Interactive Transcript
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Alright, well cardiopulmonary imaging,
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we're going to do a session on the mediastinum,
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and this is going to be the radiographic
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approach to the mediastinum, session one.
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We'll have other sessions on the
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mediastinum with CT and maybe MR as well.
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So, I'm going to introduce the term
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vascular pedicle to you because it's
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something that I find very useful.
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It reflects intravascular fluid physiologically.
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I'm going to try to introduce also the concept
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of density and contour rather than width.
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I'm going to give you the four most
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common causes for wide mediastinum.
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None of them pathologic.
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And I'm going to emphasize to you and
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plead to you not to use the term wide
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mediastinum on any of your reports.
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It causes anxiety and that's
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not what we are about.
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Okay.
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So let's take a look.
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Normal anatomy.
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This is the vascular pedicle, by the way,
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it is the superior vena cava into the right
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atrium, superior vena cava, and your aortic arch.
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Please know.
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Research has shown there is no knob in the chest.
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So do not say aortic knob.
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It, uh, it's really a low brow.
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It's an arch.
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So the arch measured here to the superior
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vena cava, that is your vascular pedicle.
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And your superior vena cava is very compliant and
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it changes with your intravascular fluid volume.
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So as we go through this, you're going
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to hear a lot of different things.
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So just, he who joyfully marches to music and
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rank and file has already earned my contempt.
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He has been given a large brain by mistake since
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for him, the spinal cord would have sufficed.
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So let's, let's do a little brain thinking here.
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The dogma, wide mediastinum.
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In the trauma setting, that's the means,
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eh, there might be a hematoma, which may
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mean it could be a great vessel injury.
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So these are indirect signs.
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When you use the term wide mediastinum,
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clinicians get anxious, and when they
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get anxious, they start ordering things.
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So what about this concept?
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A wide mediastinum in the trauma
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patient is actually a good prognosis.
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Well, let's look into that.
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What is the mediastinum width
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again, the vascular pedicle?
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What does that reflect?
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Intravascular fluid volume.
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You have a trauma patient who's laid out supine.
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With increased flow from the legs, IV
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pumping in normal saline or Ringer's
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lactate or whatever their choice is.
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Man, you better have a wide mediastinum,
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a wide vascular pedicle.
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If it's narrow, what does that suggest?
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They're bleeding out some.
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So it's, it's, seeing a wide vascular
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pedicle in the setting of trauma
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is not necessarily a bad thing.
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It's probably physiologically a good thing.
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Okay, you can use the vascular pedicle or the
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mediastinal width if you wish, but vascular
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pedicle when you're looking at ICU patients.
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Notice it's wider here in a patient with
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pulmonary edema, congestive heart failure.
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After diuretics, and what does a diuretic do?
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It decreases the intravascular volume, your
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mediastinum or vascular pedicle gets smaller,
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and the fluid gets reabsorbed, and it's gone.
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Rotation is a huge cause for a wide mediastinum.
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82 00:03:08,220 --> 00:03:09,170 What do I mean by that?
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You look at your clavicles
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medially and the spinous process.
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When you are rotated to the right, your superior
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vena cava, which forms that right border, is then
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thrown out far and the descending thoracic aorta,
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which forms the left, is actually also thrown out.
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So you actually widen it out.
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What do I mean by this?
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You look at this patient who's rotated to the
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right, and you can see it's a wide mediastinum.
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But that's the same person just a few
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minutes later, we just did this because we
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were bored, um, we threw someone on there,
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and it narrowed the mediastinum when you
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rotate to the left because you overlap them.
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So rotation to the right will widen the
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mediastinum. But that's not pathologic.
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A tortuous thoracic aorta.
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What do you, why does it get tortuous
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or why does it unfold with age?
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And no, it has nothing to do with hypertension.
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It has nothing to do with compliance.
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It has nothing to do with all of these
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other things that people make up.
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It is simply the fact that you
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lose height as you get older.
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You get kyphotic, lose height in your
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vertebral bodies, and then as the
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roof comes down, the aorta bulges out.
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That's as simple as that.
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But when it bulges out,
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it can widen the mediastinum.
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Lastly, mediastinal ligamentosis.
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Body habitus has changed these days, people.
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It's not the same as when I was a kid,
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and I'm not lecturing, just observing.
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And mediastinal fat is now commonly
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seen, and it widens the mediastinum.
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So, what does a wide mediastinum mean?
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It means the vascular pedicle or
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intravascular fluid volume is increased.
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It means there is mediastinal fat.
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It means the person is rotated to the right.
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Um, or there's a tortuous aorta or some combination.
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None of those are pathologic.
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So, and, and Ho and all did a study at
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Harborview and they looked with six blinded
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radiologists at 30 trauma and 47 randomly.
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And they only two criteria, one,
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just your gestalt overall impression.
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And two was the mediastinum wide.
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Was it wide?
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And look what the results were.
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They actually did much worse on trying
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to figure out if the mediastinum was
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even wide with a greater interobserver
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variability of, uh, or lower inter or
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increased interobserver variability.
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So it is not a good sign anyway.
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And when you use it, you make people
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nervous and, uh, they think, and I agree,
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medical education has ingrained the widely
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promoted concept that mediastinum widening,
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which is misleading and that we believe the
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term causes confusion and should be avoided.
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Concur.
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What is a wide mediastinum?
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It actually comes from 1976, concluded
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that eight centimeters are greater than 25
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percent of the thoracic cavity is abnormal.
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And it was a really good study back then.
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What has changed since 1976?
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Well, a lot has changed.
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The imaging technology, the body habitus of
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generalized people, and even the trauma protocol.
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Okay, so the old films, the narrow
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latitude, black lungs, white mediastinal
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blob, what criteria could we use?
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Contour and width.
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Nowadays, the, the, the latitude is much wider.
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We see the different densities
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within the mediastinum.
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We can appreciate that, but we haven't
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incorporated that in our teaching or
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curriculum or in a way we approach our imaging.
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So what do we do?
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One, wide mediastinums are going to be
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common in these trauma patients, mainly
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because one, we're doing it differently.
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In the old days, we used to put the
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film screen right behind the patient,
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they barrel roll and put them up.
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Nowadays, we put the screen in the table.
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So the patient to screen distance
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is increased quite a bit.
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We studied this at OHSU and we got about a 17
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to 25 percent magnification of the mediastinum.
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So this is what I would suggest.
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Look at the density and contour,
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ignore whether it's wide or not.
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The aortic arch is your standard of reference.
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That's your reference.
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Look at the right side of the
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trachea, the superior vena cava.
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Is it the same density or is it less dense?
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That's normal.
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Is it the same density or higher?
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That needs an explanation.
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Okay, this is normal.
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There's your arch.
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There's your superior vena cava your vascular
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pedicle Notice the arch will always be brighter
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and more pacified because it's horizontal and that
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superimposes the blood The superior vena cava is
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vertical blood with air and fat on both sides.
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So it should always be less It's
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opaque than the aortic arch.
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What about this one?
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It's not a wide mediastinum,
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but this density is too high.
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It's greater than the aortic arch.
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There's mass effect on the trachea.
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This is blood.
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This is abnormal.
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How about this?
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Can't see the arch.
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The right side has contours that are
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convex and it's brighter than the arch.
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This is, this is abnormal.
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If this is trauma, this is blood.
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If it's an outpatient, this is adenopathy.
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And then lastly.
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It could still be normal,
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but you can't see the arch.
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It's completely dense.
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Uh, there's mass effect on the NG
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tube, the esophagus and the trachea.
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This is a contained rupture or
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a large mass in the mediastinum.
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So, let's take you through it real fast.
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Trauma patient.
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What are, are we worried about the mediastinum?
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Yes.
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Density is too high.
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It's convex.
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Can't see the arch.
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That's blood, blood, and blood.
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This person, trauma, wide mediastinum.
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I don't care.
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The arch is here, but there's lots of fat.
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I see the azigous vein.
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There's no mass effect in the trachea, normal.
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Patient rotated to the right, fell out of
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her chair, CT because of a wide mediastinum.
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It's a tortuous aorta, rotated to the
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right, normal density on the right.
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You see the azigous arch.
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There's nothing pathologic here.
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Don't even send them a CT.
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Look at the mass effect on the trachea.
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Look at the convexity of the AP recess.
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The aorta is bright.
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Can't even see it.
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This is great vessel injury, period.
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This person, what do you think?
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Narrow mediastinum, not a good sign.
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They were bleeding out, by the way, quite a bit.
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And notice the right side of the mediastinum.
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It's the same density as the arch.
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There was actually a mediastinal hematoma here
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from a burst fracture in the upper thoracic spine.
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So, um, summary.
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Use the mediastinum as, call
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it the vascular pedicle.
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That will look at intravascular volume.
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Very helpful in ICU imaging.
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Um, compare the density.
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Look at the aortic arch.
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What's the right side?
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If it's the same density or
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more, that needs an explanation.
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And lastly, you can take
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a look at the aortic arch.
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Is it brighter?
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Is there a mass effect around it?
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That also needs an explanation.
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I implore you to try to avoid
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the term wide mediastinum.
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If you find the mediastinum suspicious,
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say it's an indeterminate mediastinum
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or something along those lines.
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With that, thank you very much.
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