0:00

So now we are on an MRI image.

0:03

This is a fluid-sensitive

0:06

fat-suppressed sequence.

0:08

Now, whether it's a T2 fat sat or STIR, that

0:10

doesn't make a big difference, but I think

0:12

if you just describe it as a fluid-sensitive

0:14

fat-suppressed sequence, you sort of avoid

0:17

the issue of having to call it STIR or T2.

0:19

So if you're, for the trainees out there,

0:20

if you look, somebody's asking you a

0:21

question, and you don't know what it is,

0:23

just say that.

0:24

A fluid-sensitive fat-suppressed sequence.

0:26

So we're going to take this image

0:27

now, and I am going to show you

0:30

what the different layers look like.

0:31

So we noticed before on the video,

0:34

we talked about the five-seal component.

0:36

So what is the five-seal component?

0:38

It is,

0:42

we're going to concentrate on this area

0:43

right here, particularly this one right here.

0:47

Okay?

0:48

So if you notice, there is a tri-laminar

0:51

appearance, three layers, tri-laminar.

0:54

You've got bright, you've got

0:57

dark, and you have bright.

1:00

Okay, and we know this is the epiphyseal side.

1:04

We know this is the metaphyseal side.

1:07

Similarly, over here in the proximal tibia also.

1:11

But I'm going to concentrate on the

1:13

femur just because it's easier to

1:14

draw, and that's a bigger structure.

1:17

We said that on the epiphyseal

1:18

side, this bright structure is what?

1:22

That is where you have your

1:24

big cartilaginous cells, right?

1:27

They're hypertrophied.

1:28

The cells have a lot of water.

1:30

That's unbound, that's why it looks bright,

1:33

because it has a lot of water content.

1:36

The dark area, this, why is that dark?

1:39

That's the zone of provisional calcification.

1:41

Matrix is being laid down, calcification

1:44

is happening, and calcification, an MRI, no

1:47

matter what sequence you're looking at, it's

1:50

going to be dark, like you see over here.

1:53

Finally, you've got this bright

1:55

structure here on the metaphyseal side.

1:57

That's where all the blood vessels

1:59

are coming in, and they're releasing.

2:02

The humeral factors into this area, so

2:05

that's because the humeral factors, the

2:06

blood vessels in that area have to be leaky.

2:09

The capillaries, and they have lots

2:10

of fluid, again, because you have

2:12

so much fluid that's unbound to

2:13

macromolecules, that appears bright.

2:16

So whenever you look at the physis

2:18

in a pediatric patient, always look

2:21

for that trilaminar appearance.

2:22

If you don't see that trilaminar appearance,

2:25

where there's a disruption, then that means

2:27

that there's something wrong with the physis.

2:30

Um, maybe there is an old infection, maybe

2:32

there is prior trauma, but something has

2:34

disrupted that zone that's not normal.

2:37

If you look very carefully, I'm going

2:39

to erase a couple of these things,

2:43

you can see something similar

2:44

but maybe not to the same extent

2:49

in the secondary ossification center over here.

2:51

Look at the periphery.

2:52

You can see some of the brightness.

2:55

You can see the darkness; it's a little

2:56

harder to appreciate, but something similar

2:59

is actually happening in the epiphysis.

3:02

Because you also have an area of cartilage

3:05

that's now getting ossified, but this

3:07

is happening in a spherical fashion.

3:10

Instead of happening in the longitudinal

3:12

fashion that you see in the metaphysis,

3:15

you have it here in a spherical fashion,

3:18

going from inside to outside,

3:21

where cartilage in the center is

3:23

becoming bone and expanding peripherally.

3:27

So both these processes are known

3:29

as endochondral ossification.

3:31

Endochondral means that inside the cartilage,

3:33

inside the cartilage, it's being ossified.