0:00

On the previous vignette, I showed you this

0:03

six-year-old patient's radiograph, which

0:06

demonstrated some collapse and sclerosis

0:09

of the right femoral head, a little bit

0:11

of lucency under the subchondral surface,

0:13

and what looked like a joint effusion.

0:17

This is the MR, and I think we can

0:19

see many of those findings here.

0:21

We have a coronal, fat-suppressed,

0:24

fluid-sensitive sequence.

0:26

All this bright stuff in the joint is

0:28

fluid, and look how asymmetric it is

0:30

compared to the contralateral normal side.

0:33

So indeed, there was joint effusion, as

0:36

manifested by displacement of some of the soft

0:39

tissue structures on the plain radiograph.

0:41

That area of subchondral lucency is seen very

0:46

well as an area of high signal, serpiginous, just

0:49

under the chondral surface on the right side.

0:52

And the fact that the head is a little

0:54

flattened up here, compared to the

0:57

contralateral side, tells me that there is

0:59

a little bit of collapse that has happened.

1:01

So these are all signs of decreased perfusion,

1:05

or not getting enough blood supply, avascular

1:07

necrosis, however you want to call it.

1:09

In addition, what this shows that the plain

1:12

film doesn't show is that some of these

1:15

changes are also happening in the metaphysis.

1:18

Look how the metaphysis is brighter.

1:20

On the lateral side and also on the

1:22

medial side, showing that there is some

1:24

added stress happening causing edema,

1:27

and inflammation in this area, okay?

1:30

And there's also some areas or some

1:32

pockets of increased fluid-like signal

1:35

in the capital femoral epiphysis.

1:38

I want to show you the value of

1:41

contrast imaging on a patient like this.

1:44

So I'm going to bring up three images at once.

1:47

So on this one, I'm going to put the

1:49

coronal T1 Fatsat, which is this.

1:56

In the middle image, I'm going to

1:58

put coronal T1 Fatsat post-contrast.

2:04

And on the final, I'm going to put a

2:05

coronal T1 Fatsat subtracted image.

2:09

In fact, I'm going to go just like this,

2:11

so you can see as much of this as possible.

2:14

And really, you want to look

2:15

at both sides at the same time.

2:18

Again, this is fat-saturated without

2:22

contrast, and this is fat-saturated

2:24

T1 with IV contrast in place.

2:28

And this here is a fat-saturated subtracted image.

2:32

In other words, I took this image

2:34

and digitally subtracted out this

2:37

image to give you this image.

2:40

So, pre-contrast, we sort of

2:42

see the areas of effusion.

2:43

We see a little bit of collapse.

2:45

You know, we see the area of abnormal

2:47

signal here that was shown as bright

2:49

signal on the STIR on the lateral aspect.

2:51

After we give contrast, we notice that there

2:53

is considerable enhancement of the synovium.

2:56

There is enhancement in the area of edema.

2:59

There is enhancement in the area in the

3:00

periphery here, both laterally and medially, but

3:04

no significant enhancement in the femoral head.

3:08

Compare it to the normal left side.

3:10

There should still be some minimal

3:13

enhancement on a normal ossified femoral

3:17

capital epiphysis, as we see over here.

3:19

The reason we get the subtracted image is if

3:22

there are subtle findings of decreased enhancement

3:24

on one versus the other, it becomes magnified.

3:27

It becomes really much more

3:29

conspicuous than the subtracted images.

3:32

Look at this image and this image.

3:34

Yes, you can tell there's a difference

3:35

between this and this, but look how dramatic

3:38

that difference is in the subtracted images.

3:41

So if you do post-contrast images looking

3:44

for avascular necrosis, it really behooves

3:47

you to get subtracted images, because if

3:49

there are subtle changes, maybe not as

3:51

dramatic as this, you will pick it up on

3:54

the subtracted images, where you may not

3:56

pick it up on the non-subtracted images.

3:58

Again, we see beautifully the areas of

4:00

contrast enhancement, in the synovium, in

4:03

the metaphysis, and at the periphery of the

4:06

epiphysis, with a central area of non-enhancement.