So now let?s discuss pulmonary embolism.
This is a relatively common finding
that?s seen in patients presenting with chest pain.
This represents thrombi that travel to the pulmonary arteries
from other parts of the body. They can be of any size
and they can be located within any of the pulmonary artery branches,
a common location for them to travel
from is the deep venous system of the lower legs.
So if a patient has what?s called a DVT or a Deep Venous Thrombosis
in the lower legs, they should be scanned for a pulmonary embolism
because it?s very common for these DVT?s to travel up to the lungs.
So, let?s take a look at this radiograph.
We see what it looks like an area of consolidation in the right lower lobe.
So this is an example of what?s called a Hampton?s hump
which is a peripheral wedge shaped opacity
that actually indicates pulmonary infarction.
However, radiography is actually very limited
in terms of it?s sensitivity in detecting pulmonary embolism.
You can have pleural effusions,
you can have what?s called the Westermark sign
which is a radiolucency distal to the obstructed pulmonary artery
but these are all very vague findings and nothing really definitive
to help you diagnose a PE. CT is really the modality of choice
and it really has to be performed with contrast.
It can demonstrate a filling defect within the pulmonary artery,
so as you can see here, you have filling defects
within the right sided pulmonary arteries in the patient
that had that chest x-ray. And this is the area of consolidation
that we saw on the chest x-ray which represents a pulmonary infarction.
But if a patient can?t have contrast, if the patient again,
has renal failure or has a contrast allergy,
an alternative is a ventilation/perfusion scan or a VQ scan,
and this is the type of nuclear medicine scan
that compares the ventilation and perfusion images throughout the lungs
and it shows you areas of abnormal perfusion or mismatch.
So you can see here, the top two images
demonstrate normal ventilation and the bottom two images
demonstrate perfusion which has an area of a defect
in the lower lung on the right. So this represents a mismatch
and this is an example of a pulmonary embolism.
Pulmonary Artery Hypertension is not very commonly seen
but when you do see it, it?s important to identify it.
It can be primary or secondary,
so secondary causes include mitral stenosis, recurrent PE, CHF,
or it can be caused by emphysema or fibrosis,
any type of chronic lung disease,
and it results in pruning or dilatation of the central pulmonary artery
with very small peripheral vessels.
So you can see this example on this radiograph
where the central pulmonary artery near the hilum
is quite enlarged and then you have kind of a radiolucency
in the peripheral aspects of the lungs
because the pulmonary vessels are much smaller than would be expected.
This is an example demonstrating pulmonary artery hypertension
versus the normal and you can see the difference in the two,
so again, you can see there?s prominence of the pulmonary artery
on the right which looks much more prominent
than it does in the normal chest x-ray.
The normal chest x-ray demonstrates sort of a grey-ish appearance
to the lungs while in a patient with pulmonary artery hypertension,
you actually have a blacker appearance to the lungs again,
because of lack of peripheral blood vessels.
So in pulmonary artery hypertension,
you have dilatation again of the central pulmonary vasculature.
A normal main pulmonary artery is about the same size
as the ascending aorta but in hypertension, because of the dilatation,
you actually have an enlarged pulmonary artery
and it?s larger than the ascending aorta
or larger than about three centimeters in size,
and that?s what helps you identify this on a CT scan.
So in this lecture, we?ve reviewed thoracic aortic dissection,
thoracic aortic aneurysm, pulmonary embolism,
and pulmonary artery hypertension.
Again, a lot of these findings associated with the great vessels
can be life threatening and really should be detected
as quickly as possible, and as we mentioned,
a CT scan with contrast is really the modality of choice.