The system for classifying regional lymph nodes for lung cancer staging was developed in response to a recognized need for a single system of nomenclature that could be used internationally. The current recommendations are derived from the best features of differing nodal maps used over the past decade^5,14-15, and a study of the literature dealing with the anatomy of the mediastinal pleura and patterns of lymph node drainage. An artist's depiction of the mediastinal and intrapulmonary lymph nodes cannot depict precisely the anatomy of the tracheal tree and its known variations; therefore, it is important to relate the drawings to the definitions of the lymph node stations with respect to anatomic landmarks. Fourteen numbered stations for classifying the status of regional lymph nodes are shown in Fig. 51a. The mediastinal lymph nodes, N2, are assigned single digit numbers (1 through 9) and the intrapulmonary, including hilar, lymph nodes are assigned double digit numbers (10 through 14). The anatomic landmarks delineating each nodal compartment are described in the accompanying table.

The current system resolves the problem of defining and classifying mediastinal and intrapulmonary, including hilar, lymph nodes as follows: Anatomic landmarks identify all lymph node stations within the mediastinal pleural reflection as N2, and all lymph node stations distal to the mediastinal pleural reflection and within the visceral pleura as N1. As the point of fusion of the two pleural reflections cannot be determined clinically, the definable upper lobe bronchi are used as the most appropriate landmarks for this point (Fig. 51a). The most proximal nodes in the N1 category, Nos. 10L and 10R are designated hilar nodes, and 11 R/L through 14 R/L are intrapulmonary nodes with specific designations related to the location on or between the bronchi.

Researchers may wish to divide the lower peritracheal nodes into superior (No. 4s) and inferior (No. 4i) groups in order to study the relationship of specific levels of lymph node metastasis to survival. Anatomic landmarks for this division are described in the definitions on pages 46-47.