Hi, welcome back, I'm Leslie Quint, from the Radiology department at Michigan, and today I'll be talking about the Regional Lymph Node Staging Classification system for lung cancer. Let's start out with the pre-lecture question. The regional lymph node mapping scheme for lung cancer directly enables which of the following? Reliable survival curve generation. Optimal treatment option decisions. Dependable prognostic assessments. Or consistent lymph node designations. Please pick your one best choice, and we'll get back to the question, at the end of the lecture. Okay, well let's start out with an introduction. The optimal treatment and prognostication for our patients with lung cancer, depends upon accurately staging the disease. In order to accurately stage the disease, it's very helpful to use a common terminology for lymph node stations, which helps us to achieve consistent staging assessments. The common terminology that we currently use, is lymph node mapping scheme of the International Association for the Study of Lung Cancer, which is abbreviated IASLC. The objectives for this talk are first of all, to review the definitions of regional lymph node stations in the IASLC staging classification system. And secondly, to illustrate these stations with examples on CT scans. Here are two diagrams that show the lymph node stations. This looks rather complicated and somewhat overwhelming but don't despair we'll go through the stations one by one. So let's start out with Lymph Node Station #1. These are the lymph nodes that are in the low cervical, supraclavicular, and sternal notch regions, as we see on this diagram. These lymph nodes are below the lower margin of the cricoid cartilage, and they're above the level of the clavicles and the manubrium. And here is an example of lymph nodes in Station #1 in the supraclavicular region. Let's move on down to Station #2. These are the upper paratracheal lymph nodes and we'll start with the right sided nodes, in other words Station 2R. These lymph nodes are below the lung apex and below Station #1, and they are above the level of the innominate vein and the aortic arch as we see in this diagram. Notice that's station 2R extends over to the left lateral border of the trachea. So lymph nodes that are anterior to the trachea are classified as right sided lymph nodes. It's only when the lymph nodes move off to the left side of the lateral tracheal margin as we see here, that we call these left sided lymph nodes. So this would be station 2L. Here's an example of a 2R lymph node, in other words in the right upper paratracheal region. Let's move on now to Station #3a. These are the prevascular lymph nodes. They are below the level of the lung apex and above the carina and they are posterior to the sternum. As we see in this diagram, the lymph nodes are anterior to the superior vena cava and they are also anterior to the left common carotid artery. Here is an example of a Station 3a, a pre-vascular lymph node behind the sternum. What about Station 3p? These are the retrotracheal lymph nodes, they are below the level of the lung apex and above the carina. And here's an example of a Station 3p retrotracheal lymph node. Let's now move on to Station 4. And we'll start with the right sided nodes, Station 4R. These are the right lower paratracheal and pretracheal lymph nodes. They are below the level of the innominate vein and above the level of the azygous arch. And here we see these lymph nodes as we're looking through the aortic arch. Just as Station 2R extends over to the left lateral border of the trachea, also Station 4R extends over to the left lateral border of the trachea. So lymph nodes that are anterior to the trachea are considered right sided lymph nodes. And here is an example of a 4R lymph node in the right lower paratracheal region. 4L lymph nodes are those which are off beyond the left lateral border of the trachea as we see in this diagram looking through the aortic arch. These lymph nodes are medial to the ligamentum arteriosum, and this small rectangle here indicates the ligamentum arteriosum. Station 4L is below the upper margin of the aortic arch and above the top of the left main pulmonary artery. Alright, let's now talk about Station 4L, these are the lymph nodes in the left lower paratracheal region and these lymph nodes are medial to the ligamentum arteriosum. On this image we can see the assicus arches here, here is the esophagus and this is lymph node in Station 4L. That brings us to Station #5, the subaortic, or aorto-pulmonary window region. These lymph nodes are lateral to the ligamentum arteriosum. In this diagram, this rectangle is the ligamentum arteriosum and here are the lymph nodes, in Station #5. These lymph nodes are below the bottom of the aortic arch and above the top of the left main pulmonary artery. In this CT image we see this lymph node which is in Station 5, that is an AP window lymph node. The ligamentum arteriosum is somewhere in this region, and this small lymph node is a Station 4L lymph node. So why am I making this distinction about 4L lymph nodes, which are medial to the ligamentum arteriosum and Station 5 lymph nodes, which are lateral to the ligamentum arteriosum? Well, that has important implications, one of which is how we would access these lymph nodes if we wanted to obtain a tissue sample. So a 4L lymph node could potentially be sampled with mediastinoscopy, or an EBUS procedure through the trachea. Whereas, we cannot get to a Station 5 lymph node with those techniques. To sample this lymph node we would need to think about perhaps a VATS procedure or a Chamberlain procedure. So it is often important to distinguish between Station 4L and Station 5. That brings us down to Station #6. These are the anterior para-aortic lymph nodes. As we see in this diagram, these lymph nodes are anterior and lateral to the ascending aorta and the aortic arch. They are below the top of the aortic arch, and above the bottom of the aortic arch. And here is an example of a patient with two lymph nodes in Station 6 anterior para-aortic. Moving on down now to Station #7. This is an easy one to remember, these are the subcarinal lymph nodes. So these lymph nodes are located below the carina, above the left lower low bronchus on the left side and above the lower border of the bronchus intermedius on the right side. And here's an example of a Station 7 lymph node in the subcarinal region. Moving down to Station #8. This one is also easy to remember, these are the paraesophageal lymph nodes. So these lymph nodes are located below the level of the carina and adjacent to the esophagus as we see in this diagram. These lymph nodes are below Station #7, and above the level of the diaphragm. And in this CT, we see two Station 8 lymph nodes. One here, and one here, very close to the esophagus. So again, these are the paraesophageal lymph nodes. I'm going to skip over Station 9, those are the inferior pulmonary ligament lymph nodes. I'm skipping them because we generally do not see them on CT scanning and we'll move right on to Station #10. Everything that we've looked at so far is generally considered to be a mediastinal lymph node, once we get to Station 10 we're talking about hilar lymph nodes. So Station 10 includes lymph nodes below the level of the azygous arch on the right and below the top of the left pulmonary artery on the left, as we see here on the diagram. Station 10 is above the interlobar region bilaterally. Here's a patient who has a right lower lobe lung cancer, and there's a lymph node here in the right hilum, this is a Station 10 lymph node. Moving on to Station #11. These are the interlobar lymph nodes they are between the origins of the lobar bronchi. So here 11R on the right and here 11L on the left. And here's a patient who has a cavitary right lower lobe lung cancer and a prominent lymph node here in Station #11, interlobar. I will not be going over Stations 12, 13, and 14, those lymph nodes are simply further out along the bronchial branches. We generally cannot distinguish among Stations 11, 12, 13, and 14 on our CT scans and clinically that distinction is often irrelevant. Okay, so we've gone through with CT examples and with words where all these lymph node stations are. Sometimes however in clinical practice, you'll look at a scan and you'll have a little trouble figuring out what station you're dealing with. This is a nice resource that you can refer to. This is an article by Dr. Lynch and colleagues on Practical Radiation Oncology. And what these authors have done is taken a series of CT slices, and on each slice they have outlined the various different lymph node regions and labeled them. So this can be very helpful when you're trying to figure out a station in an individual patient. Another nice resource that's in the literature is this article in radiographics from Dr. El-Sherief and colleagues. There are some very nice diagrams showing the lymph nodes stations. But even better what they do for us is they help us distinguish neck lymph nodes or Station 1 from mediastinal lymph nodes, Stations 2, 3 and perhaps even 4. And what they tell us to do is to find the plane of the first rib. And any lymph nodes that are above that plane are considered in the neck, or Station 1, and any lymph nodes below that plane are considered to be mediastinal lymph nodes. These diagrams are taken from a manuscript that came out of the IASLC Lung Cancer Staging Project. And what we see here are proposed groupings of lymph node stations. So region number one is in the superclavicular zone. And here you can see they have proposed that we group Stations 2, 3, and 4, into an upper lymph node zone, or superior mediastinal lymph nodes. Stations 5 and 6 can be grouped into the aortal pulmonary zone or aortic node. And then we have the inferior mediastinal lymph nodes, Stations 7, 8, and 9. And then we move on to the N1 lymph nodes, these are Stations 10 through 14. Generally, these stations are considered to be the N2 or N3 lymph nodes depending on the side of the primary tumor, whereas these lymph nodes are felt to be N1 lymph nodes. Well that brings us to our post-lecture question. The regional lymph node mapping scheme for lung cancer directly enables which of the following? Reliable survival curve generation. Optimal treatment option decisions. Dependable prognostic assessments. Or consistent lymph node designations. And the best answer here would be consistent lymph node designations. The mapping scheme helps with the first three features but it doesn't directly enable those features. So that brings us to our take home points. The use of common terminology for lymph node stations directly enables optimal communication of imaging and surgical findings. And that leads to enhancement in consistency and reliability of clinical staging. And with that I thank you very much for listening and I look forward to seeing you again.
