Welcome to this overview on the thoracic viscera.
Our purpose here is to provide you major take-home
messages and to avoid excessive detail within
this particular lecture.
This slide lists the objectives that you should
be able to answer at the conclusion of this
First, list the three major compartments of
the thoracic cavity.
Describe the topography of the lungs.
Describe the boundaries and divisions of the
List the major viscera or organs located in
each of the divisions of the mediastinum.
Describe the surface topography for the auscultation
of cardiac valves.
Describe the general function of the thymus
gland and its mediastinal location.
Then we’ll summarise the key take-home messages
and then provide attribution for the images
that were used throughout this lecture.
Here is our body map and our focus will be
anteriorly, approximately in this area of
our body map. And then posteriorly, our focus
will be generally deep to the area within
This slide is an illustration that demonstrates
the three major compartments that exist within
the thoracic cavity. Two of these compartments
are pleural cavities. The right pleural cavity
is shown here. It harbors the right lung,
so that would be its resident. Here, on the
left side, we see the left pleural cavity
and its occupant will be the left lung.
Between our two pleural cavities, we have
this area standing in the middle of the thoracic
cavity. This is the mediastinum. Also of note
is the fact that we have a nice cardiac or
heart window right in through here. And part
of that window is provided by the fact that
the left lung gets displaced toward the left
side of the thoracic cavity, towards its own
pleural cavity, and there’s a notch created
by the impression of the heart. This allows
access to the heart, if an intracardiac injection
needs to be administered. It also provides
access to the heart, if there’s fluid accumulating
within its pericardial cavity and that fluid
has to be withdrawn.
Here, we’re looking at a radiograph of the
thoracic cavity and we can see the two pleural
cavities as well as the mediastinum standing
in the middle. The pleural cavities are going
to appear relatively black. The mediastinum
is going to have a much lighter appearance
in its contrast. So, here is our right pleural
cavity and we can see how dark it is.
We can also see here, on the left side, the
left pleural cavity, and again, we can see
how dark it is. And the darkness is due to
the fact that the lungs hold a lot of air
and the x-ray beam will readily pass through
any air-filled structures, thereby darkening
the film and providing for this nice, dark
We can also visualise, though it’s obscured
by the vertebrae, but we can also visualise
the air-filled trachea. So, if you look here,
between this vertebra and the vertebra below,
you can see how darker it is. You can also
see some blackness imparted here between those
two vertebrae and even up here more superiorly,
you can see some areas of darkness between
the bony vertebrae. This would be the air
that is filling the trachea.
The mediastinum, then, would be represented
by the lighter areas that we see in through
here. The major occupant within this portion
of the mediastinum is the heart and so, we
can see a nice cardiac silhouette. Here’s
the left ventricle over in through here and
if we come over here, we can see the right
atrium bulging toward the right side of the
Here is a cross-section or axial section through
the thoracic cavity. The plane of section
is right along here, where you see the red
line and it’s very, very important that this
axial section is oriented as such that you’re
standing at the feet of the individual, looking
upwards toward the individual’s head. That
means that the left side of the image is,
then, the right side of the individual and
the right side of the image is the left side
of the individual.
So, if we go back here, here is your right
lung within the right pleural cavity. Here
is the left lung, that’s a resident of your
left pleural cavity. And then here, we can
see the pericardium of the heart in green
and we can see the heart muscle itself. The
portion outlined here is your left ventricle.
So, the heart and its pericardium lie within
the mediastinum. Let’s now apply the illustration
that we saw here to radiologic imaging.
All right. Let’s now take a look at the thoracic
cavity as viewed with CT and we are looking
at an axial section through the thoracic cavity.
And again, keep in mind what appears dark
versus what appears bright and the most obvious
dark areas are these huge regions right in
through here. This would represent air in
a lung and since this is the left side of
the image, this is the patient’s right lung.
We also have a large area that’s dark on this
side of the image, which would be the patient’s
And then we see some areas that are bright.
This area represents blood flow. The blood
is flowing through your ascending aorta. It
is coming towards us as we view this image.
The ascending aorta would go into the arch
and then the arch will curve to the left posteriorly
and will pick that descending portion of the
aorta up along the left side of the vertebral
column. And again, it appears bright because
of the blood that’s flowing through it.
We also have, in this area, a bright spot,
again, representing blood flow. This is blood
flowing through the superior vena cava and
it’s going to empty into the right atrium.
And if we look within the substances of the
lung, we can see these bright areas that have
a branching pattern. We see the same kind
of bright branching pattern within the left
lung and since these are bright areas that
have branching, these branching patterns represent
blood flow into the lungs.
And then, if we take a look here and here,
we see two luminous profiles and the lumen
of each one of these profiles is dark. That,
by interpretation, means that these structures
have air within them and these, then, will
represent the bronchi. The substance of each
lung has these bright networks within them.
And they’re a little bit brighter here, perhaps,
on the right side of the image within the
left lung. And again, these bright streaks
or networks represent blood.