Role of Thoracoscopic Lymph Node Staging for Lung and Esophageal Cancer

Introduction

Staging of thoracic malignancies is of the utmost importance to the proper treatment of patients with thoracic malignancies. The 1988 American Joint Committee on Cancer Staging (AJCC) criteria defined the tumor, node, metastasis (TNM) staging for lung and esophageal carcinoma [1,2]. These staging criteria are based on survival statistics, which allow the stage groups to be used to predict outcome after cancer treatment. In addition, the definitive staging of patients with thoracic malignancies correctly allocates patients to treatment regimens appropriate for their disease stage. This enables adjuvant and neoadjuvant treatment to be given to patients who will truly derive the greatest benefit and in whom it will be worthwhile to undertake the possible risks and side effects of such treatment.

Thoracoscopy is an excellent means for staging intrathoracic malignancies. Thoracoscopy affords an excellent view of the entire thoracic cavity, including the mediastinum, and thus, is a good tool for biopsy of mediastinal lymph nodes. Thoracoscopic evaluation of the pleural cavity can clearly show invasion of the chest wall by intrathoracic malignancies. It also permits evaluation of the entire parietal pleural surface and the visceral pleural surface of the lung.

Importance of Lymph Node Staging

Lung Cancer

The modern lung cancer staging system was described by Naruke and Mountain [3,4]. The clinical importance of this system is its ability to successfully predict the outcome of patients on the basis of TNM staging. Most important is the distinction between hilar and mediastinal lymph node involvement in these patients (Figures 1 and 2). Not only has this staging system proven to be a useful prognosticator, but treatment strategies based on the presence or absence of mediastinal lymph node involvement have proven to be important in managing patients with lung cancer [5]. Although Whittesey [6] described the usefulness of the CT scan in predicting lymph node invasion in 1988, this noninvasive tool still remains only approximately 85% accurate in predicting malignant lymph nodes when lymph nodes are > 1.5 cm in size.

Esophageal Cancer

Lymph node stage is an important independent prognostic indicator in esophageal carcinoma (Figures and 4), as noted by Ellis et al [7]. Skinner et al [8] stressed the importance of node stage and recommended extended resection for esophageal cancer depending on operative lymph node staging.

Akiyama et al [9] found that the pattern of lymph node spread in esophageal cancer showed metastasis to at least one thoracic node station in almost all cases. Metastasis to distant lymph nodes was not uncommon in their series.

Preoperative staging of thoracic lymph node stations would be likely to reflect the actual lymph node status, provided that all lymph node stations could be assessed prior to surgery. Preoperative staging of esophageal cancer may allow us to allocate adjuvant therapy to patients in whom it would be most beneficial.

Surgical Staging Procedures

The classic approaches to mediastinal lymph node sampling include a variety of invasive techniques. Mediastinoscopy, described by Harken et al [10] in 1954 and popularized by Carlens [11] in 1959, is the standard tool for mediastinal lymph node biopsy. One limitation of this technique is the difficulty in sampling the aortopulmonary window and left para-aortic lymph nodes. Although extended transcervical mediastinoscopic biopsy of the aortopulmonary window is possible, it is a relatively complicated procedure [12]. Also, biopsy of subcranial lymph nodes may be difficult, especially when nodes are inferior and posterior. Lastly, mediastinoscopy also is not useful for biopsying masses in the anterior mediastinum, as this region is inaccessible to the mediastinoscope.

The Chamberlain procedure (parasternal anterior mediastinotomy) provides an excellent approach to lymph node biopsy of the anterior mediastinum [13]. It is particularly useful for biopsy of the aortopulmonary window and para-aortic lymph nodes on the left but can also access lymph nodes or mediastinal masses on the right. The mediastinoscope can be inserted into the pleural space at the same sitting to further stage local disease.

Desauliers et al described a combination of mediastinoscopy, pleuroscopy, and bimanual palpation to document lymph node involvement in the mediastinum [14]. The disadvantages of the Chamberlain procedure include the frequent requirement for rib resection, with resultant pain, longer hospital stay for recuperation, and a more disfiguring cosmetic result, compared with mediastinoscopy.

Although proven in lung cancer, only recently has the importance of mediastinal lymph nodes been clarified in patients with esophageal cancer. In 1993, the initial results with thoracoscopic staging of esophageal cancer were reported. Although thoracic nodes were correctly staged in all patients, celiac nodes were missed in two patients [15]. Since then, routine thoracoscopic and laparoscopic lymph node staging has been used in patients with esophageal carcinoma with excellent results. Although as yet, there is no consensus regarding the role of surgical staging in patients with esophageal cancer, the results of pilot trials in which patients were treated with neoadjuvant therapy promise an important future role for this new technique in separating advanced esophageal cancer from local disease.

Role of Thoracoscopy

Lung Cancer

For patients with lung cancer, thoracoscopy is an excellent tool to augment other noninvasive and minimally invasive staging procedures. T3 lesions with suspicious direct spread to the chest wall can be evaluated prior to formal resection. Similarly, in patients who have suspicious T4 lesions with questionable mediastinal invasion, thoracoscopy can differentiate between abutment of the mediastinal pleura and mediastinal invasion by tumor. Thus, thoracoscopy can help avoid unnecessary thoracotomy in high-risk patients in whom one would want to avoid an unnecessary chest wall incision.

Thoracoscopy is also useful for evaluating primary tumor status in patients with pleural effusions. In those with suspicious T4 lesions, thoracoscopy may be useful in finding and evaluating malignant invasion of the pleura or a malignant pleural effusion. It can help determine the presence of pleural implants or invasion of the pericardium, the vagus, phrenic, or recurrent laryngeal nerves. Again, thoracoscopy can help avoid an unnecessary thoracotomy for attempted resection in the patient who is found to have gross disease spread.

Thoracoscopy is a particularly useful tool in evaluating mediastinal lymph nodes. It is used as a complement to standard cervical mediastinoscopy in evaluation of levels 2 through 11 mediastinal and hilar lymph nodes. Although mediastinoscopy is excellent for evaluating the upper and lower paratracheal nodes (American Thoracic Society [ATS] levels 2 through 4), evaluation of the subcranial nodes (level 7) or aortopulmonary and periaortic lymph nodes (ATS levels 5 and 6) is either difficult or impossible by standard techniques. We no longer perform the Chamberlain procedure (parasternal mediastinotomy) to evaluate the aortopulmonary window but instead use thoracoscopy to assess this area [16]. Thoracoscopy is especially helpful in patients who have lymph nodes in the aortopulmonary window that are > 1 cm or patients who have left-sided lung tumors in whom cervical mediastinoscopy does not show positive mediastinal lymph nodes.

Levels 8 and 9 paraesophageal and inferior pulmonary ligament lymph nodes are also considered N2 mediastinal lymph nodes according to the staging criteria. Despite this, the preoperative staging of these lymph node stations is almost never accomplished due to the inaccessibility of this region to cervical mediastinoscopy. Thoracoscopy is a useful tool to biopsy these stations preoperatively when they are enlarged. Thoracoscopy may help establish whether these stations are actually of the same prognostic importance as are other mediastinal (N2) lymph nodes.

Some surgeons have even suggested the use of routine thoracoscopic evaluation of the pleural cavity prior to all thoracotomies for lung cancer resection. The rationale behind this approach is to rule out previously unsuspected T4 lesions in patients who would otherwise undergo an unnecessary thoracotomy. At present, other than serving as a very useful training tool, there is no clear advantage of this technique in routine cases.

Esophageal Cancer

Despite aggressive surgical treatment of esophageal cancer, high perioperative morbidity and mortality are typical. Despite attempts at using combination therapy with chemotherapy, radiation therapy, and surgical resection in patients with esophageal cancer, 5-year survival rates have been disappointingly low [17-19]. If a subgroup of patients with a relatively good prognosis could be selected, survival rates with combination therapy and even standard surgical therapy might be significantly improved.

If it were possible to achieve accurate preoperative staging in esophageal cancer, patients could be separated prospectively into those likely to have residual local or lymphatic disease and those in whom complete resection is likely to be attainable. This would enable the physician to allocate modalities, such as adjuvant chemotherapy and radiation therapy, to the appropriate patient populations who would derive the greatest benefit, and thus, would limit the morbidity associated with these treatments.

Although surgery for esophageal carcinoma achieves the best immediate palliation currently available for dysphagia, many esophageal carcinoma lesions are found at the time of surgery to be full thickness (T3, T4) or to involve lymph nodes (N1). Mediastinal invasion by an esophageal carcinoma precludes a safe resection. The pathologic stage differs from the clinical stage in up to two-thirds of cases showing full-thickness tumors or lymphatic spread. Surgical staging thus may identify those individuals who are candidates for aggressive palliative or nonsurgical treatment regimens and avoid unnecessary surgical resections.

Huang and Sun have shown that, among patients with esophageal carcinoma, the 5-year survival rate in patients without lymph node metastases was 45%, as compared with 13% in those with lymph node spread. Likewise, when more than five nodes were involved, the survival rate was 0%, as opposed to 15% when fewer than five nodes were involved [20]. Hagen et al [21] have recently claimed an improved survival benefit for patients with complete lymphadenectomy associated with esophagectomy for distal third and gastroesophageal junction tumors. In 1986 Dagnini et al [22] described the routine use of laparoscopy before undertaking esophagectomy for esophageal cancer. Of 369 patients, intra-abdominal metastases were noted in 14% and celiac lymph node metastases in 9.7%.

In 1977 Murray et al [23] described the use of mediastinoscopy and "mini-laparotomy" in patients with esophageal cancer. In their series of 30 patients, 5 had positive lymph nodes at mediastinoscopy and 16 had positive nodes at mini-laparotomy. This finding supports the use of an operative staging tool to differentiate localized from advanced esophageal cancer.