When treating patients with non–small-cell lung cancer (NSCLC), it is important to assign an accurate clinical or pathologic stage to the disease at the time of diagnosis. This adds value to the process of selecting the most appropriate therapy for the individual patient, whether it be surgical resection, neoadjuvant chemotherapy or radiotherapy, or definitive chemoradiation. The current cancer staging convention uses the basic descriptors originally proposed by Denoix¹ primary tumor (T), lymph node involvement (N), and tumor metastasis (M). The contemporary classification system was adopted worldwide in 1997 after features of the 1986 combined American Joint Committee on Cancer and the International Union Against Cancer TNM staging system² were reconciled with the 1983 American Thoracic Society statement on cancer staging. The organization responsible for updating this system is the International Association for Lung Cancer Staging which revised the staging system in 2009³ and will do so again in 2016. The value of classifying NSCLC patients according to a uniform staging system that has prognostic implications based on stage grouping is difficult to overstate.

Clinical staging can be determined on the basis of CT scanning, MRI, and CT/PET scanning. Pathologic staging requires biopsy, which can be obtained from cervical or anterior mediastinoscopy, during video-assisted thoracic surgery (VATS) approaches, less commonly by means of open thoracotomy, and more recently by fine-needle aspiration performed during endoscopic or endobronchial ultrasound sampling.^4,5 Lymph node involvement has important implications for surgical treatment strategies for lung cancer.^6–8 Patients without lymph node involvement (N0) or those with limited involvement (N1), which is usually determined at the time of surgery, are candidates for resection based on T and M status. Most patients with contralateral or supraclavicular disease (N3) or T4 involvement are not resectable (stage IIIB). The usual approach in stage IIIA patients with ipsilateral mediastinal nodal involvement (N2) involves either neoadjuvant chemotherapy or chemoradiation, followed by resection if appropriate, when N2 status is determined prior to resection. In some cases, surgically detected N2 disease can be discovered at the time of resection by means of lymph node dissection in conjunction with the pulmonary resection.⁹ There is no doubt that sampling of lymph nodes in some fashion is useful for staging and prognostic purposes. However, the extent of lymph node dissection is controversial, and the benefits of systematic sampling versus complete mediastinal lymph node dissection or extended lymph node dissection are still under review.^10–13

To unify the two most widely used systems of lymph node mapping in NSCLC, the American Joint Committee on Cancer and the International Union Against Cancer adopted a standardized method of classifying lymph node stations in 1996. This was outlined in 1997 by Mountain and Dresler based on the work of Naruke and the American Thoracic Society and the North American Lung Cancer Study Group.¹⁴ The most notable difference between these systems was the boundary between peribronchial hilar (N1) and paratracheal mediastinal (N2) lymph nodes comprising stations 4 and 10, respectively. These are now separated by the pleural reflection between the visceral pleura (station 10) and the mediastinal pleura (station 4) (Fig. 76-1). The other definitions remained basically the same. The nodal station descriptions of mediastinal, hilar, and intrapulmonary are designed to be reproducible, and stage groupings are based on studies of prognostic factors, including metastasis.

Regional lymph node stations for lung cancer staging are shown in Figure 76-2. Any double-digit station is classified as N1. Single digit lymph nodes are N2. The anatomic definitions for lymph node mapping are shown in Table 76-1. Involvement of contralateral mediastinal or hilar stations, as well as ipsilateral supraclavicular or scalene nodes, is considered N3 disease. Survival is inversely proportional to nodal involvement and was validated in a database analysis by Mountain and Dresler.¹⁴

The distribution and likelihood of lymph node metastasis based on lobar location of the cancer has been described.¹⁵ In Cerfolio and Bryant’s study of 954 patients, incidence and location of N2 disease were distributed as shown in Figure 76-3, based on location of the primary lung lesion. This knowledge can help advocates of mediastinal lymph node sampling to target the lymph node stations to be obtained at the time of resection.^16,17 Others perform radical lymphadenectomy routinely with each resection regardless of primary lobar location.¹⁸ This is thought to improve the yield of lymph node sampling, detect noncontiguous lymph node involvement (skip metastases), and improve survival.^11,13,19,20

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.

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.

Right-Sided Lymphadenectomy

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.

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.