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Dr. P back with our 72-year-old woman with a

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3 00:00:03,390 --> 00:00:05,790 greater than four centimeter mass known now to

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us as an angiomyolipoma. Angiomyolipomas can be

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classified as classic with macroscopic fat and

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what we call lipid-poor AMLs depending upon

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their appearance. I put up before you an axial T2

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non-fat suppressed and one that's pretty, pretty

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heavily fat suppressed. Now on the standard T2

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Uh, the lesion is somewhat hyperintense, but not

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that much greater in signal than the surrounding

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fat, but certainly hyperintense to the kidney.

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On the fat-suppressed image, a large

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component of the lesion is dark and fat

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suppressing, but some components are white.

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So you're probably asking, well, what's

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the signal intensity on T2 imaging?

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And the answer is, it depends.

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Depends on the vascularity, how much smooth muscle.

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Do you have pseudoaneurysm formation, and how much fat?

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So, you can't really use the T2-weighted

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image as what I call the DECIDA scan.

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You've got to go through everything, especially

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looking at something that is very sensitive for

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fat, like fat suppression imaging, or Dixon method

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imaging, or in-phase or out-of-phase, uh, imaging.

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These lesions, as we said

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previously, are hypervascular.

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Now, classic AMLs are easier to diagnose than these.

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Because they have the typical pathologic

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hallmark of macroscopic fat, seen

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on even a basic T1-weighted image.

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And they're readily identified

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on cross-sectional imaging.

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But the lipid-poor ones, you know, that may be a

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challenge to differentiate from renal cell carcinoma.

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This is a pretty exophytic,

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uh, looking lesion right here.

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And that's a critical diagnosis.

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In my experience, most renal cell carcinomas

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don't have this very exophytic irregular appearance.

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They may be exophytic, but they tend to

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have more of a smoother, rounder appearance.

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But in ambiguous cases, you're going to have

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to use a number of factors, diffusion imaging,

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the parametric factors when you inject the case

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to see how much vascularity there is in there.

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Both can be very vascular, and how much

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washout you may experience thereafter, and

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sometimes it can be extremely difficult.

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I have seen kidneys completely resected

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from Wunderlich Syndrome with a massive,

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massive hemorrhage from an AML, and it's not

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until you get the specimen on the table that

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you realize you just took out a benign lesion.

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Now, the presence of macroscopic fat can be

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appreciated as suppression of signal intensity

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on these fat suppression images, as you've seen.

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Especially on the India ink

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artifact scan, the out-of-phase.

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So if you can't do Dixon method, just

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do in-phase imaging and out-of-phase

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imaging, as you've seen previously.

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Now, benign lesions, as we've said before,

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including classic AMLs, may be exophytic.

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But this angular interface, and you do have

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a little bit of a claw sign here, admittedly.

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But this sort of angular, irregular appearance

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supports the diagnosis of angiomyolipoma,

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and I'm scrolling through it on the

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T2 and the T2 fat suppression imaging.

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But in some studies, such as the study by

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Takayashi, Takayashi and others, the angular

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interface sign is present really uncommonly,

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less than 10 to 20 percent of the time.

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So that alone isn't going to get you off the hook.

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You'll also hear the sign, the mushroom sign, where

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the lesion appears to mushroom right out of the kidney,

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which it's doing right here on the T2-weighted imaging.

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So there are a number of things you can use.

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The mushroom sign is one of them.

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Hypervascularity.

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Relative lack of washout.

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The absence of diffusion restriction.

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The presence of macroscopic fat.

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Perhaps the angular interface sign, the demographics,

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usually an adult or slightly older woman.

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All of these things combined might help you

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towards the diagnosis of the benign angiomyolipoma

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and away from renal cell carcinoma, which

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can also have micro and macroscopic fat.

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Dr. P out.