0:00

Okay, we're coming to the final case of our

0:02

cartilage series; it's another bony tumor.

0:06

Here we have a lateral and

0:07

frontal projection of the ankle.

0:09

Notice, again, the physes are widely

0:11

patent and we have a lytic lesion that has

0:17

sort of well-defined margins and kind of bubbly

0:20

in appearance, as somebody would say.

0:22

Let me outline the lesion for you both on

0:24

the lateral and the frontal projection.

0:27

On the frontal, I think it's a little easier.

0:28

It's going to be something like this.

0:31

And if you notice, there are areas

0:32

that are sclerotic, the margins, and

0:34

areas that are not so sclerotic.

0:36

That's also important to describe.

0:39

And on the lateral, it's a little bit more difficult.

0:41

I actually think it starts way out here.

0:45

It comes in like this.

0:48

Probably goes somewhere over here.

0:49

Here I lose it a little, but this is an

0:51

approximation of what that looks like.

0:54

Again, it abuts the articular surface.

0:56

It's eccentric.

0:58

There are no pathological fractures.

1:00

And, you may be tempted to say there's no

1:03

periosteal reaction, which is a true statement,

1:06

but remember tarsal bones form with endochondral

1:09

ossification, meaning that they form bone

1:12

within cartilage and there is no periosteum.

1:15

So if you have injuries or tumors in

1:18

tarsal bones like this, you're not going to

1:20

see periosteal reaction because there is no

1:22

periosteum. Something to keep that in mind

1:25

so you don't want to say, "Oh, there's no

1:26

periosteal reaction." You're just not going to

1:28

look very smart by saying that in a tarsal

1:30

bone. Another thing to keep in mind is tarsal

1:34

bones are what we call epiphyseal equivalents.

1:37

What does that mean?

1:39

Epiphyseal equivalent means that

1:41

lesions that occur in the epiphysis also

1:43

tend to occur in these tarsal bones.

1:46

So when I see a tarsal bone lesion,

1:48

I think, "Oh, is this something that I

1:49

typically would see in an epiphysis?"

1:51

And in this condition, yes.

1:54

I'm going to bring the CT here,

1:56

again, for consistency, the sagittal

1:59

there, and a coronal over here.

2:02

We again see a beautiful,

2:04

well-marginated lesion within the

2:07

oli; again, very well-marginated.

2:09

The CT does a great job of showing the

2:11

margins, no pathologic fractures abutting the

2:14

articular surface here, eccentric in location.

2:19

Feas are still patent.

2:22

Okay.

2:23

What the CT and plain film don't

2:27

tell us is what does the internal

2:29

architecture of this lesion look like?

2:32

You know, is there bony edema?

2:34

You cannot find that out with CT and plain films.

2:36

For that, of course, we need MRI, and you have

2:39

all these studies available to you up here.

2:43

So let's bring the sagittal.

2:44

This is a fat-suppressed,

2:46

fluid-sensitive sequence.

2:47

I'm bringing a coronal SE.

2:49

This is our cartilage-specific sequence.

2:52

So here is a lesion.

2:54

What do we notice right away?

2:55

There are multiple bubbly areas.

2:57

They're somewhat septated, right?

2:59

I don't really see any air-fluid levels, per se.

3:02

Maybe one over here, actually.

3:04

So, yes, aneurysmal bone cyst

3:07

is the differential, but this is

3:09

an epiphyseal equivalent lesion.

3:11

So if you saw this in the epiphysis,

3:14

eccentric, abutting the articular

3:15

surface, what would you call it?

3:19

I would call it a chondroblastoma.

3:21

And what do you notice here?

3:22

Lots of edema, right?

3:24

No self-respecting chondroblastoma

3:28

would have no edema.

3:30

If there's edema, it's chondroblastoma.

3:32

Epiphyseal equivalent lesion.

3:34

There's edema, in fact, that extends

3:36

out into the soft tissues also.

3:38

That's the sagittal view.

3:40

Now where the fat-suppressed sequence really

3:41

helps us out is look at the signal

3:43

characteristic of the central portion.

3:45

That's sort of the fluid-like portion.

3:47

But look at the periphery.

3:48

It has a somewhat grayish appearance.

3:51

And what does that resemble?

3:53

It resembles the cartilage of your chondral

3:57

surface, articular surface, and your physis.

4:00

So we know this is probably cartilage tissue.

4:03

So this is a slam dunk chondroblastoma

4:05

because it has cartilage-like tissue, it's

4:08

eccentrically located, it's in an epiphyseal

4:10

equivalent bone, and there is marrow edema.

4:14

Great example of chondroblastoma

4:16

in a tarsal bone.