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So here's an example of a patient that presents

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with a right-sided neck mass that really allows

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us to emphasize our approach to evaluate the

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brachial plexus and also to review the anatomy.

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Remember, the three primary components

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to identify the brachial plexus are to

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look for the anterior scalene, the middle

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scalene, and the subclavian artery.

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And sometimes we do use the term

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middle and posterior together.

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So, on the left-hand side, we

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see this mass right here that's

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involving the right side of the neck.

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Now, one of the biggest challenges

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that you could have is, well, you

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know, is this a lymph node or not?

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Well, the first thing that you have to do in

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something like this is to look at all the images

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and identify the normal anatomic structures.

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So, where the arrow is pointing at right

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now is the anterior scalene muscle, and if

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we look posteriorly, here's that posterior

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scalene muscle, and right between those

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two planes of the muscle right here,

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is the plane of the brachial plexus.

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Now, if we draw a line down the middle and

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compare the left side to the right side, what

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we see here is this little strip of muscle

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that's displaced anteriorly, and we can see

1:07

another muscle that's displaced posteriorly.

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So this anterior muscle is the anterior

1:12

scalenE muscle, and this posterior muscle is

1:14

the posterior scalene muscle, which tells us

1:17

that this mass has to be located between the

1:19

plane of the anterior and middle scalene,

1:22

which places it in the brachial plexus.

1:25

Now that completely changes

1:26

your differential diagnosis.

1:28

We've seen earlier.

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In other mastery course examples of

1:31

what a metastatic lymph node is, would

1:33

look like, that would be outside of the

1:36

anterior and the posterior scalene complex.

1:39

Rather, this is within the planes of the

1:41

brachial plexus displaced in those muscles.

1:45

On the non-contrast T1 weighted image, we

1:47

can see maybe it's slightly hyperintense.

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Again, I want to emphasize the fact that there's

1:52

our anterior scalene and our posterior scalene,

1:55

and there's our brachial plexus between it.

1:57

And when we give contrast, we can

1:59

see that the mass is enhancing.

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So when we see that enhancement of

2:03

the mass, it's not necessarily fully

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homogeneous, but there are some small

2:06

areas of non-enhancement that may

2:08

represent a little bit of cystic necrosis.

2:12

Now, when we look at the contrast

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enhanced T1-weighted image, then we

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scroll through it, we can see now that

2:17

there is a component of the mass that is

2:20

extending into the right neural foramina.

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So if you will, this is starting to

2:24

look like a dumbbell-shaped lesion.

2:27

And when we look at the coronal T2-weighted

2:29

images, we can see that this mass is extending

2:32

superiorly and medially, and extending

2:35

into the neural foramen, and extending

2:37

right up to the level of the spinal canal.

2:42

So, what this is, is a neurofibroma

2:45

involving the brachial plexus.

2:47

And the key points to remember is that

2:49

if you do see that neck mass, especially

2:52

involving the lower portion of the right neck,

2:54

in your own mind's eye, you have to figure

2:56

out, is it a lymph node, or is it possibly

2:59

involving the brachial plexus.

3:02

So, in order to make that differentiation,

3:04

again, remember the anterior scalene and

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the middle scalene, and then look and

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analyze it more and see potentially is

3:11

there extension into the neural foramen.

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So in this case, the localization between

3:16

the two planes tells you it's probably

3:18

arising from the brachial plexus.

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And then when you look at the coronal images, we

3:22

can see that component of the lesion extending

3:25

through the neuroforamen, extending into the

3:28

spinal canal, and this is sometimes what we

3:30

would call that dumbbell-shaped lesion, which

3:33

in this case was indicative of a neurofibroma.