0:00

So again, I'll give you a moment to kind of look through these images.

0:04

Little bit of clinical history in this case, this was a 44 year old man.

0:09

Uh, he had a workplace injury. He presented with some dust, uh,

0:13

deltoid muscle wasting,

0:14

and he had a single nerve that had conduction block on E M G.

0:18

I won't give it away for you here,

0:19

but give you a chance to kinda look at these images. So,

0:22

same setup for most of these cases.

0:24

We're gonna have a T1 sequence here on the left. Uh,

0:26

we'll have some sort of fluid sensitive,

0:28

typically a T2 fat sat or a PD fat sat on the

0:33

screen, right? And going from lateral to medial.

0:41

Let me give you one more imaging plane here, or two more imaging planes.

0:45

So our axial, we're starting from distal moving proximal,

0:49

or more cranial in the shoulder

0:54

and on our coronal sequence.

1:00

And one more time from posterior to anterior.

1:06

Right. And we're ready for our next pulling question, question number two.

1:13

So isolated edema,

1:14

atrophy of the tes minor is most commonly associated with what type of

1:19

injury? What type of injury is this? Posterior subluxation,

1:23

anterior subluxation cuff tear or humeral head fracture. Uh,

1:28

the correct answer is, uh, the posterior subluxation and dislocation.

1:33

So a little bit of a red herring.

1:34

You certainly can get other nerve injuries with other dislocation events, uh,

1:38

but the TE's minor muscle is often kind of the culprit, um,

1:42

or the recipient of injury in these cases. Uh,

1:46

so let's talk a little bit more about axillary nerve injury in this

1:51

case was not, uh, associated with a subluxation or a dislocation event.

1:55

Um, but rather a kind of a stretch injury.

1:58

And we'll look at that case in more detail,

2:00

but just a few notes about axillary nerve injury or entrapment. Um,

2:04

the axillary nerve is very similar to the suprascapular nerve in that the

2:08

impingement kind of presents with similar imaging features only in axillary

2:13

nerve cases. Instead of supra and infra muscle involvement,

2:16

we're really looking for that tes minor muscle involvement with or without the

2:20

deltoid muscle abnormality.

2:21

Now the deltoid muscle abnormality may be more apparent clinically, uh,

2:26

because the tes is rather small and there's other muscles that help support the

2:30

function. So a paralabral cyst remains the most common cause. Um,

2:34

but in some cases, such as with subluxation or dislocation,

2:38

you can have a nerve injury.

2:41

So let's go back to that and look at a few of those imaging findings here.

2:47

So just starting with our fluid sensitive sequence,

2:50

hopefully that muscle pattern abnormality really jumped out to you.

2:53

In this case, you can see that there's quite a bit of atrophy here.

2:56

We've lost the volume. You have kind of this con

2:58

Conc concave appearance of the muscle border of the, uh, deltoid.

3:03

And as we get kind of more, uh, lateral on the shoulder,

3:06

you can really appreciate that deltoid muscle edema. Uh,

3:10

so we know by the pattern of denervation we're looking for axillary nerve

3:14

abnormality.

3:15

So I like to follow the axillary nerve kind of from its distal region more

3:19

proximal cuz I think that's where it's easiest to see. Uh,

3:22

we can see it here kind of in this axillary recess. Um,

3:25

we can see the distal branches. They may be a little bit hyperintense.

3:29

And as we go more medial,

3:31

we're gonna see the more proximal course of this nerve.

3:34

So we can see the nerve adjacent to this region here. Uh,

3:37

we're just anterior to that axillary recess. Coursing more proximal coursing,

3:42

more proximal. Were just, uh, anterior to the subscapularis muscle.

3:46

And this is where the nervous starts to be abnormal in this case. In fact,

3:49

we go from pretty uniform, uh, signal intensity.

3:53

It might even be a little bit bright in this case it should be iso or slightly

3:57

hyperintense to muscle, but this is pretty bright.

4:00

We can see that it's really heterogeneous enlarged here. Um,

4:04

there's even some kind of cystic change and there's kind of a gap.

4:08

We go from seeing some portion of the axillary nerve here and then we see that

4:12

it's kind of discontinuous with the rest of the nerve.

4:15

And this is concerning for a, a partial transection, uh,

4:19

secondary to a stretch injury.

4:20

So let's see if we can see that on our other sequences here on the axle. On the,

4:25

um, sorry, the, uh, ax sequence here. You can see the course of the nerve,

4:30

uh, lots of increased signal along its course.

4:33

You can see it coming off of the plexus, um,

4:36

hyperintense enlarged and heterogeneous.

4:40

And with the corresponding kernel,

4:42

we really get just kind of the very proximal aspect of the nerve abnormality

4:45

here. But you can compare it to the adjacent, uh,

4:48

nerve branches and see that it's abnormal.

4:51

Now there's a little bit of a red herring in this case.

4:53

There is a paralegal cyst, right? Uh,

4:55

so that could have contributed somewhat to some of this denervation,

4:58

but we can see that that cyst stops a little bit short of the course of the

5:02

nerve and the more proximal nerve abnormality is much more pronounced. And so,

5:06

um, it was thought to be that this was more of a partial nerve transection as

5:11

opposed to paralabral cyst and nerve impingement.