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