared with that of compartment-oriented neck dissections (100 versus 9 percent) [4].

LYMPH NODE METASTASIS IN DIFFERENTIATED THYROID CANCER

Incidence

Papillary thyroid cancer — Metastatic disease to regional lymph nodes is common in patients with papillary thyroid cancer. Palpable nodal disease is present in approximately 5 to 10 percent of patients with papillary thyroid cancer; a preoperative neck ultrasound can detect lymph node disease in up to 30 percent of patients [5-8].

Standard histologic techniques (hematoxylin and eosin stain) typically reveal positive lymph nodes in 20 to 50 percent of patients undergoing an elective neck dissection for papillary thyroid cancer [9]. However, after immunohistochemical evaluation (ie, cytokeratin stain), up to 90 percent of patients will have microscopic metastatic disease [10-12]. It appears that many patients have microscopic regional lymph node disease that never becomes clinically apparent. (See 'Prognosis' below and "Papillary thyroid cancer: Clinical features and prognosis", section on 'Prognostic features'.)

Follicular thyroid cancer — By contrast, follicular thyroid cancer metastasizes via the hematogenous rather than the lymphatic route [13]. As a result, <5 percent of patients with follicular thyroid cancer develop nodal metastasis. (See "Follicular thyroid cancer (including oncocytic carcinoma of the thyroid)", section on 'Metastases'.)

Pattern of spread — Central neck, or level VI, lymph nodes are typically the first site of regional spread of papillary thyroid cancer [11]. Papillary thyroid cancer spreads in a stepwise fashion from the thyroid to the central neck and then laterally to the jugular chain nodes (figure 1 and figure 2). Level III and level IV are the most common sites of nodal metastatic disease in the lateral neck compartment, while disease is rarely identified in level I nodes [14].

If there is nodal involvement identified in the lateral neck, it is presumed that there is disease in the central neck as well. Thus, if nodal disease is identified in the lateral neck, both a central and lateral neck dissection should be performed.

"Skip" metastasis, in which lateral neck involvement is seen in the absence of central neck nodal disease, can occur in up to 22 percent of patients and is most commonly seen with superior pole thyroid tumors [15,16].

Risk factors — Cervical lymph node metastasis from papillary thyroid cancer is associated with several well-described factors, including multifocality, extrathyroidal extension, larger tumor size, younger age, aggressive variants, and the presence of BRAF mutation [17-20].

Prognosis — Metastatic disease to regional lymph nodes at the time of presentation may increase the risk of cervical recurrence but does not appear to negatively impact survival [21-23]. (See "Papillary thyroid cancer: Clinical features and prognosis", section on 'Histology' and "Follicular thyroid cancer (including oncocytic carcinoma of the thyroid)", section on 'Lymph node involvement'.)

Lymph node involvement in papillary thyroid cancer can be macroscopic (identified on preoperative imaging or intraoperative inspection) or microscopic (identified on pathologic review only). Macroscopic lymph node involvement is associated with a high rate of local recurrence (10 to 42 percent) [21,22,24-27]. Lymph node factors associated with a higher risk of local recurrence include more than five positive lymph nodes, high ratio of positive to negative lymph nodes (ie, lymph node ratio), and the presence of extranodal extension [21,28].

The association between microscopic nodal disease detected following a prophylactic neck dissection and recurrence of local lymph node disease is controversial [24,25,29,30]:

●In one trial, 181 patients without evidence of lymph node disease were randomly assigned to total thyroidectomy alone or total thyroidectomy plus a prophylactic central neck dissection [31]. Microscopic lymph node disease was identified in 46.2 percent of patients who underwent neck dissection. At five years, there was no difference in rates of structural recurrence or persistent disease between the two groups.

●However, in a multicenter retrospective study, 103 clinically node-negative patients who were treated with total thyroidectomy alone had a higher recurrence rate (3.9 percent) than 30 patients treated with total thyroidectomy plus a unilateral or bilateral central neck dissection (0 percent) [32]. Lymph nodes were positive in 23.3 percent of patients undergoing a unilateral dissection and 63.3 percent undergoing a bilateral dissection.

The prognosis of differentiated thyroid cancer remains excellent even in patients with lymph node involvement (>90 percent 10 year survival) [1,29]. Metastatic disease to regional lymph nodes at the time of presentation does not appear to have a significant impact on overall survival [21-23]. As an example, the 5 and 10 year disease-specific survival rates in patients with lymph node metastasis from papillary thyroid cancer were similar to those in patients without lymph node metastasis (98 versus 100 percent and 95 versus 100 percent, respectively) [29].

Metastatic disease to regional lymph nodes for patients <45 years of age is not an independent risk factor for disease-specific survival [23,29,33-38]. In a retrospective review of 11,453 patients with papillary thyroid cancer, the four-year disease-specific survival for patients <45 years old was 99 percent, independent of the presence or absence of lymph node involvement. Kaplan-Meier age-stratified subgroup analysis found age >45 years to be associated with a higher mortality rate [23]. The four-year disease-specific survival was particularly worse for patients >45 years old with positive nodes in the lateral and mediastinal compartments (level II to VA and VB/VII) compared with those with positive nodes in the central compartment (level VI). (See "Papillary thyroid cancer: Clinical features and prognosis", section on 'Prognostic features' and "Follicular thyroid cancer (including oncocytic carcinoma of the thyroid)", section on 'Prognostic features'.)

CHOOSING A NECK DISSECTION TECHNIQUE

Staging evaluation — A preoperative ultrasound to assess for regional nodal disease in the neck is an essential part of the staging workup of all patients with a preoperative diagnosis of thyroid cancer (image 1) [39,40].

Computed tomography (CT) scans and magnetic resonance imaging (MRI) scans are used selectively in the preoperative evaluation of patients with thyroid cancer and are most beneficial in patients with extensive nodal involvement or in patients with thick necks in whom the resolution of ultrasound may be limited [41,42].

The staging of thyroid cancer and a review of the utility of ultrasonography are reviewed separately. (See "Differentiated thyroid cancer: Clinicopathologic staging" and "Overview of the clinical utility of ultrasonography in thyroid disease", section on 'Lymphadenopathy'.)

At thyroidectomy, it is not uncommon to discover central compartment nodal disease not identified on preoperative ultrasound. Thus, the surgeon should always inspect the central compartment nodes and be prepared to perform central neck dissection if they appear abnormal. Suspected lymph node metastasis may be confirmed by intraoperative frozen section examination.

The decision to perform a neck dissection and the choice of a neck dissection technique are determined by whether and where lymph node metastasis has been detected (algorithm 1).

No known nodal disease

Central neck compartment — Patients with follicular thyroid cancer have a low risk of nodal disease (<5 percent) [13]. Thus, in patients known to have follicular thyroid cancer preoperatively (which is an uncommon situation), a central neck dissection should not be performed prophylactically without any evidence of lymph node metastasis. Prophylactic central neck dissection is not appropriate for most patients receiving thyroidectomy for indeterminate fine-needle aspiration biopsy results.

A prophylactic central neck dissection (level VI) for patients with papillary thyroid cancer is controversial [26,27,30-32,43-51]. We use a selective approach, based upon patient risk factors and the experience level of the surgeon [43]:

●We consider a prophylactic central neck dissection (ipsilateral or bilateral) in patients with large papillary thyroid cancer (T3 or T4 lesions) (table 1) or the presence of extrathyroidal tumor extension. Some surgeons will perform a prophylactic neck dissection based on carrier status of BRAF mutations from a fine needle aspiration (FNA) sample, but this remains controversial.

●We perform a near-total or total thyroidectomy without prophylactic central neck dissection in patients with small (T1 or T2) lesions and without high-risk features.

Our approach is consistent with the American Thyroid Association (ATA) consensus guidelines [9] and the American Association of Endocrine Surgeons guidelines [52]. (See "Differentiated thyroid cancer: Surgical treatment", section on 'Prophylactic lymph node dissection' and "Differentiated thyroid cancer: Overview of management", section on 'Choice of surgical procedure' and "Oncogenes and tumor suppressor genes in thyroid nodules and nonmedullary thyroid cancer".)

A prophylactic central neck dissection at the time of thyroid surgery may help avoid a reoperation but may increase perioperative morbidity, particularly when performed by less experienced surgeons [53-55]. While older studies suggested a reduced risk of nodal recurrence and improved survival with a prophylactic central neck dissection [56,57], such benefits were not demonstrated by other studies [55].

A meta-analysis of 17 nonrandomized comparative studies showed that patients with papillary thyroid cancer without clinical evidence of nodal metastasis who underwent total thyroidectomy with prophylactic central neck dissection had a lower risk of locoregional recurrences (risk ratio [RR] 0.66, 95% CI 0.49-0.90), especially in the central neck compartment (RR 0.35, 95% CI 0.18-0.68), compared with those without neck dissection [58]. However, prophylactic central neck dissection was associated with higher rates of overall morbidity (odds ratio [OR] 2.56, 95% CI 1.75-3.74), including those of temporary (OR 2.37, 95% CI 1.89-2.96) and permanent hypocalcemia (OR 1.93, 95% CI 1.05-3.57).

In a randomized trial, 60 patients with clinically node-negative papillary thyroid cancer underwent total thyroidectomy with or without prophylactic central neck dissection [59]. Although 28 percent of patients who underwent neck dissection had microscopic lymph node involvement, the oncologic outcomes at one year were not different between the two groups. Another randomized trial failed to demonstrate any impact of prophylactic central neck dissection on nodal recurrence or persistence but did show that central neck dissection reduced the need for additional treatments with radioactive iodine [31]. (See 'Morbidity rates' below.)

Lateral neck compartment — Lateral neck lymph nodal involvement occurs in approximately 20 to 30 percent of patients with thyroid cancer [60]. Regional nodal disease is generally identified by ultrasound preoperatively or postoperatively. Because the lateral neck compartment is not entered during a total thyroidectomy, there is no added risk to doing a lateral neck dissection in a delayed fashion if disease is identified after the initial operation.

While microscopic disease is common in the lateral neck, routine lateral neck dissection has never been shown to benefit long-term survival [21,43]. Given that lateral neck dissection is associated with considerable morbidity but no survival benefit, we reserve it for patients who have proven nodal disease in the lateral neck, rather than performing it prophylactically at the time of thyroid surgery. (See 'Known nodal disease' below.)

Known nodal disease — A neck dissection for differentiated thyroid cancer (papillary and follicular) is performed as a therapeutic procedure when nodal disease is suspected based upon the clinical examination or ultrasound evaluation and confirmed with fine-needle aspiration (cytology and thyroglobulin washout). This is recommended by both the ATA and the National Comprehensive Cancer Network (NCCN) [9,61]. (See "Thyroid biopsy", section on 'Lymphadenopathy'.)

A therapeutic neck dissection can be performed with the initial thyroidectomy, as a (delayed) secondary procedure after the initial thyroidectomy, at the time of a local nodal recurrence in the absence of widespread or distant diseases, or as a reoperation in patients who have had a previous neck dissection in the same compartment [62,63]. (See "Differentiated thyroid cancer: Surgical treatment", section on 'Therapeutic lymph node dissection' and "Differentiated thyroid cancer: Overview of management", section on 'Choice of surgical procedure'.)

Recurrent nodal disease — In patients who develop nodal or local recurrence after previous surgery for differentiated thyroid cancer, we perform surgical removal when feasible in order to avoid complications from continued tumor growth, to facilitate surveillance of thyroglobulin levels, and to minimize the amount of radioactive iodine that patients receive.

However, due to the risks of reoperation, we usually do not consider operative intervention until the lesion is >8 to 10 mm in size. For lesions <1.5 cm, we utilize the blue dye technique or same-day ultrasonographic skin marking to facilitate intraoperative localization. (See 'Preoperative localization of recurrent disease' below.)

The following approach is consistent with the current ATA guidelines [9]:

●In the clinical setting of a biopsy-proven recurrence ≥8 mm in the central neck and ≥10 mm in the lateral neck, we advocate surgical resection of the lesion.

•For patients with nodal recurrence in a field that has not been dissected, we perform a formal compartment-oriented neck dissection.

•For patients with biopsy-proven nodal recurrence following thyroidectomy and a formal neck dissection, we proceed with a focused removal of the involved lymph node(s) and any adjacent nodes.

●In the clinical setting of a biopsy-proven recurrence <8 mm in the central neck and <10 mm in the lateral neck, we perform a formal compartment neck dissection if the patient has not had a prior lymphadenectomy. If the recurrence is in a reoperative bed, we favor observation and serial imaging until the lesion enlarges further. We then perform a focused removal of the involved lymph node(s) or a therapeutic lymph node dissection of that level if the level has not been previously dissected.

Patients with a low risk of recurrence may be managed nonoperatively with serial imaging. In 166 patients with suspected nodal recurrences who were followed without surgery, only 29 percent of the lesions grew by >3 mm in 3.5 years, and 14 percent resolved [64]. Another option that can be used in case of isolated recurrence, especially if the patient is a high-risk operative candidate, is ethanol ablation [65-67].

PREOPERATIVE PREPARATION

Prophylactic antibiotics — Thyroidectomy and neck dissection are both classified as clean operations, with the risk of infection <1 percent [68]. Because of the low infection risk, routine prophylactic antibiotics have not been proven beneficial. Nevertheless, preoperative antibiotics can be administered to select patients who are at high risk of developing wound infections, including those who have medical comorbidities or are immunocompromised. (See "Thyroidectomy", section on 'Antibiotics'.)

Venous thrombosis prophylaxis — Patients undergoing a regional thyroid lymphadenectomy are at a very low risk for developing a deep venous thrombosis (DVT). The reported risk of DVT in this population is 0.16 percent [69], while the risk of bleeding complications is higher (0.96 percent). Thus, the risks and benefits of DVT prophylaxis must be balanced carefully in this population.

For high-risk patients, we use a preoperative subcutaneous dose of unfractionated heparin in addition to intermittent pneumatic compression devices. Prevention of DVT is discussed in detail separately. (See "Prevention of venous thromboembolic disease in adult nonorthopedic surgical patients".)

Preoperative localization of recurrent disease — Distortion of the tissue planes due to scarring makes a reoperation for metachronous recurrence of nodal disease technically challenging. Preoperative localization of recurrent disease is a useful adjunct for any reoperative neck dissection [70-74].

Ultrasound guidance can be used preoperatively to inject either a very small amount of blue dye [75] or a charcoal suspension [76] to mark the location of the pathologic nodes, which allows the surgeon to localize the pathologic nodes among the scar tissues within the neck. Intraoperative ultrasound can also be used to augment localization. (See "Differentiated thyroid cancer: Overview of management", section on 'Management of persistent or recurrent disease'.)

A prospective study of 10 patients with isolated, nonpalpable recurrences found that injection of blue dye under ultrasound guidance was feasible and detected nodes as small as 6 mm without complications [75]. Another prospective study of 15 consecutive patients found that colloidal charcoal injected under ultrasound guidance 1 to 15 days before the operation could be identified in or near 16 of 19 (84 percent) recurrent lesions [76].

CENTRAL COMPARTMENT NECK DISSECTION

Extent of central neck dissection — The central compartment neck dissection extends superiorly to the hyoid bone and inferiorly to the innominate (brachiocephalic) artery (figure 1). The lateral border of dissection is the ipsilateral carotid artery, the anterior border is the superficial layer of the deep cervical fascia, and the posterior border is the deep layer of the deep cervical fascia, which may be deep to the carotid artery. The number of lymph nodes contained within the central neck varies greatly between patients. An autopsy study identified between 1 and 16 lymph nodes in the central neck, with 0 to 7 lymph nodes in each paratracheal space and an additional 0 to 8 in the pretracheal space [77].

Technique for central neck dissection — An initial central neck dissection is typically performed with the same patient positioning, type of incision, exposure, drains, and closure as described for thyroidectomy. The approach to thyroidectomy is reviewed separately. (See "Thyroidectomy", section on 'Dissection of the thyroid gland'.)

Although the anatomic landmarks are the same for initial and reoperative procedures, the landmarks may be distorted and challenging to identify if the neck dissection is performed in the same compartment after a previous cervical operation such as thyroidectomy, parathyroidectomy, carotid endarterectomy, cervical disc surgery, or lymphadenectomy. Thus, in the reoperative setting, a fresh incision can be made directly over a localized level VI lymph node in order to avoid extensive dissection and complications [70]. Furthermore, such reoperations should be performed by a surgeon skilled in reoperative thyroid operations.

The standard approach to initial neck dissection for patients with thyroid cancer is compartment oriented. The general principles of a central compartment neck dissection include (figure 4) [3]:

●Identifying the recurrent laryngeal nerve at the posterior suspensory ligament of Berry (lateral thyrohyoid ligament) (figure 5). The recurrent laryngeal nerve lies lateral to the ligament. Preserve the recurrent laryngeal nerve caudally along its entire course.

●Dissecting the fibroadipose tissues anterior and medial to the recurrent laryngeal nerve and its branches, medially to laterally, using an en bloc technique and gentle traction on the specimen.

●Dissecting the tissues posterior to the recurrent laryngeal nerve laterally and inferiorly, sweeping the mass of lymphatic and fibroareolar tissues medially and inferiorly from the level of the hyoid bone superiorly to the innominate artery inferiorly.

●Identifying the upper (embryologically superior) parathyroid gland, typically 1 to 2 cm cranial to the junction of the recurrent laryngeal nerve with the inferior thyroid artery, and within 1 cm of the entry point for the recurrent laryngeal nerve into the ligament of Berry and the cricoid cartilage (figure 6).

●Identifying the superior thyroid artery, which provides arterial blood supply to the upper parathyroid glands in most patients. Preserve the adjacent superior laryngeal nerve and its branches as well as the parathyroid gland and its vascular pedicle [78].

●Identifying the inferior parathyroid gland, located anterior to the recurrent laryngeal nerve. The inferior gland is most often found in the thyrothymic tract or just inside the thyroid capsule on the inferior portion of the thyroid lobes. Free the gland from its medial fibroareolar attachments, and sweep it laterally on its vascular pedicle. The blood supply is generally from the inferior thyroid artery, which is nearly always preserved.

●Preserving the inferior parathyroid gland. Every attempt should be made to preserve the parathyroid gland in situ, if feasible. Often, the lower parathyroid gland can be mobilized laterally and preserved with its inferior pedicle. However, when there is bulky central neck nodal disease, this can be challenging. If a parathyroid gland becomes dusky in color, indicating devascularization, an autotransplantation can be performed after confirming that it is indeed a parathyroid gland by intraoperative frozen section. Most surgeons agree it is difficult to preserve the lower parathyroid glands in situ, and some advocate routine autotransplantation [79]. (See "Thyroidectomy", section on 'Parathyroid autotransplantation'.)

●Dissecting caudally toward the sternal notch. If available, the Harmonic scalpel cutting and coagulation device may facilitate the separation of central compartment contents from the lateral strap muscle fibers as well as help in the management of associated small blood vessels. Identify and preserve the recurrent laryngeal nerve along its course from the ligament of Berry to the thoracic outlet while resecting all lymphatic tissues anterior to it.

●Including the thymic tissue with the specimen, especially if abnormal nodes are palpated within the gland.

●Do not "berry pick." Isolated removal of only the visible or clinical involved lymph nodes violates the principles of compartment-oriented dissection and will result in higher recurrence rates [4].

THERAPEUTIC LATERAL COMPARTMENT NECK DISSECTION — A compartment-oriented approach is standard when performing a lateral neck dissection; there is no role for "berry picking" of lymph nodes (figure 2 and figure 7). In most cases, a lateral compartment neck dissection for thyroid cancer does not entail a radical or modified radical neck dissection. (See 'Anatomy and definitions' above.)

Extent of lateral compartmental dissection — The extent of a lateral compartment lymph node dissection for papillary thyroid cancer is controversial [80]. The extent of dissection generally depends upon the location of the nodal disease (eg, most commonly level III and IV) (see 'Pattern of spread' above). No randomized trials have been performed to determine the appropriate extent of the lateral compartmental dissection.

The consensus statement from the American Thyroid Association recommends that a comprehensive lateral neck dissection for thyroid cancer include removal of lymph nodes from levels IIA, III, IV, and VB [81]. The highest rates of nodal involvement include levels III (77 percent), IV (62 percent), IIA (49 percent), and VB (40 percent) [82,83].

While some authors support a comprehensive nodal dissection of levels II to V for all patients with thyroid cancer [81,83], we advocate a more selective approach with a compartment-oriented dissection determined by the extent of nodal involvement identified on preoperative imaging and intraoperative assessment. We routinely dissect levels III, IV, and the anterior portion of level VB in all lateral neck dissections but only include levels I, II, and the remainder of level VB in the presence of involved nodes in the adjacent compartment (figure 2).

Using a selective approach, a level II neck dissection is required in approximately 21 percent of patients undergoing a therapeutic neck dissection [14]. Most positive level II nodes are located in level IIA, and without clinical or radiographic involvement, level IIB dissection is unnecessary in most patients [82,84].

Patients with level II disease typically have positive level III lymph nodes. Therefore, a level II node dissection may be omitted if there is no clinical or histologic evidence of positive level III nodes and no evidence of macroscopic extranodal extension [85]. Based upon a retrospective review of 52 patients with papillary thyroid cancer with no clinical suspicion of positive level II nodes, occult disease was identified in 19 percent (10 patients) [86]. Occult disease was identified only in those patients with imaging suspicious for level III or IV nodal involvement or histologic evidence of positive lymph nodes in level III.

Level VB nodes are positive in 12 to 40 percent of patients, but involvement of level VA is rare (figure 2) [83,86]. If there is no evidence of posterior nodal involvement in level V, we confine our dissection anterior to the spinal accessory nerve in order to avoid injury to the nerve. The border between levels III, IV, and V is somewhat arbitrary, likely contributing to the variable rate of dissection and node positivity.

Technique for a selective lateral neck dissection — The approach to a lateral compartment neck dissection includes (figure 1 and figure 2 and figure 7):

Incision — The incision for a lateral neck dissection depends upon the operative setting and surgeon preference. It can be a low collar incision or a lateral extension of a higher thyroidectomy incision. If additional exposure is needed to reach level II, the lateral extent of the incision can be brought up along the posterior aspect of the sternocleidomastoid muscle, or a second incision can be placed in a high neck crease to facilitate exposure to this region (figure 8). An ultrasound performed after the patient has been positioned on the operating table can be helpful to map the extent of the nodal disease and guide optimal incision placement.

Dissection of level III and level IV — We routinely resect levels III, IV, and the anterior portion of level VB in all lateral neck dissections (figure 2).

●Begin the dissection inferiorly at the level of the clavicle. Continue the dissection along the internal jugular vein to the anterior scalene muscle.

●Identify the fibroareolar plane posteriorly.

●Use sharp dissection techniques, and avoid using electrocautery in the vicinity of major neurovascular structures (eg, jugular vein, vagus nerve).

●Preserve the thoracic duct as it empties into the internal jugular vein, near the junction with the subclavian vein. A simulated Valsalva maneuver, performed by suspending mechanical ventilation and applying manual compression to the ventilation bag, can facilitate identification of the duct and recognition of an injury. If the thoracic duct is divided, it should be ligated securely but gently to avoid leakage.

●Identify the vagus nerve within the carotid sheath, posterior and medial to the internal jugular vein. The vagus nerve is spared while dissecting along the vein.

●Continue the dissection superiorly and laterally, identifying and preserving the phrenic nerve, located just posterior to the plane of dissection and anterior to the scalene muscle (figure 9 and figure 10). The phrenic nerve is left intact adherent to the scalene muscles while the tissue superior to the nerve is resected.

●Preserve the cervical plexus nerves when possible while dissecting the nodal tissue from level III (figure 11). The cervical plexus nerves cross the field of dissection.

Dissection of level II and level V — We only include dissection levels I, II, and the posterior level VB in the presence of involved nodes in the adjacent compartment (III, IV, and anterior VB).

●Identify the hypoglossal nerve at the superior extent of the lateral dissection, as it crosses superior to the bifurcation of the carotid artery, near the facial vein (figure 12).

●Identify the spinal accessory nerve at the lateral extent of the superior dissection (figure 12). The spinal accessory nerve is the landmark that divides level II into levels IIA and IIB, where it can be identified superior to the greater auricular nerve, which originates posterior to the sternocleidomastoid muscle. Avoid retraction or dissection along the nerve, which is particularly vulnerable to injury during levels IIB and VA dissections.

●Continue the dissection posteriorly into level VA and superiorly to level IIA. If no further disease is identified, the dissection is concluded here. However, if macroscopic nodal disease is identified at level IIA, proceed with the removal of level IIB nodes.

●Insertion of a drain should be done selectively if at all, as it will not prevent bleeding or seroma formation [87-89]. If there is any suspicion of injury to the thoracic duct, a drain should be placed.

INTRAOPERATIVE ISSUES

Intraoperative monitoring — At the surgeon's discretion, intraoperative monitoring of the recurrent laryngeal nerve can be used. The technique for intraoperative nerve monitoring is reviewed elsewhere. (See "Thyroidectomy", section on 'Intraoperative nerve monitoring'.)

Intraoperative ultrasound can aid in tumor identification, particularly during a reoperation when the recurrence may not be easily identifiable [71-73]. Using preoperative and intraoperative ultrasound and localization techniques can guide incision placement, direct the dissection, and minimize the risks in the reoperative setting [70-76]. (See 'Preoperative localization of recurrent disease' above and 'Outcomes' below.)

Intraoperative challenges — The greatest technical challenges to avoiding injury to vital structures are encountered in the reoperative setting secondary to distortion or obliteration of the anatomic landmarks [90]. Besides that, central and lateral compartment neck dissections each have a unique set of intraoperative challenges.

The intraoperative challenges for a central neck dissection are similar to those for a thyroidectomy and include identification and preservation of nerves (eg, recurrent laryngeal nerve, superior laryngeal nerve), vascular pedicles (eg, superior thyroid artery and vein), parathyroid glands, the trachea, and the esophagus (figure 1) [45,91,92]. (See "Thyroidectomy", section on 'Complications'.)

During a lateral neck dissection, the vagus, phrenic, spinal accessory, hypoglossal, greater auricular, sympathetic chain, and cervical sensory nerves are at risk of injury. The spinal accessory nerve is at greatest risk, particularly when levels IIB and VA nodes are dissected (figure 12 and figure 2) [93,94].

Additionally, densely adherent nodal disease to the internal jugular vein can require ligation and resection of the vein. However, this procedure can only be safely performed unilaterally in one operative setting to avoid obstruction of cerebral venous outflow [95-97]. (See 'Technique for a selective lateral neck dissection' above.)

POSTOPERATIVE MANAGEMENT — Postoperative care after neck dissections is similar to that after a thyroidectomy and includes management of pain, nausea, and observation for complications such as hypocalcemia, chyle leak, and hematoma formation. Patients are typically admitted for overnight observation but can be discharged home after less extensive neck dissections. (See "Thyroidectomy", section on 'Postoperative care'.)

All patients are educated regarding the symptoms of hypocalcemia (eg, perioral numbness, paresthesias of the hands or feet, muscle cramps). After discharge, patients are often instructed to take 1 to 2 grams of oral calcium supplementation (elemental calcium given as calcium carbonate or calcium citrate). A typical dose is 2 grams twice daily, but the dose is adjusted to control symptoms and maintain a low-normal serum calcium concentration. (See "Clinical manifestations of hypocalcemia", section on 'Acute manifestations' and "Treatment of hypocalcemia".)

For patients undergoing a central neck dissection, serum calcium and parathyroid hormone (PTH) levels can be obtained in the recovery room for outpatients or on the morning of postoperative day 1 prior to discharge for those who are admitted. Calcium supplementation can be based upon the postoperative PTH level using the following algorithm [98]:

●PTH >10 pg/mL – Supplement with 1 to 4 g of calcium orally daily.

●PTH between 5 to 10 pg/mL – Add 0.25 mcg of calcitriol twice daily to calcium supplementation.

●PTH <5 pg/mL – Add 0.5 mcg of calcitriol twice daily to calcium supplementation.

If PTH testing is not available, then symptoms or an algorithm based upon serum calcium levels can be used to determine the need for calcium supplementation (table 2).

Alternatively, some surgeons prescribe calcium supplementation to all patients in the postoperative period, given the minimal risks and cost of routine calcium supplementation [20]. (See "Thyroidectomy", section on 'Calcium supplementation' and "Treatment of hypocalcemia" and "Differentiated thyroid cancer: Surgical treatment", section on 'Hypoparathyroidism' and "Surgical management of hyperthyroidism", section on 'Hypocalcemia'.)

If used, a drain is typically removed on postoperative day 1. If a drain was placed to observe for a chyle leak, the patient is given a fatty food challenge and the drain contents examined for milky, opalescent appearance of lymphatic fluid. If a small chyle leak is identified, it may cease with conservative management, such as medium-chain triglyceride diet or parenteral nutrition. If the output cannot be controlled by diet modification, reoperation with ligation of the thoracic duct, fibrin sealant placement, or flap closure may be required [99]. (See "Etiology, clinical presentation, and diagnosis of chylothorax", section on 'Pathogenesis and etiology' and "Management of chylothorax".)

Thyroid hormone replacement following a thyroidectomy for differentiated thyroid cancer is discussed separately. (See "Differentiated thyroid cancer: Surgical treatment", section on 'Postoperative thyroid hormone therapy'.)

OUTCOMES

Mortality rates — The 30 day mortality rate after thyroidectomy and neck dissection for differentiated thyroid cancer is less than 1 percent [100].

Morbidity rates — The most common complications following a neck dissection for differentiated thyroid cancer are similar to those following a thyroidectomy and include nerve injury, hypocalcemia, hematoma/seroma formation, and injury to the trachea and esophagus. The extent of the surgical procedure, the experience of the surgeon, and prior neck surgery all contribute to the risk of surgical complications [101,102]. (See "Thyroidectomy", section on 'Complications'.)

Morbidities of central neck dissection — In a review of 17 retrospective studies including 1929 patients undergoing a central neck lymph node dissection, the complications and their respective prevalences were [43]:

●Transient hypocalcemia – 3.6 to 60 percent

●Permanent hypocalcemia – 0 to 14.4 percent

●Transient recurrent laryngeal nerve injury – 0 to 25 percent

●Permanent recurrent laryngeal nerve injury – 0 to 11.5 percent

While some authors suggest that there is no increased risk of complications when a central neck dissection is performed in conjunction with a total thyroidectomy [44], others have found higher complication rates with an added neck dissection, especially when performed by less experienced surgeons [43,44,53-55,91,103-105].

As an example, a review of 1087 patients found higher rates of transient hypoparathyroidism after unilateral or bilateral central neck dissection compared with after total thyroidectomy alone (unilateral: 36.1 versus 27.7 percent; bilateral: 51.9 versus 27.7 percent) [53]. In a randomized trial, permanent hypoparathyroidism was also more common after central neck dissection than after a total thyroidectomy alone (19.4 versus 8.0 percent) [31].

A bilateral central neck dissection is associated with a higher rate of complications than a unilateral central neck dissection. As an example, in a retrospective review of 103 patients with papillary thyroid cancers <2 cm, patients undergoing a bilateral dissection were significantly more likely to develop transient hypocalcemia compared with patients undergoing a unilateral dissection (48.0 versus 20.5 percent) [50].

Reoperation in the central neck can be technically challenging. However, the complication rates are not different from those of initial operations when reoperations are performed by experienced surgeons [43,48,63,90,106]. Based upon a retrospective review of 295 patients undergoing central neck dissections, patients undergoing a reoperation (n = 106) had similar rates of permanent hypocalcemia (0.5 versus 0.9 percent), hematoma formation (1.1 versus 0.9 percent), and permanent hoarseness (2.9 versus 1.9 percent) compared with patients undergoing an initial neck dissection [106]. Only transient hypocalcemia was more common after a reoperation (41.8 versus 23.6 percent).

Morbidities of lateral neck dissection — A lateral compartment lymph node dissection, when performed by an experienced surgeon, is associated with a low risk of injury to the spinal accessory, hypoglossal, and vagus nerves; the sympathetic chain (Horner syndrome); and the thoracic duct [104]. Reoperation for nodal disease in the lateral neck is not associated with any higher risk of complications if the lateral neck has not been dissected during the original operation [106].

In addition to the more serious complications such as nerve injury, postoperative seromas are common after a lymph node dissection and typically appear four to five days after the operation and then resolve spontaneously. Seromas are not prevented by drain placement at the time of operation [89,107]. Since a small seroma is difficult to discern from normal postoperative swelling, the incidence of this complication is difficult to define. However, occasionally seromas become large and symptomatic and require percutaneous aspiration for symptom relief. Seromas requiring percutaneous drainage are uncommon, occurring in <7 percent of patients [89,107].

Nodal recurrence — The nodal recurrence rate following a therapeutic neck dissection ranges from 28 to 38 percent [21,62,106]. In a retrospective review of 45 patients undergoing a therapeutic neck dissection for recurrent thyroid cancer, 17 patients (38 percent) developed a second recurrence [62]. If the nodal disease was located outside a previously dissected level at the time of the therapeutic neck dissection, the overall nodal recurrence rate was 28 percent [62]. (See 'Recurrent nodal disease' above.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Thyroid surgery".)

SUMMARY AND RECOMMENDATIONS

●For patients with differentiated thyroid cancer but without evidence of nodal involvement (algorithm 1):

•A prophylactic neck dissection is not performed for patients known preoperatively to have follicular thyroid cancer, because the risk of nodal disease is low.

•We do not routinely perform central neck dissection (level VI) for papillary thyroid cancer, since the benefits of prophylactic dissection appear small and the risk of transient complications is high. However, for those with a large primary cancer (T3/4) or high-risk features for recurrence (eg, BRAF mutations, extrathyroidal tumor extension), a prophylactic central neck dissection is an option that can potentially negate a reoperation. (See 'Choosing a neck dissection technique' above and "Differentiated thyroid cancer: Surgical treatment", section on 'Approach to lymph node dissection'.)

●For patients with differentiated thyroid cancer and evidence of nodal involvement (ie, clinical or radiographic evidence confirmed by fine-needle aspiration), we recommend a therapeutic neck dissection (algorithm 1) (Grade 1B). (See 'Choosing a neck dissection technique' above and "Differentiated thyroid cancer: Surgical treatment", section on 'Approach to lymph node dissection'.)

●For patients with a nodal recurrence following a thyroidectomy without a previous lymphadenectomy, we recommend a therapeutic compartment-oriented neck dissection (algorithm 1) (Grade 1B). (See 'Known nodal disease' above.)

●For patients with a recurrence following a therapeutic neck dissection, we suggest a focused excision of the lesion that is ≥8 mm in the central neck and ≥10 mm in the lateral neck (Grade 2C). If the recurrence is located in an anatomic level not previously dissected, we suggest a therapeutic lymph node dissection of that level (Grade 2B). Suspected nodal recurrences that are smaller may be observed with serial imaging (algorithm 1). (See 'Recurrent nodal disease' above.)

●The central compartment neck dissection extends superiorly to the hyoid bone and inferiorly to the innominate (brachiocephalic) artery (figure 1). The lateral border of dissection is the ipsilateral carotid artery, the anterior border is the superficial layer of the deep cervical fascia, and the posterior border is the deep layer of the deep cervical fascia, which may be deep to the carotid artery. It can be performed in conjunction with a thyroidectomy or as a separate procedure for recurrent differentiated thyroid cancer. (See 'Central compartment neck dissection' above.)

●The extensiveness of a lateral compartment lymph node dissection generally depends upon the location of the nodal disease (eg, most commonly level III and IV) and surgeon preference and is controversial. For therapeutic purposes, we routinely dissect levels III, IV, and the anterior portion of level VB. We dissect levels II and posterior VB if diseases are present in adjacent levels. "Berry picking" of clinically involved nodes should not be performed for therapeutic purposes. (See 'Therapeutic lateral compartment neck dissection' above.)

●Nodal recurrence rate following a therapeutic neck dissection ranges from 28 to 38 percent. Reoperative neck dissection is most technically challenging and risky for complications secondary to distortion or obliteration of the anatomic landmarks by scar tissues. Preoperative marking with blue dye or charcoal suspension and intraoperative ultrasound can facilitate identification of pathologic nodes. When necessary, a fresh incision can be made directly over a localized lymph node to avoid extensive dissection. (See 'Recurrent nodal disease' above and 'Preoperative localization of recurrent disease' above and 'Intraoperative challenges' above and 'Nodal recurrence' above.)

●When performed by experienced surgeons, neck dissection is associated with low morbidity and mortality rates. Major morbidities of neck dissection are similar to those of thyroidectomy and include nerve injury, hypocalcemia, hematoma/seroma formation, and injury to the trachea and esophagus. (See 'Outcomes' above.)