0:01

So let's talk about approach.

0:02

We all wanna get to the diagnosis, right?

0:04

And in a lot of, uh, musculoskeletal radiology,

0:07

we're accustomed to looking for the primary finding.

0:10

We're faced with a clinical question like, uh,

0:12

ligament tear, right?

0:13

And so we go right to the anatomic region

0:16

and evaluate the ligament itself and try

0:18

and determine if it's in continuity or not.

0:21

The problem with doing that in nerve imaging is

0:23

that the nerves are very small,

0:25

and in some cases, even when there are a very convincing

0:29

clinical picture and EMG findings, uh,

0:31

to suggest a nerve abnormality, it will look for all intents

0:34

and purposes completely normal on MRI.

0:37

And so this is actually a pretty tough place

0:39

to start when you're identifying these cases.

0:42

And one thing to keep in mind is

0:43

where we're really gonna help the surgeons is in

0:46

identifying an underlying cause.

0:47

So we'll come back to that. So probably a better place

0:50

to start when you, when you look through the MRI

0:53

of these cases is for those secondary imaging findings.

0:57

And what the secondary findings are predominated

0:59

by are muscle abnormality.

1:01

So remember, the muscles are really kind

1:02

of the end unit of those nerves.

1:04

Uh, when the nerve is injured,

1:06

those muscles undergo changes in a

1:07

pretty characteristic way.

1:09

Uh, so we're looking for those

1:10

signal changes within the muscle.

1:12

Bare bellies, much bigger realistic, right?

1:14

Easier to see on those axial sequences.

1:17

And then secondarily, we need to understand those patterns

1:20

of involvement so the individual nerves have

1:23

different distributions.

1:24

And so understanding the distribution

1:26

of muscle involvement really helps guide your search.

1:29

So once you've screened these cases,

1:31

you identify the muscle abnormality

1:32

and you say, Hey, this looks like a radial nerve

1:35

distribution, then you can go back

1:37

and look at that radial nerve itself, try

1:39

and find the underlying cause or potential abnormality.

1:43

But I'll tell you one secret to these cases,

1:45

and that's most of the information

1:47

that you need is right here in the clinical picture.

1:50

So these cases in particular,

1:52

I'm really delving into the chart.

1:54

I wanna know all of the clinical manifestations,

1:57

the chronicity of, um, of symptoms in these patients.

2:00

The physical exam findings, a lot

2:02

of time you get supporting information

2:04

before you get imaging.

2:05

So you'll have EMG findings as well.

2:07

Uh, and by the time the patients come for MRI imaging, uh,

2:12

they've been evaluated typically by a subspecialist, uh,

2:15

whether that's a specific to nerves or to surgery.

2:18

Um, they will have a general idea of

2:20

what the abnormality might be.

2:22

So MRI is really helpful in confirmation

2:25

and again, identifying those underlying causes

2:27

of potential entrapment.

2:29

We're really trying to help guide

2:30

the surgeon in these instances.

2:32

Is this something that can be intervened upon?

2:34

Where is the abnormality so they know where to search, uh,

2:37

where, where to start their kind of surgical approach.

2:39

So start with that clinical information.

2:41

Really gather as many clues as you can.

2:44

And then when you start looking at the cases,

2:46

look at the muscles first.

2:48

I really like those axial sequences.

2:50

You can kind of quickly scroll through a stack

2:52

and see if you can see any of that denervation change.

2:55

Um, if you do try

2:56

and identify, is that a pattern? Is it a single

2:58

Nerve distribution or is it multiple?

3:01

And then if you identify a single nerve,

3:02

then you can go back and look

3:04

for those primary abnormalities of the nerve

3:06

and then try to identify

3:07

that underlying cause we can wrap it up nicely in a package

3:10

and, and send it back out, uh, to the medical record.

3:14

So, uh, as similar to our approach, let's talk about some

3:18

of these secondary findings.

3:19

So again, we're looking at the muscles

3:21

and we're looking for that denervation change

3:23

and it progresses from our acute findings, which can occur

3:27

as early as 24 hours after nerve abnormalities.

3:30

So nerve injury, um, is usually the best example in

3:33

how they determined that.

3:34

You could see muscle signal changes that early on.

3:38

Uh, then they kind of progress into this subacute phase,

3:40

which has a variable length of time, depending on

3:43

what you read before we really get into the chronic changes.

3:46

So early on in that acute phase, it's what you might expect.

3:49

We see edema, we haven't lost any

3:51

of the muscle volume at this early phase.

3:53

In fact, sometimes the muscles are a little bit enlarged,

3:56

but we're looking for that increased signal on

3:58

fluid sensitive sequences.

4:00

And in the chronic phase, we're looking for

4:01

that fatty replacement, that infiltration of the muscle

4:04

and overall volume loss.

4:06

Once you get to true chronic, uh, fatty infiltration

4:09

of the muscles, you really lose any T

4:11

two signal abnormality.

4:13

So don't be surprised to see a complete absence of, uh,

4:16

T two signal abnormality

4:17

and, uh, a large presence of fatty atrophy and infiltration.

4:23

And primarily when we're identifying, uh, the course

4:26

of those nerves, we wanna check to make sure

4:28

that there isn't any abnormal angulation.

4:31

We're looking for mass effect, kind

4:33

of moving the nerves away from their normal course.

4:35

Uh, any abrupt changes as well in kind of the,

4:38

the typical anatomic, um, course of the nerve is gonna be

4:41

concerning for abnormality.

4:43

And then next we wanna check the nerve caliber.

4:45

So this is where those axial sequences are really helpful.

4:48

You can kind of compare, you know, one axial slice

4:51

to another is the nerve all of a sudden getting larger.

4:54

Uh, you can also have decreased size

4:56

of the nerve in some instances

4:58

that is more chronic injury to the nerve.

5:00

And finally, signal abnormality.

5:02

As we can see in this image

5:03

of the elbow here in the bottom right, we have some areas

5:06

where, uh, there's increased signal in the nerve.

5:10

It's pretty hyper intense in this instance.

5:12

And you can see these individual

5:14

fales identified by the blue arrow.

5:16

Those are enlarged. They kind

5:17

of have variable size in this instance.

5:20

And one trick that's great, uh, about nerve imaging

5:23

and what I would recommend you to do on any case

5:25

where you have, uh, images of the nerve,

5:27

which is pretty much every joint that you'll image in M msk,

5:30

is look for the normal nerves

5:32

and identify what their typical signal is.

5:35

So we have great comparison in this instance.

5:37

This is the median nerve compared

5:39

to our abnormal ulnar nerve.

5:41

You can see that the nerve itself is relatively iso intense,

5:44

maybe a little bit hyper intense to the muscle,

5:47

but certainly not approaching that fluid intensity signal

5:49

that we see here in the ulnar nerve.

5:51

Um, because there are often multiple nerves in

5:54

the same axial slice.

5:55

You have this great kind of internal comparison.

5:58

Internal control of normal, uh,

6:00

can be really helpful when you're evaluating these cases.