Two sets of lymphatic vessels drain the lung of lymph. A subpleural lymphatic network collects the lymph from the peripheral lung tissue and drains it along the veins leading toward the hilum. There is a deeper lymphatic system that originates around the bronchi and the bronchioles. The deep system joins the lymphatics around the larger bronchi and pulmonary arteries and they finally enter the mediastinum where they join the bronchomediastinal trunks. The final common pathway for all the lymphatic is via the thoracic duct which enters the left subclavian vein.
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Most of the visible lymph nodes are within the hila and mediastinum. However there are lymph nodes that lie close to the periphery of the lung. These are relatively small measuring approximately 2mm. in diameter. They become larger towards the hila, reaching diameters of between 5 to 10mm.
The mediastinal nodes have been divided into 4 main groups; the superior mediastinal, aortic, inferior mediastinal, and N node are the designated groups. Within these groups there are 14 nodal stations. These 14 stations have been given both names and numbers to aid in the classification and staging of disease.
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Group 3 called “prevascular and retrotracheal nodes” can only be appreciated on the axial images since they are found relatively anterior and posteriorly in the chest.
Superior Mediastinal Nodes
1 Highest Mediastinal Nodes
2 Upper Tracheal Nodes
3 Prevascular and Retrotracheal Nodes
4 Lower Paratracheal Nodes
|32682n01n.800 nodes 1,2,4 Superior mediastinal Nodes 1 Highest Mediastinal Nodes 2 Upper Tracheal Nodes 3 Prevascular and Retrotracheal Nodes 4 Lower Paratracheal Nodes chest mediastinum lymph nodes normal anatomy CTscan Davidoff MD|
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5 Subaortic Nodes (A-P window)
6 Paraaortic Nodes (Ascending Aorta or Phrenic)
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Inferior Mediastinal Nodes
7 Subcarinal Nodes
8 Paraesophageal Nodes
9 Pulmonary Ligament Nodes
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10 Hilar Nodes
11 Interlobar Nodes
12 Lobar Nodes
13 Segmental Nodes
14 Subsegmental Nodes
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|46851c01 lung lymphatics lymph nodes mediastinum hilar and intraparenchymal mediastinal lymphadenopathy aortic nodes paraaortic 6 A-P window 5 Inferior mediastinal subcarinal 7 N Nodes hilum 10 interlobar 11 segmental 13 dx sarcoidosis CTscan Davidoff MD 46842 46843 46843c01|
50-year-old male presents with history of Stage 4 sarcoidosis acute chest pain and dyspnea
The initial CXR shows a left sided pneumothorax, diffuse nodular pattern with confluent perihilar infiltrates and a left pleural effusion
A chest tube was placed and a chest CT showed confluent fibrotic masses in the hilar regions totally surrounding the bronchovascular bundles with encasement of the middle lobe artery. In addition, multiple lymphovascular micronodules are demonstrated. The pulmonary artery measures 32.7mm indicating pulmonary hypertension.
A CXR during this admission shows re-expansion of the pneumothorax. Left lung volume is reduced.
The patient presents 2 years later, again with progressive dyspnea and chest pain and CT PA shows encasement of the airways, right middle lobe pulmonary artery and left lower pulmonary vein by the fibrotic broncho vascular masses, and non-occlusive, subacute pulmonary embolus of the LPA. There are moderate bilateral pleural effusions, calcified lymph nodes, with ongoing pulmonary hypertension with right ventricular enlargement, right atrial enlargement, tricuspid regurgitation and pulmonary hypertension. At this time the patient is intubated.
He again presents 1 month after with chest pain and dyspnea. At this time, he has a tracheostomy. The scout frontal view shows persistent encasement of the left upper lobe bronchus and significant reduction on the volume of the left lung with elevated left hemidiaphragm.
CT PA has similar findings with a large right pleural effusion and unresolved large non occlusive thrombus in the left pulmonary artery.
Knowledge of the anatomy of the secondary lobule is key to the understanding of the subpleural lymphatic system since the lymphatic of this region run in the interlobular septa. The anatomy of the secondary lobule was extensively discussed in part 1 of the lung module. The ability to image the secondary lobule is key to the diagnosis of many of the interstitial lung diseases and it requires high resolution imaging to enable distinction between changes in the interlobular septa changes within the central bronchovascular bundle and changes within the lobule itself. Since the subpleural lymphatics run in the interlobular septa, it becomes our focus when lymphatic disease is evaluated.
Certain diseases have a predilection for the lymphatic system at the subpleural level including sarcoidosis. On the other hand diseases such as lung carcinoma have a predilection for the deep and central nodal system. Since the systems do connect and are both usually involved i is imperative to evaluate both systems.
The polygonal shape of the secondary lobule is a key shape to recognise. These lobules are well formed at the lung apices, lung bases and particularly at the periphery of the lung. The septa are not usually appreciated in healthy lungs, but may be seen in only mildly diseased lungs as well as advanced disease in the lung. Their presence does not necessarily indicate lymphatic disease since the connective tissue of the septa, and the venules are also located within them.
Courtesy Ashley Davidoff MD 31866collage_1
Sarcoid disease and sarcoid nodules specifically, seek out the lymphatics of both the subleral and the deep systems. Thus when nodules or focal changes are identified on the pleural surfaces, including the fissures, interlobular septa, and bronchovascular bundles then sarcoidosis is a prime suspect. Pleural effusions on the other hand are distinctly uncommon in sarcoidosis.(1-4%). In lymphangitic spread of disease, malignant cells get bundled in to the lymphatics causing obstruction and reducing pulmonary capacity. Thickening of the interlobular septa is a characteristic finding in these cases. In anthracosis, lymph nodes and lymphatics get filled with carbon colored soot.
|Distended Peripheral Lymphatics|
|This combination image represents the post mortem finding of the lung in a patient with poorly differentiated squamous cell carcinoma Note the prominent interlobular septa and polygonal shaped secondary lobules (1). The pleural metastasis cause obstruction and distension of the pleural lymphatics as seen in images 2,3,4. Lymphatics are not usually seen but in this instance since they are obstructed, they have become distended with milky white lymph and measure about .05mms .
Courtesy Ashley Davidoff and Jeffrey Peirce A86-215 32315c
|Lymphangitic Spread of Prostate Carcinoma|
|This histological section is from a patient with prostate cancer metastatic to the lymphatics of the lungs – causing lymphangitis obliterans. The first image shows thickened lymphatics which run in the interlobular sept. 2 is the same image with the thickened septa overlaid in a pale green (2). Images 3, and 4 are higher power showing clusters of glandular metastatic deposits in the connective tissue of the septa.
|Sarcoidosis – thickened lymphatics of the interlobular septa|
|This cross sectional series of 3 CT images shows end stage sarcoidosis characterised by marked thickening along the lymphovascular bundles. The first image in the upper left shows marked thickening of the interlobular septa caused by granulomatous changes along the lymphatics. Courtesy Priscilla Slanetz MD. 31866c|
The Deep System
The subpleural and deep system have a final common pathway. The image below shows this connection by demonstrating spread of malignant disease in the interlobular septa, around the bronchi and in an intrapulmonary lymph node.
|Lymphangitic Disease of the Deep Lymphatic Sytem with Extension to the Interlobular Septa, Peribronchial Lymphatics, and Intrapulmonary Node.
|This is a post mortem specimen of a lung with lymphangitic spread of prostate carcinoma. Malignant disease is overlaid in green. Note the rounded mass of lymphadenopathy with linear extensions along the thickened bronchovascular bundles. The fine linear triangular bands peripherally are lymphatics in the secondary lobule congested with tumor.
Courtesy Ashley Davidoff MD. 32199cw
|Calcified intraparenchymal lymph node|
|This patient with Stage III sarcoidosis has a calcified intraparenchymal node in the confluent fibrosis on the right.
Courtesy Ashley Davidoff MD 32001
Size of Nodes
In general , although we often measure the size, and specifically the short axis of the nodes to determine the presence of disease, we understand that this is a fairly inaccurate method with low specificity . A short axis of more than 10mm implies a pathologically involved node. Often the large node may be reactive and may not contain malignant disease. PET scanning has been an important advance to aid in the distinction between reactive and malignant lymphadenopathy.
|Lymph nodes in Sarcoidosis|
|This set of images shows a conglomerate of small nodes in the azygos (upper paratracheal region) as well as a node that is greater than 1 cms in the right hilum.
Courtesy Ashley Davidoff MD. 31646c
|Large Reactive Node – Pathology negative|
|The node in the azygos region is pathologically enlarged but at pathology was shown to be reactive. note the subtle deformity of the azygos region on the CXR
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|Looking at the edges – Disease beyond the chest|
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|Calcified lymph nodes|
|The A-P and lateral view of the chest is from a patient with sarcoidosis showing classical egg shell calcification of the mediastinal nodes and hilar nodes.
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|Eggshell Calcification Intraparenchymal Calcification – Sarcoidosis|
|33472b01.800 chest lung lymph node mediastinum mediastinal intraparenchymal lymph node fx eggshell calcification dx probable sarcoidosis CTscan Davidoff MD|
|42068c03 Courtesy Ashley Davidoff MD medical students code chest enlarged lung lymph node lymphadenopathy lymphoma mediastinum nodule SVC compressed|
Courtesy Ashley Davidoff MD. 32426cl
Elevated Right Main Stem Bronchus and Encasement
Bilateral Lymphangitis Carcinomatosis in a Patient with Adenocarcinoma
references and Links