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The Mediastinum

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0:01

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

0:07

approach to the mediastinum, session one.

0:09

We'll have other sessions on the

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mediastinum with CT and maybe MR as well.

0:15

So, I'm going to introduce the term

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vascular pedicle to you because it's

0:19

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

0:31

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

0:40

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.

1:03

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

1:23

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

2:00

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.

2:40

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.

3:04

Rotation is a huge cause for a wide mediastinum.

3:05

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.

4:00

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?

4:39

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.

5:43

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?

5:57

Well, a lot has changed.

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The imaging technology, the body habitus of

6:01

generalized people, and even the trauma protocol.

6:04

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.

7:01

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?

8:41

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.

8:59

Patient rotated to the right, fell out of

9:01

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.

9:33

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.

9:49

Use the mediastinum as, call

9:51

it the vascular pedicle.

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That will look at intravascular volume.

9:56

Very helpful in ICU imaging.

9:58

Um, compare the density.

10:01

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

10:05

more, that needs an explanation.

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And lastly, you can take

10:08

a look at the aortic arch.

10:10

Is it brighter?

10:11

Is there a mass effect around it?

10:12

That also needs an explanation.

10:14

I implore you to try to avoid

10:16

the term wide mediastinum.

10:17

If you find the mediastinum suspicious,

10:20

say it's an indeterminate mediastinum

10:22

or something along those lines.

10:24

With that, thank you very much.

Report

Description

Faculty

Marc V Gosselin, MD

Professor Diagnostic Radiology

Vision Radiology & Oregon Health & Science University School of Medicine

Tags

X-Ray (Plain Films)

Vascular

Trauma

Mediastinum

Iatrogenic

Chest

Cardiac

CT

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