Ultrasound in Neuropathies: Showing How it Explains the Symptoms and Signs - HD

Introduction

Hi, I am Dr. L Nazarian. I'm professor of Radiology and Vice Chairman for Education at Thomas Jefferson University Hospital in Philadelphia, Pennsylvania. I have an expertise in musculoskeletal ultrasound, and over the past few years, nerve imaging has become more and more important in our field.

Today I'm gonna talk to you about the ultrasound evaluation of the peripheral nerves.

Scenarios in Nerve Ultrasound Imaging

There are different scenarios in nerve ultrasound imaging, and it's important to keep these scenarios in mind in order to understand what we're contributing to patient's care by doing the ultrasound of the peripheral nerves.

The first scenario is when the clinical assessment and the ultrasound are both positive, the ultrasound can be very helpful in confirming a clinical diagnosis of a neuropathy. It can also show the anatomy, is it a nerve injury, mass entrapment, et cetera, that helps to guide further treatment.

The next scenario is when the clinical assessment is positive and the ultrasound is negative. In these situations, ultrasound may alter the management decision. For example, it may show that a nerve release or nerve exploration is unlikely to help.

The next scenario is when the clinical assessment is equivocal and the ultrasound is positive. Here is the situation where ultrasound helps clarify the pathology and make and increase the confidence that there's something actually wrong.

And then when the clinical assessment is equivocal and the ultrasound is negative, it's the opposite. Ultrasound may increase confidence in ruling out pathology.

The next scenario, which is actually fairly common, is that ultrasound sees an incidental finding. It may see contralateral disease that is not yet presented clinically, or it may find a finding completely unrelated to why the patient was referred.

Scanning Techniques

Now, in scanning nerves, as in most musculoskeletal structures, we try to use high frequency linear transducers, and these should be generally at least 12 megahertz. And as we know in ultrasound, the higher the frequency, the better resolution, but less the penetration.

So if we are examining a deep nerve such as a sciatic nerve in the thigh, we may need to go lower than 10 to get the penetration. But certainly for superficial nerves, if you go at least 12 megahertz or more, you're going to see the optimal resolution.

Now, one of the very important parts of MSK ultrasound in general and nerves are no exception, is that we have the contralateral side for comparison. This helps differentiate normal for abnormal because there's such a wide range of nerve sizes in different individuals. And so it's important to be able to compare the other side.

Just beware of bilateral pathology, because one side may be symptomatic, the other side may be asymptomatic, even though the pathology is on both sides. So that's something just to be aware of in bilateral comparisons.

Nerve Anatomy on Ultrasound

Now, what are we actually looking at? Peripheral nerves are made up of nerve fascicles that are separated by connective tissue. And when we put a really high frequency ultrasound on the nerve, we see those fascicles show up as these dark areas, hypoechoic areas, almost like a bunch of grapes, which are separated by the hyperechoic connective tissue.

And just for comparison, this is an overlying tendon, and you can see that compared to a tendon, the nerve has what we call a fascicular pattern, whereas the tendon has a fibrillar pattern where the fibers of the tendon are more compact and they look different from a nerve.

If we go into the long axis view, again, we can see the comparison of the tendon in the near field where it's compact fibrillar pattern, and then the more fascicular pattern seen of the nerve deep to it.

Clinical Scenarios

I'm gonna run through various clinical scenarios and show how ultrasound imaging can be useful.

Median Neuropathy

The first clinical scenario is a patient who has signs and symptoms of median neuropathy. Now, most of the median neuropathy that we see has something to do with the carpal tunnel, and this is a diagram of where the probe is placed to image the carpal tunnel as well as showing the anatomy.

So the large arrow here is pointing to the median nerve, and then we can see the transverse carpal ligament, also known as the flexor retinaculum. Superficial to the nerve, deep to the nerve, we have the superficial and deep flexors of the wrist on this side. On the radial side, we have the flexor carpi radialis tendon and the scaphoid bone. On the ulnar side, we have the pisiform bone, and then we have the ulnar artery shown here, and then the ulnar nerve as shown here.

So the ulnar nerve is not within the carpal tunnel, however it is, it can be seen on the same view that we used to image the carpal tunnel.

A normal variant to be aware of is the bifid median nerve. We may see the median nerve not as one, but as two structures. And these two components can be equal in size or they can be a little bit unequal as they are here.

The other thing to be aware of is that when you have a bifid median nerve, there's often an artery in the middle called the median artery, which is not a normal, typical artery to have. But if you have a bifid median nerve, it's often, there's often an artery in the middle and it has flow within it. So if you're considering any interventions, it's important to know that that artery exists.

Now, carpal tunnel syndrome ultrasound criteria have been extensively reported in the literature. And the biggest parameter that we use is the cross-sectional area of the median nerve at the distal wrist crease. That is right before the median nerve enters the carpal tunnel.

Because what happens is that when the median nerve or any nerve for that matter is compressed, it will swell up proximal to the side of compression criteria can be either absolute or relative. In other words, there are articles that say that a certain number is abnormal. And then there are articles that show a comparison of numbers, is what it's abnormal.

But when people use absolute numbers, most papers will say that up to 0.09 square centimeters, or if you prefer nine square millimeters. So they're the same thing, is normal greater than 0.12 square centimeters is abnormal. And then 0.09 to 0.12 is the gray zone where it may be either normal or abnormal.

And then there are other signs we can use, of course, which is thickening of the retinaculum and flattening of the median nerve within the carpal tunnel.

Now, the new criteria, of course, they're now eight years old by now, but new compared to the criteria, we still start, we initially started using, were in a paper published in radiology where they looked at a hundred wrists in 68 patients. They compare it to clinical and EMG as their gold standards.

They measured the median nerve at the proximal third of the pronator quadratus, and they measured it at the carpal tunnel, and then they subtracted one from the other. And if that difference was greater than 0.02 square centimeters, it was extremely sensitive and specific for carpal tunnel.

The value of this paper is that since people can have different size nerves by using a relative measurement in the same patient, you can say, if the nerve gets more than 0.02 square centimeters, bigger as it goes distally, that's abnormal and diagnostic.

So this is, these are criteria that have been adopted by many people as this relative, these relative criteria.

How do we measure the nerve? Well, essentially, every ultrasound machine has some way to do this with an ellipse function or with a free drawing function where you can just trace with the cursor around the nerve and we get a cross-sectional area of the nerve that reads out. And here it reads out to 0.08 square centimeters, which is within the range of normal.

As we compare it to this individual who had clinical carpal tunnel syndrome, you can see that the measurement is 0.28 square centimeters, which if we use the absolute numbers, I told you up to 0.09 is normal. So this is essentially three times the normal size of a median nerve, and that is indicative of carpal tunnel syndrome.

We can then go on and look to see what is causing it. So we then go into the long axis, and in this situation with proximal on this side of the screen and distal on this side of the screen, we can see that the nerve comes, it gets narrowed under the thick transverse carpal ligament and then gets big, although not as big as it was before the area of narrowing.

Here's the flexor tendon underneath it, just for comparison. So abnormal echogenicity, it's hypoechoic, and it has this swelling proximal to the area of compression. And that's diagnostic of what we see in carpal tunnel syndrome.

This is an even more severe case with 0.35 square centimeters, just a quite huge median nerve. And if we look longitudinally on this one, we can actually see that the nerve gets so compressed under the transverse carpal ligament. We can hardly even see the nerve at all at somewhere the arrows are showing.

Now, one of the very useful things about ultrasound for peripheral nerve imaging is that we can trace a nerve and see where along its course. The problem is, if you're doing an MRI, you're sort of limited to one field of view, but with ultrasound, you're not, you can take the probe and you can just basically trace along the entire median nerve.

So this was a United States soldier who was shot in Iraq and had a complete median neuropathy. The MRI was not very helpful. He had a lot of metal that was distorting the MRI image. And so by tracing along the median nerve, we were able to see this area between the arrows, where the median nerve, we could see it here, we can see it there, but unfortunately there was a gap right there, which was where the nerve got severed.

Now, now luckily this was soon enough after the injury and the examination was clear enough that the surgeon could then go ahead and try to repair that nerve.

Also, ultrasound can show other findings in carpal tunnel syndrome, for example, remember that there are also tendons that live in the carpal tunnel. So here's an example where the nerve was relatively normal, but when we put the color doppler on, we just saw a lot of flow in the underlying tendons.

So this is a tenosynovitis or inflammation of the tendons in the carpal tunnel, which was causing the signs and symptoms of carpal tunnel syndrome.

So why is this important? Well, if this patient was going to be taken to surgery to release the median nerve, that would not have worked because that is not the problem. The problem is not with the nerve problems with the underlying tendons.

So this fits in that category of somebody who has the positive clinical diagnosis, where ultrasound really defines the anatomy. And in this case tells you that it's really not the nerve, it's the underlying tendons that are the problem.

This is another example just to illustrate why it's important with ultrasound, that you can trace the entire nerve. This patient had a median neuropathy and a history of neurofibromatosis tracing the median nerve showed these hypoechoic nodules along the length of the nerve.

In fact, here's a little video. And you could see as we come along the median nerve, which is in here, there's one nodule, another nodule, another tinier nodule, and another nodule as we come down the nerve.

So basically there are multiple nodules studding the nerve. And so this was very important to understand why the patient had median neuropathy. And again, where would you do the MRI? Would you do it of the wrist? Would you do it of the elbow? I mean these, the median nerve goes through the entire upper extremity.

So it's very important to be able to trace the entire nerve on ultrasound.

Now, most of the time when the median nerve is compressed, it is compressed at the level of the carpal tunnel. But there is a syndrome called pronator syndrome where the nerve is compressed at the level of the elbow instead of at the level of the wrist.

Here's such an example. PT stands for pronator teres muscle proximal is on our left distal on our right. So here we see the nerve that's large, large and then narrows underneath the muscles. And that is a site of compression.

Again, not as common as the carpal tunnel, but pronator syndrome is what it's called. And it's something to look out for, especially in patients who are sent to you and you're told that their EMG was positive for the median nerve, not at the wrist, but higher up toward the elbow.

Now, there is an entrapment syndrome of one of the branches of the median nerve that's important, which is the anterior interosseous nerve. This nerve is difficult to visualize directly 'cause it's very small, but it does cause atrophy of the muscles in a classic pattern. And by looking at that pattern, you can infer that there's something wrong with the nerve.

This nerve supplies the pronator quadratus flexor digitorum profundus and flexor pollicis longus tendons. So this is how we mainly diagnose this condition. Occasionally you can see the nerve. This is one example where we actually could see this very small, basically a millimeter size nerve that suddenly came to a point here, but that's not the norm.

The norm is that we're gonna look for the patterns of muscle atrophy. So here is a side to side comparison on a split screen with the right upper extremity and the symptomatic left when muscles atrophy, they fill with fat and they become brighter and then they become thinner as well.

But the first step is as they fill in with fat, they'll become brighter because of more interfaces. So we could see that this is the pronator quadratus muscle on the left side and the normal side for comparison. See how much brighter the muscle is on the left, and that should immediately make you think that the patient may have entrapment of the anterior interosseous nerve.

Here's a patient who had anterior interosseous nerve entrapment, who again, this is a long axis to the pronator quadratus the normal side for comparison in this patient, not only was it brighter, but it was also thinner than the other side as well showing that that muscle was atrophying.

And again, there are two other muscles that can also atrophy in this condition. So this would be the normal side with the flexor digitorum superficialis and profundus muscles, and then the symptomatic side with the superficialis looking intact. But the profundus looking too bright because it's atrophic.

Remember, nerves nourish muscles, so if the nerve is abnormal, the muscle will often become abnormal as well. And then finally we have the flexor pollicis longus muscle flexor of the thumb, normal side, abnormal side, brighter and thinner.

Now, how can this be helpful clinically this is a 61-year-old woman and she could not actively flex her first and second DIP joints after she had a wrist injury. So she saw a surgeon who sent her for an ultrasound to quote, localize the site of rupture of the flexor digitorum profundus and flexor pollicis longus.

But immediately when I see this combination of muscles being mentioned, we have to think, maybe it's not really actual tendon rupture. It could actually be a muscle problem. And in fact, the tendons were intact. Here's the compact fibrillar pattern of the flexor digitorum tendons. And those were fine, but what was abnormal were the muscles.

So if we have the muscles here labeled on the symptomatic right side and the left side, we can see that both the flexor pollicis longus and the flexor digitorum profundus muscles were significantly thinner than on the normal side. Notice that the superficialis was relatively the same, but again, this pattern should make you think of anterior interosseous nerve entrapment.

And then immediately we went to the pronator quadratus so that that was thin and bright as well. Diagnosis is now made.

Now in the antecubital fossa, not only do we have the median nerve, but we have some other smaller branches that can be important as well. This was a 70-year-old woman who had severe pain after a blood draw, and the pain just did not go away.

So, with this kind of history, you're going to first look for the vein that they were trying to draw blood from. So here's that vein. But now we're gonna look did they actually do something to one of the surrounding nerves?

And sitting right next to this vein was a nerve that was way too large to be a nerve in that area because usually those are cutaneous nerves and cutaneous nerves are quite small. And in fact, when we were able to trace it, we saw it was the lateral antebrachial cutaneous nerve and you could see the nerve coming down normal, normal and then fatty swelling right at the level of the needle stick.

So we're able to diagnose that this was a nerve injury related to the blood draw.

One of the beauties of ultrasound then is we don't have to just stop with making a diagnosis. Now that we have the abnormal anatomy laid out, we can go ahead and do an intervention. In this case, we did a perineural injection. Here's the needle coming through and the medicine being injected around the abnormal nerve.

And fortunately she had very significant relief in her pain from that injection. So it was a very nice outcome.

Ulnar Neuropathy

Moving to the next clinical scenario, patient who has signs and symptoms of ulnar neuropathy.

So just to review some anatomy here, the ulnar nerve at the distal humerus passes in a ring that's formed by the medial epicondyle, the medial collateral ligament, and it's bridged by a retinaculum called Osborne's ligament. So that's what covers the nerve within the cubital tunnel and the probe is placed as shown to get that image.

If we then go into the longitudinal axis, we have the drawing of the nerve coming through this way and it should also be noted that more distally the nerve enters into a tunnel between the ulnar and humeral heads of the flexor carpi ulnaris muscle. And these are connected by a ligament called the arcuate ligament.

So this anatomy can all be seen with ultrasound. So the ulnar nerve at the elbow, here's the longitudinal view. So here it is coming down and across the elbow and long axis.

Now similar to with the median nerve, we can get cross-sectional area measurements to determine whether this nerve is abnormal or not. This is the normal left side for comparison.

This patient had a severe ulnar neuropathy with numbness and tingling in the fourth and fifth digits, as well as weakness of those digits. And we can see that the nerve on the symptomatic side is almost four times the size on the asymptomatic side. And that tells you that that is likely to be the cause of the patient's symptoms.

Here's another patient who also had an enlarged nerve. And notice not only is it bigger and we usually use 0.09 square centimeters as a rough guideline for this nerve as well. Not only is the nerve bigger on this side, but we can also see that it's lost its fascicular pattern.

Now the next thing we can do is go on and try to trace this nerve and see where the site of pathology is. Well, from that diagram I showed you, the nerve passes under that arcuate ligament, which connects the two heads of the flexor carpi ulnaris.

And as the nerve is coming down to the ligament here, you can see that it abruptly changes caliber right at that level. And that's very similar and reminiscent to what we saw in the carpal tunnel for the median nerve and the flexor retinaculum. But in this case, it's the ulnar nerve being compressed under the arcuate ligament.

These cubital tunnel syndrome cases can be quite abnormal and there's a very, very large ulnar nerve. Again, though tapering abruptly at the level of the arcuate ligament.

Another beauty of ultrasound is it can show you pathology not necessarily expecting. So this patient, it was thought to have classic cubital tunnel syndrome, but actually the patient also had severe rheumatoid arthritis and the ulnar nerve was not abnormal size.

The problem was that it was being pushed by this tissue, which turned out to be rheumatoid inflammatory tissue or pannus that was pushing out from the elbow and displacing the ulnar nerve. And that's what was causing the ulnar neuropathy. Again, important to know because the treatment is obviously very different.

Now, another entity that we'll see with the ulnar nerve is ulnar nerve subluxation. This is seen when you flex the elbow and occurs in about 15% of normal individuals. That is patients with no symptoms at all.

And as I'll show you in a minute, it's important to differentiate from another condition called snapping triceps syndrome. So what happens in ulnar nerve subluxation, what happens is that the nerve, normally when you flex the elbow, it should stay behind the medial epicondyle.

However, in ulnar nerve subluxation, the nerve heads this way, it heads over the epicondyle and then it perches on top of the bone as shown again, that that occurs in about 15% of normals, but it can be a cause of symptoms.

So here is the ulnar nerve and there's the medial epicondyle, we'll put the video in place. Here's the nerve coming up and over the medial epicondyle. And so that shows you, and I'll play it again, shows you what we call ulnar nerve subluxation.

Again, normal individuals can have this, but it can also be a cause of symptoms such as in this patient who had a very large ulnar nerve shown here in extension. And then with flexion, this whole big ball of nerve came up and over the medial epicondyle and that shows you ulnar nerve subluxation.

But in this patient it was also likely to be contributing to their symptoms.

Now a mimicker that I just like to put in here because this entity, if you miss it, the patient will be treated improperly. It's called snapping triceps syndrome. And snapping triceps syndrome not only does the ulnar nerve subluxate, but also the triceps muscle, the medial part of the triceps muscle also subluxates.

So I'll play you a video. You're gonna see first the ulnar nerve come over and then with it comes the triceps.

Why is this important to differentiate? Because if you just move the nerve surgically and you do not treat the snapping triceps, the patient may say, wait a minute, my painful snap is still there. You didn't do anything to treat me.

Well, that's because you've gotta know. The surgeon needs to know that if the triceps is also causing symptomatic snapping, then you need to resect a piece of the triceps, otherwise the patient is not going to get the recovery that they are looking for.

Now, not as common as problems at the elbow. The ulnar nerve can be compressed at the wrist. The anatomic diagram I showed you earlier shows that when you look down at the wrist, you can see the pisiform bone and you can see the ulnar artery with the ulnar nerve lying between the artery and the bone.

And that nerve can be entrapped within so-called Guyon's canal. So there is the long axis of such a patient. Usually when the nerve comes down it just tapers very gradually. But in this patient it tapered pretty abruptly and had a positive Tinel's sign.

That is when I tapped over this area, it totally produced the patient's symptoms. And so the imaging finding plus the physical exam finding made the diagnosis just as a little aside here, none of these diagnoses should be imaging alone. You always need to take the clinical examination into account before you make any of these diagnoses.

Radial Neuropathy

So now let's move to the next clinical scenario. Signs and symptoms of radial neuropathy.

This case taught me early on in my career how important nerve imaging was in this patient who had a complete wrist drop. But we had a frustrated neurosurgeon on our hands because they did an MRI and the MRI was equivocal and they couldn't really tell him where the lesion was.

You can tell the image quality is not as good as with some modern equipment 'cause this was many years ago. But what I did was basically traced the radial nerve and lo and behold, there was a mass involving the radial nerve. This was about midway in the arm.

And so I called the neurosurgeon, he said, how am I going to see this? And I said, let's come to the OR and show you. So we went to the OR we made an X marks the spot and there's the neurosurgeon exposing and showing the mass involving the radial nerve and it turned out to be a neurofibroma over the radial nerve.

And so this is the first case that really taught me how important it was when you have a patient with a neuropathy to be able to follow that nerve and see exactly where the site of problem arises.

Now there's a very important branch of the radial nerve called the posterior interosseous nerve. It's actually more properly called the deep motor branch of the radial nerve until it pierces the supinator muscle and then it becomes the posterior interosseous nerve.

But most in common usage, most people will interchange posterior interosseous nerve and deep motor branch of the radial nerve.

When this nerve is entrapped, it presents with motor weakness in the extensors of the wrists and or fingers. And it may have pain and tenderness that mimics lateral epicondylitis because it turns out the location of this nerve is not far from the lateral epicondyle, it's just located more medial to it and sort of in the substance of where the supinator muscle lives in the upper forearm.

And that's what makes you think, maybe this is this problem and not lateral epicondylitis.

Now ultrasound has been very useful in the differential diagnosis. This is a case report we did many years ago, and actually we'll show you images from that case report.

So the normal posterior interosseous nerve, this is a longitudinal view of it, it's very small, it's only about a millimeter. And as it comes down, it pierces the two heads of the supinator labeled s and s right over here. And it has a nice smooth taper in the short axis.

The nerve looks like a flat pancake like this and that's the normal situation. But we've seen this recurring theme of when nerves are compressed, they swell up behind the site of compression.

And here's what happened in this one patient who had a misdiagnosis of lateral epicondylitis for a long period, in fact, she had to go on disability, but an astute neurologist in our area said, wait a minute, I think we need to take a look at the posterior interosseous nerve.

And sure enough, this nerve was swollen like a sausage, and then when he tried to follow it into the supinator, you could hardly see it anymore. So this was basically a trapped nerve.

When we looked in the short axis, the nerve had more of a rounded appearance rather than the flat appearance on the normal side.

This patient went on to have surgery to release the trapped nerve and it, this is after release, the nerve still looks a little bit swollen, but what's most important is that the nerve now has a lot of room to travel. It's no longer compressed within the supinator.

And of course, more importantly, the patient was completely asymptomatic and was more than happy just to come in to let us get a picture of her arm so we could use it and publish it because she wanted more people to know about this condition.

And it is a condition you should definitely think of when patients present with lateral elbow pain.

Lateral Thigh Pain and Numbness

Okay, so now our next clinical scenario is lateral thigh pain and numbness and a history of total hip replacement.

We often can see lateral thigh pain and numbness in a condition called meralgia paresthetica, which is a term given to a problem with the lateral femoral cutaneous nerve.

This nerve can be identified by looking at the anterolateral aspect of the sartorius muscle in the upper thigh. And without going into great detail about the anatomy, this was this particular patient who had had this neuropathy after hip replacement. And this nerve was absolutely huge.

I mean this is, should be a very tiny difficult to see nerve and in the long axis we can see the nerve is quite enlarged and then it only tapers to normal quite distally. So this was a nerve that was injured during the hip replacement surgery.

And so again, we have to use the real time advantage of ultrasound and we're able to stick a needle around that nerve and able to inject some local anesthetic and cortisone, which gave him some temporary relief. He eventually went on to have alcohol ablation of this nerve with very, very good results. Again, I'm using ultrasound guidance.

Now this is another patient who presented with a femoral neuropathy after a total hip replacement. So rather than having the lateral hip and thigh pain like we had previously, this patient literally could not move his quadriceps muscles, could not extend his knee.

And when we looked, we saw that there was a large mass sitting within the pelvis. And when we looked carefully, we realized that between the arrow heads here was the femoral nerve and where the arrow is is the iliopsoas tendon.

So this is a very large iliopsoas bursitis that occurred after hip replacement and this was causing femoral neuropathy because this was not really fluid that could be easily aspirated. This patient actually had to go on and have this resected. So it's actually surgically removed to release the pressure on that femoral nerve.

Sciatic Neuropathy

Okay, our next clinical scenario is sciatic neuropathy. Now the sciatic nerve is deep and difficult to see, so we don't have a lot of role for ultrasound here.

But just to show some illustrative cases, this is a patient who had a plexiform neurofibroma of the sciatic nerve MRI, just to show that like any other nerve mass, we can see it well on ultrasound, which we know where to look and where to trace the nerve.

You can see this multilobular hypoechoic appearance and this hypoechoic appearance is very typical for nerve masses wherever we happen to see them.

But the other very useful point for sciatic nerve is to look for injury to the nerve. The sciatic nerve can be cut during surgery. The classic surgery that may be cut during is surgery on the hamstring tendon.

This was a young woman who had hamstring surgery and after surgery had absolutely no function of her sciatic nerve and she was no longer able to walk. So the surgeon was really of course concerned that something had happened to the sciatic nerve.

So when we looked we could see nerve fascicles here and nerve fascicles here. But then we saw this sort of amorphous hypoechoic material and when we looked carefully, we realized that hypoechoic material was a hematoma and that the arrowhead, the cursors here were separating what was a transected or torn sciatic nerve.

Obviously a real problem, but ultrasound was really critical here in showing where the nerve was torn and how far the edges were separated from each other.

Peroneal Neuropathy

Moving on to lower in the lower extremity, we often see patients with peroneal neuropathy, which can present with foot drop and or numbness and tingling and pain going down the lateral aspect of the leg.

The normal peroneal nerve can be identified by placing the probe in the axial plane, finding the echo of the fibula and then going just posterior to that. And that is the normal common peroneal nerve also called the fibular nerve.

Here's the long axis showing the common peroneal nerve and long axis, which is nice fascicular pattern and as it continues to come down, it will cross over the head and neck of the fibula and then it'll divide into the superficial and deep branches into the calf.

Here's such an example though, where the nerve, rather than being flat as I just showed you, normally was actually rounded. And when we went into the long axis, we saw a normal nerve, then it started to enlarge, then it got quite large and then it got small again right at the level of the fibular neck, not on this image, but this was the level of the fibular neck.

And so this was a patient who had peroneal nerve entrapment at the level of the fibular neck. We were able to tell the surgeon that release of that area would likely give the patient symptomatic relief.

Other pathologies that can occur, the peroneal nerves at that level, you can have a ganglion cyst that arises from the joint between the proximal tibia and fibula and then can literally grow into the nerve. This is an MRI of such a patient.

And then the corresponding ultrasound showing that there's a ganglion cyst and here's the nerve fibers and the cyst has sort of insinuated itself amongst the nerve fibers and this is what's causing a foot drop.

And this patient. Now, the beauty of the ultrasound in this situation is we could stick a needle and we did stick a needle into that ganglion and we aspirated it and that immediately took the pressure off the peroneal nerve.

But of course we never know what to expect. So this is somebody who had peroneal neuropathy. If after a motor vehicle accident we were absolutely expecting to see a nerve injury, but instead as we followed the nerve down, we actually saw a mass arising from the nerve and had a lot of, here is a extended field of view showing the mass, the mass was kind of wrapping around from side to side.

We're thinking is this just a hematoma? Is that what we're seeing here? What's going on? This had a lot of irregular flow within it.

So this was somebody who just happened to traumatize a preexisting tumor on their nerve when they had a car accident and the symptoms arose at that point.

But just to sort of hit home the point of why it's so important to be able to follow the whole extent of the nerve and then use all the tools at your disposal, the grayscale appearance and color doppler to help characterize what you're looking at because without color doppler, you may have just thought that this was an amorphous collection of blood from the trauma, but no, it's actually a vascularized neoplasm.

This was somebody who had a lesion removed from the skin and then immediately had foot drop afterwards. And so we were following the peroneal nerve down and there was this area here that just did not look right and as we continued to look, we went superior to the incision.

Okay, we could see the fascicular pattern. Then as we came inferiorly it looked like that fascicular pattern was essentially cut in half by a suture that was thrown right through the nerve. So part of the portion of the nerve was in the near field part, it was in the far field.

So this was somebody who had a suture thrown through their peroneal nerve causing foot drop. If you MRI this patient, you would not be able to see this pathology most likely because the resolution is so much greater with the ultrasound and you certainly wouldn't be able to see the suture material that we could actually identify as bright little echoes.

And so really shows you the value of the high resolution of ultrasound here.

Here's somebody who had a superficial peroneal nerve neuropathy where they had numbness and tingling in their foot and they had a little bit of peroneus muscle that was herniating up and pushing on the nerve, causing it to swell more proximally.

Again, a pathology that would be very difficult to see any other way, but we could confidently say to the referring clinician that this was a focal peroneal neuropathy caused by bulging of the muscle, a so-called muscle hernia pushing on the nerve.

Tibial Neuropathy

Now how about the tibial nerve? Remember just for review, the sciatic nerve divides into the tibial and peroneal nerve. So we just talked about peroneal neuropathy. Now we'll talk about tibial neuropathy.

So the tibial nerve, like any other nerve, has this particular pattern. This is somebody who had tibial neuropathy. This is the normal side and then the abnormal side for comparison, we have a mass arising eccentrically from the nerve when we see that, that implies that that's a nerve sheath tumor and that's what this was.

And often when you do see a soft tissue mass, it's imperative to look to see whether there's a nerve entering and or exiting the mass. So in this situation, we saw the mass first before realizing that it was a nerve issue.

It had some through transmission, but through transmission does not help you with cystic versus solid in the superficial tissues because many solid masses have through transmission. In the superficial tissues it was hypoechoic, a little bit heterogeneous.

But the key finding here is that there was a tubular structure going in and a tubular structure going out that was not a vessel. And so it's a nerve. And so that tells you that this is a nerve mass.

And knowing where we were on the body, this was a tibial nerve mass turned out to be a schwannoma at surgery.

This was a patient who had loss of plantar flexion after a calf laceration. And so there was a large wound here, which was cutting right through the muscle and the surgeons knew that. But what they really needed to know too though, is where was the nerve?

Because they were gonna fix the muscle, but they did not know where the nerve was, how severely it was injured, where were the edges of the nerve.

Here ultrasound comes to the rescue because we can see the proximal end of the tibial nerve and the distal end of the tibial nerve and we can measure exactly the distance between the two. This then told them that they were not going to be able to make a primary repair of this nerve 'cause the edges were too far apart.

So they knew that they'd have to take a nerve graft in order to fix this nerve, which is what they did. And the ultrasound here critical in telling them what's going on.

Now, when the tibial nerve is symptomatic within the ankle, it gives rise to so-called tarsal tunnel syndrome. And tarsal tunnel syndrome is unlike carpal tunnel syndrome in that we rarely see the nerve compressed under a ligament like in carpal tunnel syndrome.

Most commonly if we see something in tarsal tunnel syndrome, it's usually an adjacent vessel or ganglion or other kind of mass or a tendon problem that is causing it.

So this is such a case in somebody who presented with tarsal tunnel syndrome and what we saw was an artery that was wrapping around the tibial nerve. There's the nerve there and to prove it was an artery, here is the doppler and then we doppler it and got an arterial waveform out of it.

And so this was tarsal tunnel syndrome secondary to an anomalous artery wrapping around the nerve.

Here's another different patient who had a ganglion cyst, again pushing on the nerve and causing the tarsal tunnel syndrome. And this is the long axis showing where it's pressing on the nerve. So here's the nerve coming down and you see the nerve narrowing because of the ganglion pushing on it.

So once we see that we can go ahead and offer an ultrasound guided aspiration of the ganglion in order to relieve the pressure on the nerve just like we saw higher up a minute ago in a different patient.

We can also get neurofibromas of the tibial nerve within the tarsal tunnel. And this is such a case. How do we know that's not a ganglion? Well, A, because we could see the nerve coming in and out of it and B, because there was flow on color doppler always a something that should be at your disposal.

Now lest we think that MRI is always the gold standard, this is a cautionary case in that respect. So this was a patient at an MRI for tarsal tunnel syndrome and what they called was a nerve sheath tumor within the tarsal tunnel.

And so the surgeon was gonna take this patient to resect the tumor but wanted to make sure that the tumor was the cause of all the patient's symptoms. So send them to me to ultrasound to have this nerve sheath tumor injected to see whether it would take the symptoms away.

I should also add that this was this MRI was read at an outside institution so that my radiologists at my place rightfully do not get blamed for this. But in any event, our history was injected nerve sheath tumor.

So our sonographer scanned and said, wait a minute, this is the nerve. This is what they saw in the MRI. This does not look solid in any respect. Well, I just showed you a couple ganglion cysts in the tarsal tunnel. Could be that certainly, but in long axis it didn't look like a ganglion because it lengthened out into a tubular structure.

What are we gonna do put on the doppler? And this was a vessel, this was a big vein sitting within the tarsal tunnel pushing on the nerve.

I can only imagine what would've happened if the surgeon went in expecting to take out a nerve sheath tumor and instead there was this big vein sitting there. It would've been not a good surgical outcome in this situation.

Instead, we were able to have not only the neurosurgeon, but also the vascular surgeon both in the OR to make sure that this got taken care of properly. And it did because I saw the patient in follow up and he was doing great.

Miscellaneous Nerves and Conditions

Other miscellaneous nerves that we can see in the lower extremity. The sural nerve is an important sensory nerve that's on the lateral aspect of the ankle and also runs up in the calf as well.

And when patients have surgery or other kinds of trauma, they can develop little neuromas at the tip of the nerve that was cut. So here's a nerve that was cut from trauma and then you could see these little neuromas, these little hypoechoic rounded areas that have grown up on that nerve.

And that is something that we'll see in patients who've had trauma to a nerve. Also called amputation neuromas as well, but they're not always caused by amputation. They can be just caused simply by trauma.

And then a miscellaneous condition that's very important to look at here is Morton's neuroma. Because this is such a common cause of neuropathy in the ball of the foot, it presents with difficulty walking because of pain and numbness, almost feeling that a patient is walking on a pebble.

It can be very annoying. And also it's very common. We look at these with linear transducers, usually in the 10 to 12 megahertz range. I usually place the transducer at the plantar aspect of the foot.

And as I'm scanning plantarly, I take my finger and I compress dorsally. I'm trying to trap the neuroma between my finger and the ultrasound probe.

You can also try the so-called Mulder's test where you squeeze the toes and if you do that, the neuroma will actually go plantarly toward your transducer.

Now Morton's neuromas are fibrosis that occurs around the interdigital nerves, which lie between the metatarsals. So what I've numbered here in the short axis are the third, fourth and fifth metatarsals.

So here we're at the level of the metatarsal heads and the toes and we are looking for Morton's neuromas in between the toes. The most common spaces for them to occur are between toes two and three and toes three and four.

And it's perineural fibrosis, usually from repetitive trauma on the nerve. Patients who do a lot of walking or athletics or who wear tight shoes, high heel shoes are all prone to this.

And so what we can see in this patient is that there's this hypoechoic nodule present between the third and fourth interspace, not present between four and five.

If we go into the longitudinal axis, here's the nerve coming in and then this is the combination of a swollen nerve and thick fascia. That's what we refer to as the Morton's neuroma.

Now how do we tell that that is not just a little fluid collection between the toes? That's when we utilize compression. So here's a video. This is me pushing on that area. Here's the nerve coming into the neuroma.

And you can see that I am not able to press that material completely out. There's a little fluid around it, but there's part of it that does not compress. What that tells me is there's actually a soft tissue mass there. And that's typical for Morton's neuroma.

The patient will often tell you too, oh yes, that's where it hurts. 'cause as you're pressing on the neuroma, they're going to obviously notice the pain.

Now this is the Mulder maneuver that I referred to before. If you're not entirely sure if what you're seeing is a neuroma or not, you can compress the toes together and you'll see the neuroma squeeze out toward the plantar aspect of the foot.

This is a clinical test that's used to diagnose these neuromas because when you squeeze the toes together, it will create pain and we can actually see why it creates pain. Again, because of the motion of the Morton's neuroma toward the plantar aspect of the foot.

Another miscellaneous condition we're asked to look for is myositis. Patients who have diffuse neuromuscular disease or at least have the suspicion of diffuse neuromuscular disease. Muscle changes are very non-specific.

I already showed you bright muscles that occurred in atrophy because of neuropathies. In truth, there are a whole range of processes that cause bright muscles. Inflammation can do it, edema can do it. Fatty replacement can do it, atrophy can do it as well.

So what role does ultrasound have in neuromuscular diseases? Well, there has been good evidence that if you use ultrasound to guide biopsy, you have a higher chance of getting a yield.

So this was a patient presented with pain and weakness in the thigh. And what we have is an extended field of view where we've labeled the quadriceps muscles, rectus femoris, vastus intermedius, vastus medialis, and vastus lateralis.

And so you can see that compared to the other muscles, the vastus lateralis is much brighter and it's lost the normal pennate pattern that we associate with the normal muscle.

So that was the muscle that we chose to have the surgeon biopsy. We can also do percutaneous biopsies, but usually for neuromuscular disease it's nice to have a large piece of tissue to be able to properly diagnose it.

So we can't specifically say what kind of abnormality this is, but what we can say is biopsy the vastus lateralis muscle because it's the most abnormal appearance.

Brachial Plexus

And then finally, another condition I'm just going to touch on because the knowledge of this is growing rapidly and this can almost warrant a separate lecture pretty soon, is the brachial plexus.

So many patients present with problems that occur after the nerves exit the spine and are in the brachial plexus within the neck. And just to show you how well these abnormalities can be seen, this is somebody who had a work related injury and was having pain radiating down the upper extremity.

This is the subclavian artery right above the clavicle. And you can see this bunch of grapes, essentially these very prominent nerve fascicles.

Now is that abnormal for this patient or not? We went to the same spot on the other side and this is what the brachial plexus looks on this side. So obviously markedly asymmetric.

And then when pressing over that enlarged nerve, it produced the patient's symptoms completely. So we were able to diagnose an injury to the brachial plexus on ultrasound.

And again, brachial plexus imaging with ultrasound is a growing field and one which I have a lot of positive feelings about for the future.

Disadvantages of Ultrasound

All right, now let's just go over some disadvantages of ultrasound before we finish. Obviously operator dependence, this is for all of ultrasound and peripheral nerves are no different.

You really need to pay good attention to ultrasound technique, to train your eye, to learn the anatomy, to know artifacts, to know all different types of pitfalls you can fall into.

And so like any other kind of ultrasound, if you're gonna do ultrasound of the peripheral nerves, it's important to learn well and always have an anatomy atlas on hand because you're gonna be asked to look for maybe nerves that you haven't really been asked to look for before.

The other main disadvantage of ultrasound is that it shows form not function. Now what I mean by that is we can't tell how a nerve is functioning by looking at it. That is done clinically and it's done with electrodiagnostic testing. It's not done by ultrasound.

Ultrasound can say that a nerve is swollen, but it cannot tell you necessarily that it's functioning improperly. So that's why it's always important not to rely only on an ultrasound finding, but instead to make sure that you use ultrasound properly, which is in the context of the clinical examination and any electrodiagnostic testing.

Advantages of Ultrasound

Now, what are the advantages? Well, we've already gone over them, but we'll review just all on this slide. Ultrasound is very well tolerated, better tolerated than an MRI in patient surveys, of course, it's significantly lower cost.

It's has better resolution, especially with the high frequency probes that we use for nerve imaging. You're not limited to one body segment. So when you're imaging a nerve, you can go stem to stern on the nerve and look for the pathology.

You can compare it to the contralateral side very easily. This is much harder to do with MRI, but ultrasound, it's just a simple thing, picking up the probe, going to the other side, and you can do real time dynamic studies to look for things like nerve subluxations. As I illustrated to you before.

Conclusion

So in conclusion, when combined with the clinical examination, ultrasound is an excellent tool to depict the anatomic cause of peripheral neuropathies. Thank you very much for your attention.