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Address reprint requests and correspondence: Ralph P. Tufano, MD, FACS, Department of Otolaryngology/Head and Neck Surgery, Johns Hopkins University School of Medicine, 601 N. Caroline Street, JHOC 6th Floor, Baltimore, MD 21287
The central compartment of the neck is a common site of local metastasis for thyroid carcinoma. Therefore, knowledge of the surgical techniques for performing a central compartment neck dissection is important for any surgeon who manages patients with thyroid cancer. The use of a standardized surgical approach to the central compartment can minimize morbidity and ensure comprehensive removal of lymph nodes within this region. This article describes the authors' method for performing a comprehensive central compartment neck dissection.
The boundaries of the anterior compartment of the neck, also known as level VI, are defined by the carotid arteries laterally, hyoid bone superiorly, and suprasternal notch inferiorly (Figure 1). Lymph nodes in the anterior compartment consist of the precricoid or Delphian lymph node; prelaryngeal, pretracheal, paratracheal lymph nodes located in the tracheoesophageal groove; and the perithyroidal lymph nodes. The inferior border of the central compartment neck dissection is located below the sternal notch at the level of the innominate artery and brachiocephalic vein. Thus, the lymph nodes in level VII, or the superior mediastinal nodes, are incorporated as part of a comprehensive central compartment neck dissection for thyroid cancer (Figure 1).
Figure 1Boundaries of the central compartment of the neck. The boundaries of the anterior compartment of the neck, also known as level VI, are defined by the carotid arteries laterally, hyoid bone superiorly, and suprasternal notch inferiorly. The inferior border of the central compartment neck dissection is located below the sternal notch at the level of the innominate artery and brachiocephalic vein. Therefore, a comprehensive central compartment neck dissection incorporates both level VI and level VII lymph nodes.
A central compartment neck dissection can be performed as a prophylactic or therapeutic dissection. Strong indications for a prophylactic dissection include patients with medullary thyroid carcinoma,
carcinoma exhibiting local invasion (eg, trachea, esophagus), poorly differentiated thyroid carcinoma, and high-risk, well-differentiated thyroid carcinoma, such as those patients with preexisting lateral neck disease, a family history of thyroid cancer, and/or a documented BRAF mutation.
Appropriately, controversy exists in the literature as to whether to perform a prophylactic central neck dissection in all patients with well-differentiated thyroid cancer. The benefit of improved local disease control, without an obvious survival benefit, must be carefully weighed against the risks of hypoparathyroidism and recurrent laryngeal nerve injury. Further investigation needs to be performed at a molecular biology level before strict indications for prophylactic central neck dissection are determined in this patient population.
Therapeutic neck dissections are recommended for patients with documented metastatic disease based on manual palpation, imaging and/or cytologic evaluation by fine-needle aspiration of involved lymph nodes. Therefore, careful preoperative high-resolution neck ultrasound for the contralateral thyroid lobe and cervical (central and lateral) lymph nodes should be performed in patients undergoing surgery for a malignant fine-needle aspiration result of a thyroid nodule.
The rationale for a standardized compartment-oriented central neck dissection is that it may decrease the risk of recurrence of thyroid cancer within the central neck and, if universally adopted, would allow us to assess outcomes more accurately. Furthermore, because reoperation in the central neck compartment for recurrent disease may increase the risk of hypoparathyroidism and recurrent laryngeal nerve injury as compared with primary surgery, a thorough preoperative work-up and more aggressive initial operation may be warranted when indicated.
The procedure is performed in the operating room setting with the patient under general anesthesia. The patient and equipment should be set up as routine for thyroid surgery. The use of a nerve-monitoring system may be a helpful adjunct to test the electrophysiologic integrity of the recurrent laryngeal nerve before commencing dissection on the contralateral side, especially if one is performing a prophylactic dissection. The nerve-monitoring system is particularly helpful in reoperative cases in which scar tissue in a previously operated neck may make identification of the recurrent laryngeal nerve difficult. The placement of a shoulder roll can help bring the contents of the neck anteriorly and facilitate surgical dissection in the central neck compartment. A standard Kocher incision as small as 4 cm in length and 2 fingerbreadths above the sternal notch provides sufficient exposure for dissection. Skin flaps are raised superiorly to the thyroid notch and inferiorly to the sternal notch, respectively.
A vertical incision is made between the sternohyoid and sternothyroid muscles extending from the thyroid notch to the level of the sternal notch. The fascial plane between the sternohyoid and sternothyroid muscles is defined and the plane separated to maximize lateral retraction of the strap muscles. For reoperative cases, the sternothyroid and, if necessary, the sternohyoid muscles can be transected horizontally and separated off the floor of the thyroid bed to maximize exposure for the planned central neck dissection. This may be necessary in the reoperative setting due to the presence of fibrosis that may otherwise limit craniocaudal exposure in this area. The prelaryngeal lymph node, located anterior to the cricothyroid membrane, usually is dissected at the time of mobilization of the thyroid pyramidal lobe and isthmus and the pretracheal lymph nodes are dissected off the surface of the trachea at the time of thyroidectomy or can be included in the central compartment neck dissection.
The carotid artery on either side is skeletonized from the level of the thyroid cartilage down to the clavicle (Figure 2). The lateral side of the paratracheal lymph nodes is then separated from the carotid sheath, and the dissection line is extended inferiorly to the innominate artery or brachiocephalic vein. A branch of the carotid artery may be present (thyroid Ima) in some cases. This branch should be ligated and cut without injury to the carotid artery itself. Next, the recurrent laryngeal nerve (RLN) is identified, usually at the time of the thyroidectomy or, for reoperative cases, identified inferiorly distant from the previously operated bed.
Figure 2Central neck anatomy as it relates to the carotid artery. The carotid artery is skeletonized from the level of the thyroid cartilage down to the clavicle. The lateral side of the paratracheal lymph nodes is separated from the carotid sheath, and the dissection line is extended inferiorly to the innominate artery or brachiocephalic vein.
For reoperative cases, the right RLN typically can be found as it enters the central compartment from underneath the carotid artery/innominate artery junction below the second tracheal ring. The left RLN is typically drawn medially against the trachea and can safely be found below the second tracheal ring. Although the superior boundary of the central neck compartment is the hyoid bone, lymph nodes typically are not found above the junction of the inferior thyroid artery and insertion point of the RLN into the cricothyroid membrane. Radiographic imaging or direct visualization at the time of surgery is usually helpful in determining if this upper part of the central neck compartment requires dissection.
Dissection for the right central neck compartment and left central neck compartment differ slightly as the result of the anatomical course of the nerve. Because the right RLN loops around the subclavian artery and ascends apart from the tracheoesophageal groove, lymph nodes are present both anterior and deep to the right RLN dividing the right paratracheal lymph nodes into an anterior and a posterior compartment (Figure 3). After identification of the recurrent laryngeal nerve, the operating surgeon may choose to stand at the head of the patient's bed to dissect carefully along the RLN inferiorly to the level of the clavicle with a Crile or fine-tipped dissector to allow for atraumatic mobilization from the surrounding lymph node bearing tissue (Figure 4A).
Figure 3The right RLN bisects the anterior and posterior paratracheal lymph node compartments. Dissection for the right central neck compartment and left central neck compartment differ slightly as the result of the anatomical course of the nerve. Because the right RLN loops around the subclavian artery and ascends apart from the tracheoesophageal groove, lymph nodes are present both anterior and deep to the right RLN dividing the right paratracheal lymph nodes into an anterior and a posterior compartment.
Figure 4(A) Dissection of right RLN with a fine-tipped dissector. After identification of the RLN, the operating surgeon may choose to stand at the head of the patient's bed to dissect carefully along the RLN inferiorly to the level of the clavicle with a Crile or fine tipped dissector to allow for atraumatic mobilization from the surrounding lymph node bearing tissue. (B) to remove both the anterior and posterior lymph node compartments the right RLN needs to be transposed which can be achieved without direct retraction of the nerve or without using a nerve hook. (C) The posterior compartment lymph nodes are then mobilized anteriorly and transposed under the nerve. The lymph node compartment is then mobilized off the prevertebral fascia and esophagus and the dissection carried down to the level of the innominate artery to incorporate the superior mediastinal lymph nodes with the anterior and posterior compartment lymph nodes.
To remove both the anterior and posterior lymph node compartments the right RLN needs to be transposed, which can be achieved without direct retraction of the nerve or without using a nerve hook (Figure 4B). The posterior compartment lymph nodes are then mobilized anteriorly and transposed under the nerve (Figure 4C). The fibrofatty tissue and lymph nodes that are inferior to the inferior thyroid artery and deep to the RLN are then mobilized off the prevertebral fascia and esophagus. The dissection of the posterior portion of the fibrofatty tissue should be carried down to the level of the innominate artery to incorporate the superior mediastinal lymph nodes with the anterior compartment lymph nodes. In addition, the upper pleural membrane is sometimes visible behind the posterior portion of the fibrofatty tissue and lymph nodes in this area, especially in obese patients. Injury to the pleural membrane can result in a pneumothorax; therefore, careful dissection should proceed in this area.
In contrast, the left RLN loops around the aortic arch and travels along the tracheoesophageal groove. The esophagus is present immediately behind the left RLN. Unlike the right side, there usually is a paucity of lymph nodes present immediately deep to the left RLN. Therefore, after the paratracheal lymph nodes are separated from the carotid sheath (Figure 5A), dissection of the lymph nodes medial and lateral to the left RLN, without transposition of the nerve itself, is usually sufficient for the left side (Figure 5B). The dissection should be carried inferiorly to the level of the innominate artery or brachiocephalic vein, allowing for incorporation of the superior mediastinal lymph nodes.
Figure 5(A) Dissection of the left RLN. The lateral side of the paratracheal lymph nodes is dissected away from the carotid sheath, and the dissection line is extended inferiorly to the innominate artery or brachiocephalic vein. (B) The left RLN loops around the aortic arch and travels along the tracheoesophageal groove. Because the esophagus is present immediately behind the left RLN, there is usually a paucity of lymph nodes deep to the left RLN. Therefore, mobilization of the lymph nodes medial and lateral to the left RLN, without transposition of the nerve itself, is usually sufficient for the left side.
Complications associated with central compartment neck dissection include hypoparathyroidism and recurrent laryngeal nerve injury. At the completion of the central compartment neck dissection, the viability of the parathyroid glands should be assessed. Typically, the superior parathyroid glands can be identified and remain in situ, especially by preserving the inferior thyroid artery and its superior branches. The inferior parathyroid glands may have to be resected to allow a comprehensive lymphadenectomy within the central compartment or if they are adherent to bulky nodal disease or disease with gross extracapsular spread. If the inferior parathyroid gland was removed with the central compartment lymph nodes, or if any gland's viability is in question, a small piece of the gland should be sent for frozen histopathologic analysis to confirm the presence of parathyroid tissue. Once confirmed, the parathyroid gland should be separated from the lymph nodes, minced into 1-mm cubes, and inserted into the sternocleidomastoid muscle or brachioradialis muscle of the forearm and the site of reimplantation marked with a surgical clip.
Discussion
A standardized approach has been developed for dissection of levels in the lateral neck, and we advocate a similar standardization of surgical technique for the central compartment. Standardization of the surgical approach minimizes morbidity and ensures comprehensive removal of lymph nodes in the central compartment likely to harbor disease which can reduce the need for reoperative dissections and, thus, decrease the risk of hypoparathyroidism and/or recurrent laryngeal nerve injury. This standardization will also allow clinicians to accurately assess the efficacy of prophylactic and therapeutic central neck dissection in the management of thyroid cancer.
References
Moley J.F.
Fialkowsky E.A.
Evidence based approach to the management of sporadic medullary thyroid carcinoma.
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