The intrapulmonary lymph nodes, when present, are located most often just beneath the visceral pleura. Rarely, a peripheral lymph node may present as a solitary peripheral nodule, as reported by Greenberg,¹⁷ Houk and Osborne,²¹ and Ehrenstein.¹³ In addition to these infrequent, radiographically identified intrapulmonary lymph nodes, Trapnell⁶² reported the identification of other intrapulmonary lymph nodes in the substance of the lung by a combined technique of injection of the subpleural lymphatics and subsequent radiologic evaluation of autopsy lung specimens. Intrapulmonary nodes were observed in 5 of 28 injected specimens, an incidence of 18%. The actual location of these nodes was undocumented. However, Trapnell⁶³ was able to identify peripheral lymph nodes radiologically in only 1 of 92 inflated lungs obtained at autopsy, an incidence of just over 1%. Despite this early study, Dail¹¹ reported that intraparenchymal lymph nodes could be identified in about 10% of resected lobes when they were sought, and Kradin and associates²⁶ had previously recorded that all such nodes were anthracotic and were not encapsulated. In Kradin and associates’²⁶ report, the identified lymph nodes were solitary in 65% of the cases and multiple in the remainder; in 22%, two lymph nodes were found, and in 12% three or more were identified. The multiple nodes may be in the same lobe in 40% of the cases in which they are found, but in 60%, the lymph nodes are located bilaterally. Most are in the size range of 0.5 to 1.0 cm; occasionally, nodes as large as 1.5 cm are identified. Only rarely is a larger one present. All these intraparenchymal lymph nodes are within 1 cm of the pleura, adjacent to it, or in an interlobular septum. With rare exception, these lymph nodes are found only in adults and are identified more commonly in individuals >50 years of age.

With high-resolution computed tomography (HRCT), some of the small lesions identified in patients with multiple metastases to the lung are proved subsequently to be small peripheral lymph nodes. Ohbuchi and associates⁴⁸ reported excision by video-assisted thoracic surgery (VATS) of 10 intrapulmonary lymph nodes suspected as malignant lesions, either primary or secondary, over a 1-year period. The average size of the pulmonary nodes was 5.9 mm, and all were located in the lower lobes: seven on the left and three on the right. Over a 2-year period in nine patients, Nagahiro and colleagues³⁷ resected 13 intrapulmonary lymph nodes that had been identified on chest radiographs in three patients and on HRCT in the other six. The characteristics of these nodes on HRCT were that the borders
were sharp, the shapes were ovoid, all were located in the lower portion of the lungs in a subpleural location, and the interval density was high and homogeneous. No borders were irregular, although short spicules could be present, and none contained cavities or calcifications. As the aforementioned authors—as well as Ohbuchi⁴⁸ and Yokomise⁶⁹ and their associates—have pointed out, these lesions must be differentiated from small malignant nodules.

Nagaishi³⁸ noted that segmental lymph nodes are related to the bifurcation of the segmental bronchi or may lie in the bifurcation of the branches of the associated pulmonary arteries and may extend out to the fifth- or sixth-order segmental bronchi.

The lobar bronchopulmonary lymph nodes are found at the angles formed by the origins of the various lobar bronchi and lie in close association with the bronchus or the adjacent pulmonary vessels. The hilar lymph nodes are situated alongside the lower portions of the main bronchi or the respective pulmonary artery and the pulmonary veins lying within the visceral pleural reflections.

The number of bronchopulmonary lymph nodes is variable. These lymph nodes more frequently are present in greater numbers in children than in adults. Borrie⁷ suggests that the maximal development of these nodes is reached by the end of the first decade of life; then these lymph nodes gradually atrophy and disappear during adulthood. The presence of pulmonary infection or malignancy greatly affects the number of bronchopulmonary lymph nodes that may be identified.

In a study of 200 operative specimens of lungs containing lung cancer, Borrie⁷ identified lymph nodes in 13 locations in the right lung and 15 in the left that are now considered bronchopulmonary lymph nodes. These sites are listed in Table 6-1 and are shown schematically in Figures 6-1 and 6-2. The incidence of bronchopulmonary lymph nodes present in each location is listed in Table 6-2.

The hilar lymph nodes are contiguous with the lobar lymph nodes distally as well as with the mediastinal lymph nodes proximally. The hilar lymph nodes lying superior to the right mainstem bronchus classically have been considered to extend up to the inferior border of the azygos vein, but this concept was questioned by Tisi and associates⁶¹ in their recommendations about the location of the various mediastinal lymph node stations. The lymph nodes medial to the right mainstem bronchus may be considered as hilar nodes when located away from the tracheal carina and within the visceral pleural sheath, but as they become subjacent to this structure, they are best termed subcarinal lymph nodes and thus belong to the lymph nodes of the mediastinal compartment.

On the left side, the anatomic separation between the hilar and the mediastinal lymph nodes proximally is at an imaginary plane connecting the lateral surfaces of the ascending and descending portions of the thoracic aorta. The left hilar nodes are located medial, anterior, posterior, and lateral to the left mainstem bronchus in order of decreasing frequency in number. The hilar nodes located anteriorly are found in relation to the left mainstem pulmonary artery. Proximally, these latter nodes are contiguous with the subaortic lymph nodes of the mediastinum, including the lymph node located at the site of the ligament arteriosum, the so-called Bartello’s node. The nodes on the medial surface of the main-stem bronchus, as their position advances upward, become subcarinal in location.

The two most common locations in which lobar lymph nodes are found in the right lung are between the upper-lobe bronchus and middle-lobe bronchus: the area that Borrie⁶ termed the right bronchial sump (the superior interlobar lymph node of Rouvière⁵⁹) and the region just below the middle-lobe bronchus adjacent to the lower lobe bronchus (the inferior interlobar lymph node of Rouvière⁵⁹). In the left lung, the most common location is at the angle of the left-upper-lobe bronchus and the lower-lobe bronchus. Borrie⁶ designated this area as the left lymphatic sump, and the nodes found here correspond to the left interlobar node of Rouvière.⁵⁹

The lymph nodes in the lymphatic sump of the right lung lie in relation to the bronchus intermedius (Fig. 6-3). According to Nohl-Oser,⁴⁷ a constant lymph node is found at the upper posterior end of the major fissure in the angle between the right-upper-lobe bronchus and the bronchus intermedius. A branch of the bronchial artery coursing over the posterior aspect of the right main bronchus leads to it (Fig. 6-4). Another lymph node is found on the interlobar portion of the pulmonary artery where this vessel gives off the posterior ascending segmental branch to the posterior segment of the upper lobe and the superior segmental artery to the superior segment of the lower lobe. Inferiorly, this lymph node is contiguous with a constant node lying above the superior segmental bronchus of the lower lobe. Other
lymph nodes of the sump are found at the base of the major fissure lying closely alongside the interlobar portion of the pulmonary artery or in the bifurcations of its branches. Frequently, lymph nodes are identified more anteriorly, lying among the upper lobe branches of the superior pulmonary vein.

In addition to the sump nodes, the other interlobar lymph nodes can be grouped, according to Borrie,⁷ into those of the upper, middle, and lower lobes. The lymph nodes of the right upper lobe are located above the upper-lobe bronchus, medial to it, and just behind it. Those lying above the bronchus merge with the hilar nodes of the distal portion of the right mainstem bronchus. The lymph nodes of the middle lobe, in addition to the subjacent node below the middle-lobe bronchus (the inferior interlobar node of Rouvière⁵⁹) are located lateral to the middle-lobe bronchus near its confluence with the lower-lobe bronchus as well as medial to it. The right-lower-lobe lymph nodes, in addition to the aforementioned superior and inferior sump nodes, are found medial to the superior segmental bronchus or between it and the basal bronchi. Lymph nodes are present also in relationship to the basal stem of the lower-lobe bronchus and lie on its medial aspect, lateral to it, and between the anterior and medial basal bronchi.

The collection of lymph nodes described by Nohl^44,45 and Nohl-Oser⁴⁷ as composing the left lymphatic sump lies between the upper and lower lobes in the main fissure (Fig. 6-5). A constant node is present in the bifurcation between the upper- and lower-lobe bronchi in close relation to the origin of the lingular (inferior division) branch of the upper lobe (Fig. 6-6). A small bronchial arterial branch passing across the membranous portion of the left main bronchus leads to it. Other lymph nodes are found lying on the interlobar portion of the left pulmonary artery in the fissure and in the angles formed by its branches. Another constant node is described, which is found above and posterior to the left interlobar bronchus. This node is contiguous with a node lying in the angle formed by the interlobar bronchus and the takeoff of the bronchus to the superior segment of the lower lobe.

In addition to the left lymphatic sump nodes, Borrie⁷ noted that lymph nodes of the left upper lobe are present medial, posterior, and lateral to the upper-lobe bronchus. Lymph nodes are present also between the segmental divisions of this bronchus.

The lymph nodes of the left lower lobe are located more commonly in the vicinity of the superior segmental bronchus of the lobe. They are found medial, above, and inferior to it, between it and the basal bronchi. The other lobar nodes of the lower lobe are found medial or lateral to the basilar stem of the lower lobe bronchus.

The anterior mediastinal lymph nodes are in the prevascular compartment of the mediastinum and override the upper portions of the pericardium and great vessels as these extend upward. On the right side, the nodes lie parallel and anterior to the right phrenic nerve. They extend upward to and along the superior vena cava (these may be located between the vein and the ascending aortic arch) to the area beneath the right innominate vein. On the left, they are in close proximity to the origin of the pulmonary artery and the ligamentum arteriosum. They extend upward near the left phrenic nerve to lymph nodes
lying along the inferior border of the left innominate vein in the region where it is joined by the left superior intercostal vein.

The tracheobronchial lymph nodes lie in three groups around the bifurcation of the trachea. The right and left superior tracheobronchial nodes are located in the obtuse angles between the trachea and the corresponding mainstem bronchus. These nodes lie outside of the pretracheal fascia. The lymph nodes of the right superior tracheobronchial group are medial to (beneath) the arch of the azygos vein and above the right pulmonary artery. These nodes are contiguous with the right superior hilar nodes distally and the right paratracheal nodes proximally. On the left side, the superior tracheobronchial nodes lie deep within the concavity of the aortic arch. Some are closely related to the left recurrent laryngeal nerve; others are situated slightly more anteriorly and are contiguous with the node at the ligamentum arteriosum and the root of the left pulmonary artery. Their association with these nodes constitutes the link between the nodes in the visceral compartment and those in the anterior mediastinal lymph node group. Last, the para-aortic nodes lying anterior and lateral to the ascending aorta and the arch are also in the anterior compartment.

The inferior tracheobronchial nodes, more commonly referred to as the subcarinal nodes, lie in the angle of the bifurcation of the trachea (Fig. 6-7). Although these nodes, in contrast to the superior tracheobronchial groups, lie within the pretracheal fascial envelope, they lie outside the relatively dense bronchopericardial membrane. These nodes are contiguous with the hilar nodes on the medial aspect of both the right and left mainstem bronchi. Some of the subcarinal lymph nodes lie more posteriorly in relationship to the tracheal bifurcation and are on the anterior surface of the esophagus and are thus connected with the posterior group of lymph nodes. In addition, Brock and Whytehead⁸ described a low anterior tracheal group lying in front of the lower end of the trachea, which constitutes a bridge between the right superior tracheobronchial lymph nodes and the subcarinal, inferior tracheobronchial lymph nodes.

The paratracheal lymph nodes are situated on the right and left sides of the trachea above the respective superior tracheobronchial nodes and extend upward along the trachea. The right paratracheal lymph nodes lie anterolaterally to the trachea and to the right of the innominate artery. Inferiorly, these nodes are overlapped by the superior vena cava. More superiorly, these nodes lie behind and above the innominate artery to the right of the midline of the trachea and extend to the inlet of the chest. Inferiorly, the left paratracheal nodes lie above the tracheobronchial angle to the left of the midline of the trachea behind the aortic arch. More superiorly, they are situated above the arch but behind the great vessels and extend to the inlet of the chest. The left paratracheal lymph nodes are generally smaller in size and number compared with the right paratracheal lymph nodes.

The posterior mediastinal lymph nodes may be separated into two groups: the paraesophageal nodes and those located in either pulmonary ligament. These posterior nodes are identified less commonly in the superior portion than in the inferior portion of the mediastinum. A paraesophageal node occasionally is found retrotracheally at the level of the arch of the azygos vein. The paraesophageal nodes as a group are more numerous in the inferior portion of the mediastinum and are found more frequently on the left than on the right side. The inferiorly located nodes have connections with the para-aortic nodes beneath the diaphragm. In the pulmonary ligament on either side, usually two or more small lymph nodes may be present. A relatively constant node, and usually the largest, lies in close proximity to the inferior border of the inferior pulmonary vein and is often termed the sentinel node of the pulmonary ligament.

Naruke and associates⁴² suggested the use of an anatomic map with the aforementioned conventional lymph node stations numbered so that the various lymph node stations involved by tumor could be uniformly recorded in patients with lung cancer (Fig. 6-8). This mapping scheme is used by most Japanese surgeons and has been used with minor modifications by the Sloan-Kettering Memorial group and others in North America. The American Joint Committee for Cancer Staging and End Results Reporting (AJC) published a similar map in its 1983 fascicle. The lymph node stations are defined in Table 6-3. The American Thoracic Society (ATS) in a report by Tisi and colleagues,⁶¹ however, noted what they believed to be deficiencies in the commonly accepted specific anatomic definition of each nodal station when determined by mediastinoscopy, mediastinotomy, and computed tomography (CT) examinations of the chest. Although some of the points were minor, a major area of conflict was the recommendation that the hilar stations, the right and left stations 10 of the Naruke and AJC maps, be deleted because of the ambiguity of the radiologic definition of these areas. It was suggested that these areas be redesignated as peribronchial on the left and tracheobronchial on the right and be assigned to the mediastinal compartments, both stations being outside of the pleural reflection. It should be noted that recently Asamura
and coworkers³ presented data supporting the concept that the station 10 nodes rightly belong in the hilar compartment rather than being included in the mediastinal compartment. The ATS suggested the anatomic stations as listed in Table 6-4 and located as represented in Figure 6-9. The ATS map has been adopted by many investigators in North America. The validity of one schema over the other is moot. In reviewing data presented in the literature, however, cognizance of the differences in the method of recording the data must be borne in mind for their proper interpretation.