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The technique of mediastinal lymph node dissection was first described in detail by Cahan et al.21 in 1951, when simple pneumonectomy was differentiated from radical pneumonectomy, which included hilar and mediastinal lymph nodes in continuity. Prognosis became linked to lymph node involvement, and lymph node mapping for cancer was established. The technique of mediastinal staging preceding surgical resection has been described.22,23 Mediastinal lymph node dissection at the time of resection will be reviewed herein. While originally performed by means of open thoracotomy, this method of lymph node dissection is now possible by means of VATS technique with a greater technical demand yet comparable results.24–26 Median sternotomy also can be used for extended lymph node dissections, but is not widely used.27 A combination of blunt and electrocautery dissection is fairly standard. A fine metal suction tip can sometimes prove invaluable via VATS approaches. Other techniques that make use of the Harmonic Scalpel (Ethicon Endo-Surgery Inc.; Cincinnati, OH) or the LigaSure (Covidien; Boulder, CO) device are safe and effective as well.
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In routine practice, it is common to dissect the lymph nodes after pulmonary resection. However, if the decision to proceed with resection would be altered by positive N2 involvement, the lymph node dissection is undertaken first. This is especially true when preoperative imaging studies suggest obvious N2 involvement that was not confirmed with prior staging efforts. Previously, cases that involved “surprise” N2 findings may have warranted chest closure and neoadjuvant treatment before resection or may have limited the extent of intended resection.28 However, some of this complex decision-making that had been based on mathematical models and inaccurate assumptions has been revisited. It would now appear that patients with unsuspected N2 disease, who have undergone comprehensive preoperative staging, should get resected even if N2 involvement is discovered at the time of surgery.9 The importance of proper specimen labeling using standard nomenclature cannot be overemphasized. Each lymph node station should be labeled accordingly and submitted separately to avoid confusion among specimens.
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Right-Sided Lymphadenectomy
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Nodal stations to be addressed from the right chest include stations 2 and 4, stations 7 to 9, and N1 stations included in the lobar resection, 10 and 11. The boundaries to the paratracheal nodes (stations 2 and 4) include superior vena cava anteriorly, right brachiocephalic vein and subclavian artery superiorly, trachea and right mainstem bronchus medially, azygos vein and pulmonary artery inferiorly, esophagus and vagus nerve posteriorly, and mediastinal pleura laterally.
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Resection of this nodal packet begins with exposure via incision in the fourth or fifth intercostal space. The lung is retracted inferiorly, and the pleura overlying the azygos vein is opened sharply using a parallel incision (Fig. 76-4). The azygos vein is mobilized and can be divided or resected for complete exposure. This can be done easily by using a vascular stapling device. The dissection then is performed from caudal to cephalad using an Allis or Babcock clamp to grasp the lymph node packet and sweep it off the medial structures. The inferior paratracheal station 4 nodes are carefully dissected at the tracheobronchial angle just above the pulmonary artery and pericardium. A flap of pleura is reflected further in a cephalad direction over the superior vena cava, avoiding the phrenic nerve anteriorly, and over the trachea posteriorly. The station 4 nodes are dissected en bloc from their paratracheal position behind the superior vena cava, which can be retracted anteriorly with a Cushing vein retractor or dental pledget. Small perforating veins draining anteriorly to the superior vena cava are identified and controlled, usually with clips or careful electrocautery. Care must be taken posteriorly to avoid the esophagus, vagus nerve, and membranous trachea along the posterior aspect of the station 4 nodal packet. The dissection is completed at the apex just above the level of the aortic arch toward the right subclavian artery, where the station 2 nodes are found. The recurrent laryngeal branch of the vagus nerve has its takeoff in this location and should be avoided.
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The landmarks associated with the pyramid-shaped subcarinal nodes of station 7 include the tracheal carina superiorly and anteriorly, the esophagus posteriorly, the tracheal bifurcation into the mainstem bronchi laterally, and the pericardium and upper aspect of the inferior pulmonary vein inferiorly. Dissection at this level can be performed from either side, but the left is more challenging owing to the length of the mainstem bronchus and proximity of the aortic arch. The right-sided resection of station 7 subcarinal lymph nodes begins with retraction of the lung anteriorly (Fig. 76-5). The mediastinal pleura is opened posteriorly between the azygos and hilum. The nodal packet is teased out and grasped with a clamp near the lung parenchyma at the bronchus intermedius and superior to the inferior pulmonary vein. The dissection is carried proximally along the mainstem bronchus. Bronchial arterial branches are controlled with clips or careful electrocautery. Proper orientation of the airway must be maintained to avoid inadvertent injury of the left or right mainstem bronchus, and the esophagus is kept retracted posteriorly.
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The remainder of the N2 nodes includes stations 8 and 9. These can be approached from either side fairly equally. The paraesophageal nodes (station 8) are inferior to the carina along the esophagus, whereas the station 9 nodes are within the inferior pulmonary ligament (Fig. 76-6). Most lung resections include mobilization of the inferior ligament either for lower lobe resection or to improve postoperative lung expansion and avoid a residual apical space. Therefore, the approach to dissection of station 9 nodes is straightforward. The lower lobe is oriented such as to put the inferior pulmonary ligament under tension. The ligament then is carefully mobilized in a cephalad direction away from the diaphragm with a combination of blunt and electrocautery dissection. The ligament is composed of anterior and posterior folds, which soon become apparent during the dissection. The mobilization is directed toward the inferior pulmonary vein, with care taken to avoid injury to the adjacent esophagus. Within the areolar tissues overlying the esophagus are usually several station 9 nodes that are elevated and removed. Hemostasis is achieved with control of the small vessels within the ligament inferiorly. Once the esophagus is exposed, other nodes can be sampled from the paraesophageal station 8 position, if present. Care is taken to avoid the vagus nerves, which run along each side of the esophagus laterally at the subcarinal level, as well as bronchial or intercostal arterial branches at all levels.
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Station 10 hilar lymph nodes on the right are located overlying the distal right mainstem bronchus, posterior to the pulmonary artery and inferior to the azygos vein (Fig. 76-7). Exposure is gained by opening the visceral pleura overlying the superior hilum anteriorly with care to avoid the phrenic nerve running along the superior vena cava and pericardium anteriorly. The interlobar station 11 nodes are found near the bifurcation between the right upper lobe and the bronchus intermedius. These are often referred to as “sump” nodes as a result of their interlobar pattern of drainage. Station 12 lobar nodes are encountered when the bronchus is exposed and transected, whereas segmental and subsegmental nodes (stations 13 and 14, respectively) are generally included in the lobectomy specimen.
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Left-Sided Lymphadenectomy
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Nodal stations to be addressed from the left chest include mediastinal stations 4 to 9 and N1 stations included in the lobar resection, 10 to 14. The boundaries for station 5 and 6 nodes include the phrenic nerve anteriorly, the aortic arch and head vessels superiorly, the vagus nerve and descending thoracic aorta posteriorly, the pulmonary artery and pericardium inferiorly, the ascending aorta and trachea medially, and the mediastinal pleura laterally.
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Resection of nodes at stations 5 and 6 begins with a fourth or fifth intercostal approach. The lung is retracted inferiorly, and the mediastinal pleura is opened over the left main pulmonary artery between the phrenic and vagus nerves, and a flap is created from the aortopulmonary window in a cephalad direction along the aortic arch (Fig. 76-8). The prevascular station 6 nodes are found in this location. They can be grasped with an Allis or Babcock clamp, with care taken to avoid the surrounding nerves. Bleeding is controlled with clips or ligatures to prevent an injury from electrocautery. The station 5 lymph nodes in the aortopulmonary window are found more posteriorly along the pulmonary artery near the ligamentum arteriosum. This vestige of the ductus arteriosus may be divided for mobilization of the aorta and pulmonary artery, if needed. The left recurrent laryngeal nerve, which branches from the vagus nerve, must be protected along its course under the aortic arch during dissection. Electrocautery must be minimized or avoided outright. When necessary, the left paratracheal nodes are found along the trachea medial to the ligamentum arteriosum (station 4) and further cephalad above the aortic arch between the left brachiocephalic vein and the left subclavian artery (station 2). These stations, along with station 3, alternatively may be approached posterior to the aortic arch and left subclavian artery by opening the pleura posteriorly and retracting the vessels anteriorly. Intercostal arterial branches need to be divided for this exposure. Care must be given to the recurrent laryngeal nerve as it courses cephalad along the trachea near the esophagus. This method is not widely used in North America.
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The dissection for station 7 from the left is similar to the approach from the right. The lung is retracted anteriorly, and the posterior mediastinal pleura is opened along the groove anterior to the descending thoracic aorta, which is retracted posteriorly (Fig. 76-9). The left mainstem bronchus is exposed, and the subcarinal nodal packet is grasped with a clamp and removed. Dissection may be done in blunt or sharp fashion, during which time attention must be given to hemostasis of the bronchial and intercostal perforating vessels. Care also must be exercised in dissecting the subcarinal nodal packet off the main carina itself and the right mainstem bronchus. The esophagus is deep to the bronchus and is retracted posteriorly with the aorta, whereas the pericardium is found at the anteromedial extent of the dissection and inferiorly at the superior portion of the inferior pulmonary vein.
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Samples from the paraesophageal (station 8) and inferior pulmonary ligament (station 9) nodes are obtained in similar fashion as on the right side once the posterior pleura is opened anterior to the descending aorta from the carina to the diaphragm. Station 10 on the left is found inferior to the pulmonary artery and posterior to the superior pulmonary vein at the distal left mainstem bronchus. Interlobar station 11 nodes are approached via the fissure with the left upper lobe reflected anteriorly or superiorly. The station 12 lobar nodes are found during dissection of the bronchus prior to lobectomy, and the segmental and subsegmental nodes (stations 13 and 14, respectively) are usually found within the specimen.