First published online April 26, 2006
British Journal of Radiology (2006) 79, 922-928
© 2006 British Institute of Radiology
doi: 10.1259/bjr/26411607
CT of thoracic lymph nodes. Part I: anatomy and drainage
T Suwatanapongched, MD1 and
D S Gierada, MD2
1 Department of Radiology, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, 270, Rama VI Road, Rajthevi, Bangkok 10400, Thailand, 2 Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 South Kingshighway Blvd, Campus Box 8131, Saint Louis, Missouri 63110, USA
Correspondence: D S Gierada
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Abstract
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CT is the primary non-invasive technique for the diagnostic evaluation of thoracic lymph nodes. The CT patterns and anatomic location of thoracic lymph node involvement can provide important clues in the diagnosis of many diseases. Part I of the pictorial review illustrates the anatomic location and drainage of thoracic lymph nodes in the chest wall, mediastinum and lungs through examples of pathologic involvement. Part II of the pictorial review focuses on CT patterns of lymph node involvement in various pulmonary and extrapulmonary diseases, differential diagnoses based on CT findings and pitfalls.
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Introduction
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CT is the primary non-invasive technique for the diagnostic evaluation of thoracic lymph nodes. Lymph node abnormalities are depicted by CT as an increase in nodal size and/or number or change in attenuation. Although these findings are non-specific, patterns of thoracic lymph node involvement can provide important clues in the diagnosis of many pulmonary and extrapulmonary diseases. Part I of this pictorial review illustrates the anatomic location and drainage of thoracic lymph nodes in the chest wall, mediastinum and lungs through examples of pathologic involvement. Part II focuses on CT patterns of lymph node involvement in various pulmonary and extrapulmonary diseases.
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Classification of thoracic lymph nodes
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As in other parts of the body, thoracic lymph nodes are named using descriptive terminology according to the blood vessels or visceral structures to which they are most closely related, or by their general anatomic location. Although there are slight differences in the classification of the thoracic nodes [1–5], they can be divided into those of the chest wall and those of the intrathoracic contents. To facilitate accurate pathologic staging and analysis of treatment outcomes in lung cancer, a classification scheme for mediastinal and pulmonary lymph nodes (Figure 1
) has been devised by the American Joint Committee on Cancer (AJCC) and the Union Internationale Contre le Cancer (UICC) [5], based on surgically recognizable anatomic landmarks.
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Figure 1. Revised American Joint Committee on Cancer(AJCC) and the Union Internationale Contre le Cancer (UICC) regional nodal stations for lung cancer staging. (From Mountain CF, Dresler CM. Regional lymph node classification for lung cancer staging. Chest 1997;111:1718–23 [5]. Reprinted with permission). (a) Drawing illustrates mediastinum lymph node stations in the frontal projection. Ao = aortic arch, PA = main pulmonary artery, 1 (red) = highest mediastinal nodes, 2R and 2L (dark blue) = right and left upper paratracheal nodes, 4R and 4L (orange) = right and left lower paratracheal nodes, 7 (blue) = subcarinal nodes, 8 (grey) = para-oesophageal nodes, 9 (brown) = pulmonary ligament nodes, 10R and 10L (yellow) = right and left hilar nodes, 11R and 11L (green) = right and left interlobar nodes, 12R and 12L (pink) = right and left lobar nodes, 13R and 13L (pink) = right and left segmental nodes, 14R and 14L (pink) = right and left subsegmental nodes. (b) Illustration of mediastinum lymph node stations in the left anterior oblique projection. Ao = aortic arch, PA = main pulmonary artery, 3 (pink) = pre-vascular and retrotracheal nodes, 5 (black) = subaortic nodes, 6 (red) = para-aortic nodes.
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Chest wall nodes
The axillary nodes (Figures 2 and 3) receive superficial lymphatic drainage from the upper limbs, breasts and pectoral muscles excluding their medial portions, parietal pleura, and skin and muscles of the trunk above the umbilicus and iliac crest [1, 2]. The lymph flow is directed toward the terminal nodal group in the axillary apices. The efferent vessels from this group unite as the subclavian trunk, which finally drains directly or indirectly into the jugulo-subclavian venous confluence [1, 2, 6]. A few efferents usually reach the supraclavicular nodes, a well-recognized route for the spread of breast cancer [1, 2, 6].
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Figure 2. Enhanced CT scan in a 66-year-old woman with lymphoma showing multiple enlarged bilateral axillary lymph nodes (arrows).
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Figure 3. A 65-year-old man with chronic lymphocytic leukaemia. (a) Enhanced CT scan demonstrates enlarged right axillary nodes (arrowheads) and right interpectoral (Rotter) node (black arrow) lying between pectoralis major (M) and minor (m) muscles. Nodes in the subpectoral and interpectoral regions are included in the axillary nodal group. Also seen are enlarged highest mediastinal nodes (station 1; white arrows) defined by their location cranial to the superior margin of the left brachiocephalic vein, behind and to the right and left sides of the trachea. (b) Enhanced CT scan at the lower level shows bilaterally enlarged axillary nodes (arrowheads), including left subpectoral nodes (open arrow) underneath the left pectoralis minor muscle (m). There are enlarged pre-vascular nodes (station 3A; white arrows), which lie between the superior margin of the left brachiocephalic vein (V) and the superior margin of the aortic arch, and anterior to its large arterial branches; enlarged retrotracheal node (station 3P; black arrow), which lies behind the trachea and above the inferior aspect of azygos vein arch; and enlarged right upper paratracheal nodes (station 2R; wavy arrow), which are located above the superior margin of the aortic arch.
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The internal mammary (internal thoracic or parasternal) nodes (Figure 4) lie at the anterior ends of the intercostal spaces, along the internal mammary (internal thoracic) vessels. They receive lymphatic drainage from the anterior diaphragmatic nodes, anterosuperior portion of the liver, medial part of the breasts, and deeper structures of the anterior chest and upper anterior abdominal wall [2]. Their efferent channels may empty into the right lymphatic duct, the thoracic duct, or the inferior deep cervical nodes [3, 6].
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Figure 4. Enhanced CT scan at the level of the main pulmonary artery in a 55-year-old woman with left breast cancer demonstrating enlarged left internal mammary node (arrow). Note normal right internal mammary vessels (wavy arrow) and a portion of primary cancer in the left breast (asterisk).
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The posterior intercostal nodes (Figures 5 and 6), located near the heads and necks of the posterior ribs, receive lymphatic drainage from the posterolateral intercostal spaces, posterolateral breasts, parietal pleura, vertebrae and spinal muscles [2–4]. The efferent vessels from the upper intercostal spaces end in the thoracic duct on the left, and in one of the lymphatic trunks on the right [2–4]. Those from the lower four to seven intercostal spaces unite to form a common trunk, which empties into the thoracic duct or cisterna chyli [2–4]. The juxtavertebral (pre-vertebral or paravertebral) nodes lie along the anterior and lateral aspects of the vertebral bodies, most numerous from T8 to T12 (Figures 5 and 6) [3, 4]. They communicate with posterior mediastinal lymph nodes [3] and the posterior intercostal nodes, and similarly drain to the right lymphatic duct or thoracic duct [3, 4].
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Figure 5. Enhanced CT scan of a 31-year-old man with lymphoma showing enlarged, necrotic right and left intercostal nodes (white arrows) as well as enlarged left paravertebral (arrowheads) and retrocrural (black arrows) nodes. Note a left pleural effusion (E) with pleural nodules (small white arrows), splenectomy clips and coeliac adenopathy (N). A = aorta.
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Figure 6. Enhanced CT scan in a 69-year-old woman with lymphoma showing enlarged bilateral paravertebral nodes (white arrows), left intercostal node (open arrow) and anterior diaphragmatic nodes (black arrows). Note bilateral pleural effusions (E).
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The diaphragmatic nodes are located on or just above the thoracic surface of the diaphragm and are divided into three groups [2–4, 7]. The anterior (pre-pericardial or cardiophrenic) group (Figure 6
) is located anterior to the pericardium, posterior to the xiphoid process, and in the right and left cardiophrenic fat. This node group receives afferent drainage from the anterior part of the diaphragm and its pleura, and the anterosuperior portion of the liver. They drain to the internal mammary nodes alongside the xiphoid and can provide a route for retrograde spread of breast cancer to the liver, via lymphatics of the rectus abdominis muscle when the upper internal thoracic trunks are blocked [4]. The middle (juxtaphrenic or lateral) (Figure 7) group receives lymph from the central diaphragm and from the convex surface of the liver on the right [2]. The posterior (retrocrural) group (Figure 8), lying behind the diaphragmatic crura and anterior to the spine, receives lymph from the posterior part of the diaphragm and communicates with the posterior mediastinal nodes and para-aortic nodes in the upper abdomen [2, 4]. When diaphragmatic nodes are enlarged, widespread disease in other locations is usually present, so biopsy of these sites is uncommon [7].
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Figure 7. Non-enhanced CT scan in a 28-year-old woman with metastatic papillary serous adenocarcinoma of the ovary revealing enlarged, densely calcified right middle diaphragmatic nodes (arrow), located lateral to the intrathoracic end of the inferior vena cava (V) and near the insertion of the right phrenic nerve.
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Figure 8. CT scan through the upper abdomen in a 45-year-old man with distal oesophageal carcinoma (not shown) revealing enlarged retrocrural lymph nodes (large arrows) and liver metastases (small arrows).
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Mediastinal lymph nodes
Anterior mediastinal group
This group includes the highest mediastinal (station 1, Figures 1 and 3a), pre-vascular (station 3A, Figures 1 and 3b), and para-aortic (station 6, Figures 1 and 9) nodes [2, 3, 5, 8]. They receive afferent vessels from the thymus, thyroid, heart and pericardium, diaphragmatic and mediastinal pleura, and middle diaphragmatic nodes [2, 3]. Their efferent channels join those from the paratracheal, tracheobronchial and internal mammary nodes, to form the right and left bronchomediastinal trunks, which may empty to the right lymphatic duct, the thoracic duct, or open independently into the jugulo-subclavian venous confluence [2, 3].
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Figure 9. Non-enhanced CT scan in the same patient as in Figure 7 revealing enlarged, calcified para-aortic nodes (station 6; arrows), lying anterior and lateral to the aortic arch (A) below its superior margin. Also seen is right lower paratracheal lymphadenopathy (station 4R; open arrow). V = superior vena cava. (From Glazer HS, Molina PL, Siegel MJ, Sagel SS. High-attenuation mediastinal masses on unenhanced CT. AJR Am J Roentgenol 1991;156:45–50 [8]. Reprinted with permission).
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Paratracheal and tracheobronchial groups
These groups receive drainage from most parts of the lungs and bronchi, thoracic trachea, heart and some efferents from the upper para-oesophageal nodes of the posterior mediastinal group [2, 4]. The nodes comprising these groups include the upper (station 2R, 2L, Figures 1 and 3b) and lower (station 4R, 4L, Figures 1, 9 and 10) paratracheal, subaortic (aortopulmonary window, station 5, Figures 1, 11, and 12), retrotracheal (station 3P, Figures 1 and 3b), and subcarinal (station 7, Figures 1 and 12) nodes [2, 3, 5]. The azygos node, located medial to the azygos arch, is included in station 4R [5]. The upper paratracheal nodes link the lower paratracheal and inferior deep cervical nodes [10]. The subcarinal nodes are contiguous with the hilar nodes and drain to the paratracheal nodes, preferentially to the right [11]. Thus, the left lower lobe is the most common primary site for contralateral mediastinal lymph node metastasis in lung cancer.
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Figure 10. Enhanced CT scan in a 73-year-old man with left lower lobe lung cancer (not shown) showing enlarged right lower paratracheal nodes (large arrow) lying medial to the azygos vein (V) and enlarged left lower paratracheal nodes (station 4L; open arrow) lying medial to ligamentum arteriosum (small arrows). Lower paratracheal nodes lie caudal to the top of the aortic arch. (From Sagel SS, Slone RM. Lung. In: Lee JKT, Sagel SS, Stanley RJ, Heiken JP, editors. Computed body tomography with MRI correlation, 3rd edn. Philadelphia, PA: Lippincott-Raven Publishers, 1998:351–454 [9]. Reprinted with permission).
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Figure 11. Enhanced CT scan in a 58-year-old woman with carcinoid tumour showing enhancing subaortic lymphadenopathy (station 5; arrows) within the aortopulmonary window region. This group is located lateral to the ligamentum arteriosum (not seen). Note primary tumour in the left upper lobe (open arrow).
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Figure 12. Enhanced CT scan in a 65-year-old man with diffuse pulmonary lymphangitic carcinomatosis secondary to non-small cell lung cancer (not shown) demonstrating enlarged subcarinal (station 7; curved arrow), para-oesophageal (black arrow), right hilar (station 10R; large white arrows) and left hilar (station 10L; open arrow) nodes. Hilar nodes are outside the mediastinal pleura, below the top of the upper lobe bronchi. Note enlarged subaortic (arrowhead) and para-aortic (small white arrow) nodes. Oe = oesophagus.
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Posterior mediastinal group
The posterior mediastinal nodes are comprised of the para-oesophageal (station 8, Figures 1 and 12) and pulmonary ligament (station 9, Figures 1 and 13) nodes [4, 5]. The para-oesophageal nodes receive afferent vessels from the thoracic oesophagus, posterior pericardium, diaphragm, posterior diaphragmatic nodes and the left hepatic lobe, and are more numerous on the left [2]. The pulmonary ligament nodes receive drainage from the basilar segments of the lower lobes and lower half of the oesophagus [4]. The efferents from the posterior mediastinal nodes communicate with the tracheobronchial group, particularly subcarinal nodes, and drain chiefly into the thoracic duct, but also drain to the subdiaphragmatic para-aortic or coeliac nodes [3, 4].
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Figure 13. Enhanced CT scan in a 65-year-old man with non-small cell lung cancer demonstrating metastasis to left pulmonary ligament node (station 9; curved arrow) from left lower lobe lung cancer (straight arrow). Oe = oesophagus, A = aorta. (From Sagel SS, Slone RM. Lung. In: Lee JKT, Sagel SS, Stanley RJ, Heiken JP, editors. Computed body tomography with MRI correlation, 3rd edn. Philadelphia, USA: Lippincott-Raven Publishers, 1998:351–454 [9]. Reprinted with permission).
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Lymph nodes of the lungs
Lymph nodes are located along the bronchi and can be divided into hilar (station 10R, 10L, Figures 1 and 12) and intrapulmonary nodes [5, 10]. The latter consist of interlobar (station 11R, 11L, Figures 1 and 14), lobar (station 12R, 12L, Figures 1 and 14), segmental (station 13R, 13L, Figures 1, 14 and 15), subsegmental (station 14R, 14L, Figures 1 and 16) and intraparenchymal intrapulmonary (Figure 17) nodes [5, 9, 12]. Most of the lymphatic flow of the lungs is directed toward the interlobar and hilar nodes, which drain into the subcarinal nodes or directly into the lower paratracheal nodes [3, 4, 10, 11].
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Figure 14. Enhanced CT scan in a 29-year-old woman with sarcoidosis demonstrating enlarged right lobar node (station 12R; arrowhead) at the bifurcation of the bronchus intermedius, right segmental node (open arrow) adjacent to the right middle lobe lateral segmental bronchus, and left interlobar nodes (station 11R and 11L; white arrows) between the lingular and left lower lobe superior segmental bronchus. Note enlarged subcarinal nodes (black arrows) and bilateral pulmonary involvement.
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Figure 15. Enhanced CT scan in the same patient as inFigure 12 showing enlarged right and left segmental nodes (station 13R and 13L; large white arrows) lying adjacent to the segmental bronchi (small white arrows) and enlarged para-oesophageal nodes (black arrows).
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Figure 16. Axial CT scan with lung-window setting in a 59-year-old man with myocardial infarction showing a 1 cm, indeterminate, solitary pulmonary nodule containing an eccentric calcific focus in the right middle lobe (arrow). Wedge resection revealed a subsegmental lymph node (station 14R) with calcified granuloma.
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Figure 17. A 58-year-old man with bronchioloalveolar carcinoma of the left upper lobe (not shown). (a) CT scan with lung-window setting demonstrates a tiny, subpleural nodule in the lingular segment (arrow). (b) Histological examination reveals a normal lymph node (arrows), surrounded by alveolar tissue. It had capsule with visible germinal centres and contains histiocytes and carbon pigment (haematoxylin and eosin x40).
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The normal hilar and interlobar nodes are frequently visible, particularly with thinner (1–3 mm) collimation and intravenous contrast administration [13]. Recognition of these nodes is important to avoid misdiagnosis of pulmonary embolism. Intraparenchymal intrapulmonary nodes may present as indeterminate subpleural pulmonary nodules in the lower parts of the lungs [12].
Received for publication April 11, 2005.
Revision received June 23, 2005.
Accepted for publication July 11, 2005.
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Abstract
Introduction
