0:01

Here, we have a 12-month-old boy

0:06

with a mass felt at the very medial aspect of the knee.

0:11

And we could see that mass right over here.

0:13

The image on your left is a coronal T1-weighted image.

0:17

And the image on your right is a coronal T1-weighted fat-saturated image.

0:21

So, I'm going to give you a rule that's almost always true, okay?

0:28

If you have a soft tissue mass in a child

0:31

less than three years of age and it has fat in it, if you could somehow show

0:37

that there's fat in it, it's going to be benign almost all the time, okay?

0:44

The rule doesn't hold anymore if the kid is

0:47

more than three years of age, or if the mass does not contain fat.

0:52

But if you have those two criteria met, less than three years of age,

0:56

has demonstrable fat on MRI, then you can be pretty confident,

1:02

no matter how much it enhances,

1:04

no matter how ugly it may look infiltrating, that it's going to be benign.

1:09

And typically, it's going to be a lesion such as this one, which is a lipoblastoma

1:14

or lipoblastomatosis, or some kind of a fat-containing hamartoma,

1:22

or it could even be involuting hemangioma that has fat in it.

1:27

So all those conditions are benign.

1:30

This one happens to be a lipoblastoma.

1:33

How do I know that?

1:34

It's hard to tell initially,

1:35

but if we look at it closely, these are corresponding slices.

1:40

T1 on your left, T1 fat sat on your right.

1:43

What is fat in this mass?

1:45

The dark stuff isn't fat.

1:46

The fat is going to be, have the same signal as the subcutaneous fat over here.

1:50

So this stuff over here, this bright stuff, that is fat.

1:54

So if that stuff gets dark on the fat-suppressed sequence,

1:58

we can be confident that that is fat we're looking at.

2:01

So looking over here, look at the tissue here.

2:04

That really is darker, isn't it?

2:06

That does...

2:07

look at this part right over here,

2:08

that does get darker relative to this part over here.

2:11

So we know that this mass contains fat.

2:14

And I told you in the beginning that this kid was 12 months of age.

2:18

So now, we can be very confident that this is a lipoblastoma, a benign lesion.

2:23

Now, let's look at the fluid-sensitive sequence, which can look awfully bad.

2:28

Here's a fluid sensitive sequence. Very bright.

2:31

It is well encapsulated,

2:32

but encapsulation in and of itself does not guarantee benignity.

2:37

Okay?

2:37

So don't get fooled with encapsulated lesions.

2:40

Let's look at the post contrast images.

2:42

Looking at the post contrast images, there are areas of enhancement, right?

2:47

Look at this.

2:47

So, looking at post contrast doesn't help you.

2:50

What helps you is the T1-weighted and the T1-weighted fat sat to show

2:55

that there are fat-containing regions that suppress.

2:59

So this is a benign lipoblastoma.

3:02

It may still need to get resected, but it's not malignant.