Accurate evaluation of regional lymph node metastasis can be determined only by complete lymph node dissection. If an extended or total resection of all accessible nodes is not performed, the presence and extent of metastasis may be underestimated. The majority of patients with lung cancer are not candidates for definitive surgery; however, the lymph node mapping schema is useful for clinical staging and for investigations such as correlative studies of diagnostic and evaluative examinations--radiographs, computed tomography, positron emission tomography, immunoscintigraphy, or transbronchial needle biopsy performed at bronchoscopy or biopsies at mediastinoscopy and mediastinotomy, or by transesophageal ultrasound.

The medical literature confirms that lymph node metastasis has a profound effect on survival, and that prognosis is better when such an extension is confined to the peribronchial nodes lying within the visceral pleural envelope, N1, as opposed to the nodes lying within the mediastinal pleural envelope, N2. In the staging system this is expressed, in terms of survival percentage, as N0 > N1 > N2 > N3. This general observation is both reliable and valid. Within the spectrum of the N1 and N2 categories, however, the relationship to prognosis of metastasis to specific lymph nodes, the number of nodes and level of nodes involved, the influence of intranodal and extranodal disease, and the influence of primary tumor characteristics and histologic features is not fully known. The present unified lymph node mapping schema provides for collecting data with consistency to enable study of these patterns of metastatic spread and translate the information for useful clinical and research purposes.