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.

 

Subpleural Lymphatic Network Interlobular Septa containing Lymphatics and Venules at the Pleural Surface

Normal lung histology This image of the lung periphery shows secondary lobules and interlobular septa. Within the interalveolar septae, one sees small venules and lymphatics.Courtesy Armando Fraire MD. 32649b

Secondary Lobule – Lymphatics and Venules Travelling Together

The arteries and airways pair up and travel together from the interlobular septa to the hilum.   The pulmonary lobule, also called the secondary lobule is a structural unit surrounded by a membrane of connective tissue, and it is smaller than a subsegment of lung but larger than an acinus. This diagram shows two secondary lobules lying side by side. The pulmonary arteriole (royal blue) and bronchiole (pink) are shown together in the centre of the lobule (“centrilobular”), while the oxygenated pulmonary venules (red) and lymphatics (yellow) are peripheral and also form a formidable and almost inseparable pair. Courtesy Ashley Davidoff MD 42440b01

Heart Failure Kerley B lines

In these images. and c are normal and b and d represent thickened interlobular septa in a patient with congestive heart failure.  These are the well known Kerley lines, often spoken about but rarely seen.  They are identified as thin horizontal lines usually seen in the costophrenic angles, not being longer than 2 cms in length and touching the pleural surface.  42545c01.800 Davidoff MD

 

Heart Failure with Lymphatic Congestion Kerley A, B , C lines

There is severe congestive cardiac failure in this CXR with evidence of Kerley B lines seen as horizontal thin lines touching the pleura in the right costophrenic angle in a, and the presence of 3 thin lines coursing obliquely toward the hilum in image b,  representing distended lymphatics running with the bronchovascular bundles.  These lines are called Kerley A lines and they are quite rare. Kerley C lines represent the reticular pattern of intraparenchymal lymphatics which in this case are quite vague. 46424c01 Davidoff MD

Pleural and Fissural Involvement in Sarcoidosis

46843c01 lung pleura fissures lymphatics interstitium interstitial disease fx nodules dx sarcoidosis CTscan Davidoff MD 46842 46843 46843c01 46846 46847 46848 46849 46851

 

Lymph Nodes

 

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.

 

The Mediastinal Nodes

32682n04.801 lung chest mediastinum lymph nodes anatomy normal CTscan Davidoff MD

 

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

 

Superior Mediastinal Nodes 1= Highest, 2= Upper Tracheal and 4 = Lower Paratracheal

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

Superior Mediastinal Nodes 3 = Prevascular Nodes

This patient has lymphoma and the nodal groups of the mediastinum are all enlarged. 42058c01  Davidoff MD

Superior Mediastinal Nodes 3 = Prevascular  4 = Lower Paratracheal Aortic Nodes 6= Paraaortic Nodes

42058c02  Davidoff MD

Aortic Nodes

 

5 Subaortic Nodes (A-P window)

6 Paraaortic Nodes (Ascending Aorta or Phrenic)

 

Aortic Nodes 5= A-P window and 6= Paraaortic

32682n07n.800  Davidoff MD

Aortic Nodes  6= paraaortic Superior Mediastinal 3 – Prevascular Nodes     4 = Lower Paratracheal

42059c01 Davidoff MD

 

Inferior Mediastinal Nodes

 

7 Subcarinal Nodes

8 Paraesophageal Nodes

9 Pulmonary Ligament Nodes

 

Inferior Mediastinal Nodes 7= Subcarinal,  8= Paraesophageal and 9= Pulmonary Ligament

32682n06n.800 Davidoff MD

N Nodes

 

10 Hilar Nodes

11 Interlobar Nodes

12 Lobar Nodes

13 Segmental Nodes

14 Subsegmental Nodes

 

N Nodes 10=Hilar, 11=”Interlobar,” 12=”Lobar,” 13=”Segmental,” 14 = Subsegmental

32682n05ns.800  Davidoff MD

Mediastinal Hilar and Intraparenchymal Disease in Sarcoidosis

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

A Patient with Sarcoidosis with Calcified Nodes at Many Stations

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.

See Radiographics

Applied Anatomy

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.

 

 

 

Subpleural System

 

 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.

 

The polygonal shape of the secondary lobule can be seen all around you when you start looking

This is a series of images demonstrating the shape of the secondary lobule. The first image (1) is a post mortem specimen with congested lungs showing the interlobular septa, while the next (2), is an overlay of the septa in white showing their polygonal shape. The next drawing reveals side-by-side secondary lobules with central bronchovascular bundles and peripheral lymphovascular bundles. Image 4 is a CT image through the apex of the lung showing thickened secondary lobules in a patient with mild emphysema, and 5 shows marked thickening of the interlobular septa in a patient with end stage sarcoidosis. 6,7,8 show the shape of the secondary lobules in the skin of a giraffe, the bark of a pine, and the ripples of the water respectively. 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. 32226c1

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

Mediastinal Nodes

 

 

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 33080.800 Davidoff MD

Looking at the edges – Disease beyond the chest

32991b.800 lung chest mediastinum axilla lymph node lymphadenopathy fx enlarged numerous round dx lymphoma

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. Courtesy Ashley Davidoff MD 42195c01

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

Calcified Metastatic Colon Carcinoma

45137 elderly female with known sigmoid colon carcinoma liver lungs mediastinum hilar lymph nodes in right hilum fx calcified metastases fx calcifications A-P window node fx mediastinal lymphadenopathy Note that the CTscan was performed 2 years after the PET dx colonic mucinous adenocarcinoma with metastatic disease to the liver, mediastinal lymph nodes and lungs CTscan Courtesy Ashley Davidoff MD 45132 45133 45134 45135 45136 45139 45141

Extensive Mediastinal Lymphoma and Lung Nodule

42068c03 Courtesy Ashley Davidoff MD medical students code chest enlarged lung lymph node lymphadenopathy lymphoma mediastinum nodule SVC compressed

Small Cell Carcinoma

This collage of CT and plain film represents the radiological history of a patient with poorly differentiated small cell carcinoma, with extensive parenchymal involvement of the RUL and RML, and of the airways of RML and RLL. Images 1 and 2 show an interstitial and pneumonic pattern which was persistent over time. The CT shows extensive endobronchial disease involving right main stem (3,4) as well as almost all segments of RLL with extensive hilar and mediastinal adenopathy. This was confirmed by bronchoscopy.  Surprisingly little volume loss has occurred. Lymphangitic disease seems to be the dominant finding in the RUL on the lung windows. (5) Following stent placement through a “pinhole” lesion, the patient occluded the RUL airways with tracheal shift and hyperinflation of the left lung (6,7,8,9). Clinically however, she improved greatly. Courtesy Ashley Davidoff MD. 32426cl

Elevated Right Main Stem Bronchus and Encasement

Bilateral Lymphangitis Carcinomatosis in a Patient with Adenocarcinoma

 

references and Links

 

Cases

044Lu Chronic Inactive TB  Lymphatic Distribution