Mediastinum – Lungs, mediastinum and cardiac valves

00:00 Now, I want to shift your focus to the concept of the mediastinum. Again, the mediastinum is that area between the lungs and the pleural cavities that literally stands in the middle of the thoracic cavity. So, on our next slide, you’ll be able to understand the various boundaries that limit this particular region within our thoracic cavity.

00:28 And the first thing that we need to understand would be the boundaries of the mediastinum.

00:34 And those boundaries will be an anterior boundary, a posterior boundary, a superior boundary, as well as an inferior boundary. The anterior boundary will be the sternum and that is the structure here. The posterior boundary to your mediastinum will be all 12 thoracic vertebrae.

01:00 T1 is here, 2, 3, 4, 5, 6, 7, 8, 9, 10, see a little bit of 11 and then 12 would be just a little bit below this illustration. The superior limit of the mediastinum will run from the sternal angle, this notch, excuse me, the jugular notch that’s right above the sternum and then will extend superiorly to the upper limit of T1. The inferior boundary will be limited by the diaphragm and as it comes around posteriorly, it will dive down to T12. The mediastinum can be divided into various divisions. We have a superior division to our mediastinum. Then we have a larger inferior division, which can be subdivided into smaller parcels. So, we need to understand the boundaries of these divisions and subdivisions. The first, here, is a separation of the superior mediastinum from the inferior mediastinum. Our reference points will be the sternal angle, which is formed at the point where the manubrium articulates with the body of the sternum.

02:34 This will be at the level of the second costal cartilages that are attached, then, to the second ribs. So, we’ll run a line from the sternal angle posteriorly and then that line will intersect between T4 and T5. Everything above is in the superior mediastinum. Anything below is a resident of your inferior mediastinum. Now, again, we can subdivide the inferior mediastinum into an anterior mediastinum, middle mediastinum and a posterior mediastinum.

03:17 The anterior mediastinum is shown here in green and it is an area that is between the sternum, anteriorly, and the pericardium, posteriorly. The posterior mediastinum is shaded here and I’m actually going to kind of go over here to the bronchi that are shown here and throw them into this pink shaded area. This is the posterior mediastinum and it’s located between the more inferior thoracic vertebrae and the pericardium here, posteriorly.

04:01 Everything else, then, is going to be in the middle mediastinum and your major occupant will be the pericardium and its attendant, heart and great vessels.