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Dr. P here back with our 72-year-old gal,

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3 00:00:04,300 --> 00:00:06,539 who's got an exophytic greater than 4 centimeter

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mass in the inferior pole of the left kidney.

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There it is on the coronal T2-weighted image.

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Here it is on a fat-suppressed,

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uh, image, protruding anteriorly.

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And it demonstrates this phenomenon of angular

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extension outside of the kidney, with somewhat of

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a narrower base, but, uh, has this sort of angular,

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mushroom-like extension we've discussed before.

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But I want to bring a pitfall to your attention.

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Here's some perinephric fat.

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Now, angiomyolipomas are like belly buttons.

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You can have an outie or an innie.

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Most AMLs are outies.

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They go out.

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But what if you had a lesion that went in?

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That is more common for a renal cell carcinoma.

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So what if a renal cell carcinoma decided to do this?

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It decided to grow this way, and

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then engulf the perinephric fat.

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Then it might mimic and simulate an AML.

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So the pattern of growth can be helpful.

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The belly button of a renal cell carcinoma,

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if it's an innie, favors renal cell carcinoma.

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On the other hand, if it's a fat-containing

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lesion, and it's exophytically growing out

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with a mushroom-like appearance, that's

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not pathognomonic, but it favors AML.5 00:00:08,029 --> 00:00:10,200 There it is on the coronal T2-weighted image.

0:10

Here it is on a fat-suppressed,

0:12

uh, image, protruding anteriorly.

0:15

And it demonstrates this phenomenon of angular

0:18

extension outside of the kidney, with somewhat of

0:21

a narrower base, but, uh, has this sort of angular,

0:24

mushroom-like extension we've discussed before.

0:27

But I want to bring a pitfall to your attention.

0:29

Here's some perinephric fat.

0:32

Now, angiomyolipomas are like belly buttons.

0:34

You can have an outie or an innie.

0:36

Most AMLs are outies.

0:39

They go out.

0:41

But what if you had a lesion that went in?

0:43

That is more common for a renal cell carcinoma.

0:47

So what if a renal cell carcinoma decided to do this?

0:50

It decided to grow this way, and

0:53

then engulf the perinephric fat.

0:57

Then it might mimic and simulate an AML.

1:01

So the pattern of growth can be helpful.

1:04

The belly button of a renal cell carcinoma,

1:06

if it's an innie, favors renal cell carcinoma.

1:09

On the other hand, if it's a fat-containing

1:11

lesion, and it's exophytically growing out

1:14

with a mushroom-like appearance, that's

1:16

not pathognomonic, but it favors AML.

1:19

So, remember this pitfall regarding engulfment of the

1:23

perinephric fat, which may simulate an angiomyolipoma.

1:26

A couple of other comments before we quit.

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Lipid-poor AMLs account for 5 percent of

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AMLs, and they're typically reported to be

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smaller, which makes them tougher, with an

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average diameter of 3 centimeters or less.

1:40

A lipid-poor AML is pathologically described as

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an AML containing no more than 25 percent fat

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cells per high-powered field, and lipid-poor

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AMLs are composed nearly entirely of smooth

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muscle and disordered vascular components.

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Now, at MR imaging, these lesions can be pretty

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homogeneous, show low signal on T2-weighted

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imaging, and due to the presence of abundant smooth

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muscle and high signal on the T1-weighted image.

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They can be a little bit confusing, you know,

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is it a small renal cell or is it an AML?

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And this is where in-phase imaging with a lesion is

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slightly bright and then out-of-phase imaging with a

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lesion drops out. At least it helps you identify the fat

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and then you go on to use some of the other components

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and details that we've described. The enhancement

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component of lipid-poor AMLs is typically early intense

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with subsequent washout, but the washout not as great

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as one sees with an aggressive renal cell carcinoma.

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I personally do not, I do not rely heavily on

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the washout characteristics to make my decision.

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I use the character of the growth, and

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maybe sometimes even surveillance, to make

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the decision as to whether I have an AML.

2:51

Lipid-poor AMLs may appear as an

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exophytic but non-round lesion.

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Without a capsule, lipid-poor AMLs may show a

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drop in signal intensity when you go from the

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in-phase to the out-of-phase image, and this is

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a helpful diagnostic criterion to differentiate

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from other non-fat-containing lesions.

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But finally, remember, renal cell

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carcinoma may have micro and sometimes

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macroscopic fat, and so can Wilms tumor.

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With that, it's an AML wrap.

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Dr. P. out.