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Hey everybody, it's Mark again.

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We're gonna talk today a little bit about reticular opacities

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as we continue on the whole curriculum.

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Reticular opacities are, again, a form of

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something that we perceive from radiographs or CTs.

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And from that information, we try then to deduce

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what the pathology is and the potential etiology.

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So as you know, this is the morphology that we've

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been going through, and we'll be focusing on reticular

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opacities specifically in this session on septal lines.

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Now, what are reticular?

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Opacities?

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These are lines and lines that really they don't branch.

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And there are different forms of

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reticulation, which kind of means net-like.

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There's re that's sort of the so-called

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curly lines where they're perpendicular

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one to two centimeters from the pleura.

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So-called curly lines which radiate to the hilum.

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And then there's the other ones, which

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are the thick reticular opacities here,

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which we'll talk about in the next session.

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And then the curved reticular opacities

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that we'll talk about in the third session.

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So Interlobular Septation, what is it?

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This is usually what we refer to when we see

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reticulation with the so-called septal thickening.

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The Interlobular Septations are the sheetlike structures

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that form the girder system of the lung, and they

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contain, uh, veins and connective tissue and lymphatics.

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And this is, uh, from Dr.

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Ito's lab, uh, radiograph of the specimen.

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And you can see a beautiful secondary pulmonary lobe.

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This is the, uh, central lobular airways.

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The arteries and the veins are lying within these.

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Septations along with the lymphatics, and

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you can see how they go right up to the

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subpleural surface and then continue along.

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And then the so-called curly lines, or the interrelated

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sort of septal thickening tend to meander the.

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Towards the hilum.

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Again, they don't tend to branch, so when you

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see these thickened, they'll look like lines

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that are sort of extending out from the hilum.

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So these are the septal lines.

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Differential is very small.

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The hardest thing is seeing 'em, right?

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It's all about that perception, picking them up.

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But almost always when you start seeing the septal

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thickening, it's gonna be hydrostatic pulmonary

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edema, so-called congestive heart failure.

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But there are a couple of other things.

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One important one is lymphangitic spread of tumor,

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which is almost always gonna be adenocarcinoma.

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Pick the most common for the

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patient's age and sex or lymphoma.

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Some rare ones, early AVMs can give it 'cause it

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looks like hydrostatic edema and acute eosinophilic

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pneumonia, which Eric Milne used to call allergic edema.

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So extensive septal thickening.

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In this patient, you can see nicely these

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so-called Curly A. Don't bother calling 'em Curly.

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Curly was a name.

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Just say septal thickening.

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They're all the same.

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And then the septal thickening along here. Now—

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just as a note, we're often taught to

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look in the costophrenic angles, and—

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you might see the septal thickening

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there, but there's not a lot of lung there.

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But if you look in the lateral projection,

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in that retrosternal space—my God,

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you'll see all sorts of them there.

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If they're there, you'll see these little

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perpendicular—like a stepladder going up—and you

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can also see the ones that undulate back to the hilum.

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The other place I tend to look,

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oddly enough, is the apices.

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I tend to see them there also.

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Okay, so again, just kind of a representation.

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These are septal thickenings.

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There's associated lower lobe consolidation.

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This is characteristic of congestive

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heart failure or hydrostatic edema.

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Okay?

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On CT, this is what they look like, right?

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They often reflect these lymphatic thickenings.

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From whatever fluid or such.

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Remember, lymphatics kind of are a sump pump,

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and you can see there. And also, you'll tend to

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see subpleural, fissural thickening, maybe some

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effusion, and it's just thickening of these.

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Interlobular septations.

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Now, just quickly about lymphatics—

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the function is like a sump pump.

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It takes away particles and

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fluid, and it's usually very slow.

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The production and flow relate to the driving force

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of the pulmonary artery pressures, and since the

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pulmonary artery pressures are so low posteriorly

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in the upper lobes and the superior segment, we

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tend not to see very much of the septal thickening.

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The other thing is that the

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chest wall motion is theorized—

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theorized to also improve lymphatic flow—so we

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don't see much septal thickening in the upper

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lobes and posteriorly in the superior segment.

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This has a direct effect on

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manifestations of some chronic diseases like—

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cavitary tuberculosis, which you almost

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never see anteriorly but posteriorly.

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It's not because of high oxygen,

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which is commonly taught.

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A nice example—this is congestive heart failure.

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Remember, the septal thickening reflects the lymphatic

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drainage, and you can see in the lower lobes there's an

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awful lot of these septal lines, along with effusions.

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But as you go up, you notice that they're

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more anterior and not very many posterior.

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And this is also why, in the lateral

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projection, that retrosternal area is a good

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place to look for those septal thickening.

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And you can see 'em in the apices,

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anteriorly more than posteriorly.

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Okay, now here we've got two patients, and I'm

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showing you the lateral, and they both have septal

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thickening, but they're a little different.

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This one—um, if you don't notice it, it's okay—

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but over time, you'll start noticing, you know,

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there almost looks like there's some nodularity

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to this one.

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I don't see that here, but I see the nodularity there.

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When you see those little nodules in there, or

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when you think you see them, that should raise

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a red flag that you're probably dealing with

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something besides congestive heart failure. And the

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big one to consider is lymphangitic spread of tumor.

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You could consider sarcoid, but I'll get into

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that later in a perilymphatic nodularity talk.

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But sarcoid doesn't tend to give you as

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much septal thickening. But this is very

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characteristic for lymphangitic spread of tumor.

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You have your septal lines, and you have your

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perilymphatic nodularity that follows the

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lymphatics, kind of in a beaded appearance. How

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can you tell? Well, it's usually asymmetric,

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and it won't respond to diuretic therapy.

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Okay.

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Another patient.

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You have septal lines.

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You can see the septal lines there, but

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in addition, you almost wonder if there's

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a little nodularity along the fissure.

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If you don't see it, don't worry about it,

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but you should take a look at this and go,

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holy macro, that's all on the right side.

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That's not gonna be congestive heart failure.

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Probably not hantavirus. Probably not

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acute eosinophilic pneumonia.

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Oh, snap.

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I think this is lymphangitic spread of tumor.

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Another patient with septal thickening, and

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there's the lung cancer right there.

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There's this kind of beaded, undulating

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thickness and thinness—nodularity, unilateral.

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So the asymmetry and the perilymphatic nodularity

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should clue you in that this is going to most likely

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be the spread of tumor. Again, most likely adenocarcinoma

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or lymphoma—in this case, adenocarcinoma of the lung.

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So this is, uh, from Dr.

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Ito's lab again, and you can see how there are

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some areas that do look like smooth septal thickening.

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'Cause you can have smooth, but it, it,

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there'll be some areas of nodularity as well.

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37-year-old, increasing dyspnea over three weeks.

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Septal thickening.

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But it, it, it's asymmetric, right?

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It's here, and there's a little bit

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here, and that's kind of funny.

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And 37-year-olds with congestive heart failure?

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Well, you know, I'm also noticing that

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the, the mediastinum is too dense.

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The aortic pulmonary recess is convex.

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Oh, that suggests that

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there's, uh, adenopathy here.

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And you'll also note she's missing her left breast.

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So in this case, this is most characteristic for

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lymphangitic spread of tumor from metastatic breast cancer.

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Could it be sarcoid?

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Maybe, but probably not.

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You can see the hilar adenopathy really

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well on the lateral, the so-called donut

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sign, which I've talked about before.

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And again, when you look at the septum,

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you, you know, you can see it, and it's like,

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well, if it looks smooth, it looks smooth.

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But if you suspect, like here, there's

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some nodularity, it's okay to say, "Hey,

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you know, there may be some associated

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lymphatic nodularity."

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Now get a CT.

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Think, consider lymphangitic spread of tumor.

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All right.

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Another patient, 18-year-old,

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increasing dyspnea for one day.

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Well, she's got some septal thickening.

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She's got bilateral lower lobe ground-glass.

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You can see the septal thickening

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best in the lateral subpleural.

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Pleural thickening.

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All right.

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No effusions really that I'm seeing, but it's kind of

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funny for her to have congestive heart failure, right?

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Hydrostatic edema.

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They got a CT, and it's just

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widespread septal thickening.

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She did not respond to diuretics.

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That's a clue.

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Hydrostatic edema should respond

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to diuretics very quickly.

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She did not.

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Red flag.

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This is going to be something else.

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In this case,

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this was acute eosinophilic pneumonia,

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and she responded promptly to steroids.

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Remember, Melanie used to call this allergic edema?

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That was a pretty good title.

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That's a pretty good name for it, actually.

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And then another patient. You may not ever see this,

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but a patient with fever, you have septal thickening.

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It's a little asymmetric, some effusions.

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This turned out to be Avium.

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They soon went into ARDS.

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Diffuse alveolar damage over the next, uh, couple of days.

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So that's the summary of septal thickening.

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The hardest thing about it is perceiving it.

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So try looking in the lateral retrosternal region.

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If you have a lateral, that's

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usually the best place to pick it up.

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There's more lung, and again, lymphatics tend

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to occur mostly in the anterior lung, not

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the posterior, except in the lower lobes.

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It's a short differential.

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It's usually hydrostatic pulmonary

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edema, congestive heart failure.

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But if they don't respond to diuretics or if it's

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asymmetric or you think there's some perilymphatic

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nodularity, you gotta be suspect for another etiology.

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Okay.

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Thank you so much for listening.