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Welcome everyone.

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I'm going to talk about a few nerve abnormalities in the upper extremity today.

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Hopefully look at some interesting cases, uh,

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and leave me with a better understanding of what can be sometimes a intimidating

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subject. So, um,

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I'm gonna review some anatomy to start with mostly because I think it really

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helps focus on how, um, I approach these cases. Uh,

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having that kind of search pattern and and um, stepwise approach can really,

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really help narrow differential diagnoses.

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We'll talk briefly about some of the protocol tips that we have and just a

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general approach to these cases. Then we'll look at some unknown cases. Uh,

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each of those, as Ashley mentioned, has a polling question,

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so you can go ahead and participate and follow along. Um,

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and then we'll talk in more detail about each of those different types of cases.

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So go ahead and get started here. So first,

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let's look at the anatomy of some commonly injured or impinged nerves.

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And the first is the suprascapular nerve. Uh,

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if you've taken a standardized radiology test,

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you have certainly seen pathology of this nerve before. Uh,

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just a reminder that it arises from the trunks of the plexus.

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It courses along the under surface of the trapezius muscle,

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along the suprascapular notch and spinal glenoid notch and innervates,

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really the supraspinatus and the infraspinatus muscles. Uh,

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we know that this is frequently impinged, um,

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along the course of that superscapular and spinal glenoid notch. Um,

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we'll see a case example of that here shortly.

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Next is the axillary nerve and the axillary nerve arises from the cords of the

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plexus. It coursees anterior, um,

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along the glenoid and just adjacent to the subscapularis muscle.

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And then it enters the quadrilateral space just distal, um,

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which is just distal to the axillary recess. So, uh,

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just kind of below the glenohumeral joint space there and the axillary nerve

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innervates the deltoid and the tes minor muscles,

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as you can see kind of outlined in orange here in this diagram.

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So moving down to the elbow and the forearm,

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we have the median nerve and on the far left,

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this is at the level just proximal to the nerve bifurcation.

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So we're just distal, uh, to the elbow joint.

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And the median nerve gives off a major deep branch,

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which is the anterior interosseous nerve and it's aptly named cuz it runs just

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anterior or velar to that interosseous membrane depicted in red here.

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And importantly,

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these are the corresponding muscles that are innervated by the median nerve.

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So the median nerve predominantly innervates the muscles of forearm and hand

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flexion. So important to know when you have a little bit of clinical history,

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if patients are having a lot of forearm flexion weakness, um,

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it's likely the median nerve is a culprit.

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You can see that the deeper flexor muscles are innervated by that, uh,

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anterior interosseous nerve branch, uh,

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which we just kind of shorthand the a i n

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now more radially or laterally.

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In the forearm we have the radial nerve depicted in green and we again have a

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major superficial in a deep motor branch.

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The deep branch runs just posterior to the posterior interosseous membrane or to

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the interosseous membrane.

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And so we call it the pin or the posterior interosseous nerve.

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And here's a depiction of the corresponding muscles that are innovated by the

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radial nerve. Um,

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and you can see that it's predominantly the forearm and hand extensors, uh,

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with the more distal extensors being intr innervated by that posterior

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interosseous nerve branch. The more proximal extensors,

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as well as some of the muscles that cross the elbow joint innervated by the

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radial nerve proper.

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And the third major nerve in the forearm is the ulnar nerve. Uh,

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the ulnar nerve runs along the medial or ulnar aspect of the elbow in the

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forearm and into the anter medial aspect of the kind of muscle bulk

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there.

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And you can see that the ulnar nerve is also responsible for innervation of some

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of the flexor muscles, uh,

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specifically the flexor digitorum profundus and the flexor carpi ulis. Uh,

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you can see that it's more on those ulnar sided portions of the forearm flexion

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that are not invaded by our median nerve.

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And finally we'll get to the level of the wrist here, two major nerves.

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The median nerve, which we see within the carpal tunnel depicted in yellow. Um,

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the median nerve, uh,

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is predominantly involved in innervation of the thenar muscles of the,

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of the thumb and hand. And finally, the ulnar nerve.

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And the ulnar nerve is outside the carpal tunnel and innervates the remainder of

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the hand muscles that includes, uh,

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the intrinsic musculature as well as the hypo thenar musculature.

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All right,

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so why am I spending so much time reviewing all of these muscle innervations and

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whatnot? Um,

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well in most of these cases I'll tell you it's the changes to the muscles that

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are apparent on imaging. So when we're evaluating the muscles,

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we're looking for denervation changes and that can include edema and atrophy.

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And once you can identify the pattern of muscle change,

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it really helps guide the search for the corresponding nerve abnormality.

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So instead of evaluating all of the nerves and all of the muscles,

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I like to start with that kind of pattern of denervation or pattern of

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involvement and then go back and scrutinize the nerve.

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So I'll start by screening our fluid sensitive sequences and then I will go back

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and identify the primary nerve and see if there's abnormality there.

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So you're gonna see a lot of short axis or axial sequences in this case set,

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and that's because, uh, one,

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you wanna be able to use the other nerves and muscles as normal internal

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comparisons. And two, you don't wanna just see the nerve on one slice,

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you wanna see it on multiple slices.

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So you can identify any caliber changes or any signal changes.

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So when evaluating these cases,

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the T1 is really great for looking for the nerve anatomy, the nerve location.

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There's normal perineural fat around the nerves,

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which is T1 bright and helps us identify the location of those nerves.

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The fluid sensitive, again,

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is great for identifying the pattern of muscle abnormality, uh,

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which can help guide your search and post contrast sequences.

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There's a few in this case set. Um,

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they are a must when you're evaluating for tumor or infection.

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They may increase the conspicuity of an abnormality,

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but not necessary in all cases. So, all right,

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let's go ahead and look at some cases.

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I'm gonna show you these as an unknown while I'll give you a little bit of

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clinical history. I'll give you a moment to kind of, um,

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evaluate these images because they can be subtle findings.

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So this first case, this is a 41 year old woman.

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She had some shoulder pain after she had been doing some weight lifting and she

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had some weakness of her shoulder girdle muscles.

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I won't give away the fun and tell you which ones quite yet.

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So we have a T1 weighted sequence on the left and on the right we have a

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somewhat smaller field of view, um, PD fat sequence, or I'm sorry,

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it's a coronal T2 sequence.

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And we're gonna go from lateral to medial here. Scroll through one more time

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and then I have a few more imaging planes.

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So switching to our coronal plane, again,

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T1 here on this side and fluid sensitive coronal sequence here

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and going from posterior to anterior.

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And you're all probably getting the idea here.

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So we'll just do an axial sequence, PD fat set for completeness sake.

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And then we'll switch over to our first multiple choice question.

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All right, in our first polling question,

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what is the most common cause of nerve entrapment about the shoulder? Got four,

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uh, options there. Traumatic transection, paralabral cyst, neurogenic tumor,

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or an anomalous muscle. All right,

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and everyone, a hundred percent, very well done. So paralabral cyst,

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by and far the most common, uh, this is hopefully a good warmup case,

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something that you have seen before. Uh, as I mentioned,

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it's frequently tested on because the pattern of denervation is very

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predictable. Uh, so remember that our nerve courses, uh,

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through first that sup scapular notch,

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it gives off a branch to the supraspinatus muscle,

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then goes to the spinal glen edge, not notch,

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giving a branch to the infraspinatus. Uh,

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and so if you have more distal impingement,

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you may just have infraspinatus muscle involvement.

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If you have more proximal impingement,

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it's likely that you'll have involvement or denervation of both the

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supraspinatus and infraspinatus.

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So I'm gonna go back to our case here and just share a little bit of, uh,

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those imaging findings and make sure, uh, everyone identified them. So again,

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starting with our fluid sensitive sequence,

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using other muscles as a normal internal comparison,

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you can really appreciate the increased signal,

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even some fatty infiltration or atrophy of that infraspinatus muscle.

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And when

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We're comparing that to the other muscles in the shoulder girdle,

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we can see that this is much brighter and has more fatty infiltration than the

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other muscles, uh, of the rotator cuff specifically.

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And as we become more medial and we kind of identify a cause, uh,

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pretty quickly, or I'm sorry, more lateral here,

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and we see this large cystic structure,

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it's right along the course of our spino glenoid notch.

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So now we have a a cause we have kind of the secondary changes of muscle

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denervation and it's right along the course of our superscapular nerve.

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Remember through the supraspinatus notch adjacent to the spinal glenoid notch.

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And that's where it gets impinged. In fact,

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you can see the nerve pretty nicely right here. Um,

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the same findings you can are present on the coronal sequence. Again,

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great way to kind of look for the internal comparison of normal muscle signal to

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abnormal muscle signal.

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We have our paralabral cyst pretty large in this case,

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and most paralabral cysts caused by a labral tear obviously.

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So we have some abnormal signal of that superior posterior labrum.

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I think we can really appreciate that the cysts are rising from that region of

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labral tear here in the superior posterior shoulder.