imaging of the peripheral nerves, and I'm gonna be focusing on MRI. Okay, so here's anatomy of a normal peripheral nerve. We have the axon and myelin surrounded by endoneurium. Multiple axons make up the fascicle, which is surrounded by perineurium. And then multiple fascicles make up the peripheral nerves surrounded by epineurium. And there's a variable amount of epineural fat in the intervening blood vessels. So when the nerve is large enough, such as this cross-section of the sciatic nerve, we can see the so-called vesicular appearance of the nerve with intervening fat and a few tiny blood vessels. So what are we looking for with imaging of peripheral neuropathy? So there are primary nerve abnormalities and secondary abnormalities that affect the muscle. So let's talk about muscle denervation first. So in the acute phase, we see edema-like signal. In the subacute phase, you start to see fatty infiltration. And in the chronic phase, you see atrophy with fatty replacement. And as radiologists, what's very helpful for us in identifying the peripheral nerve culprit is to look at the pattern of muscle denervation. So here, for example, in the forearm, we see denervation of the lateral half of the FTP and FPL, as well as the pronator quadratus. So we know that these muscles are innervated by the anterior intraosseous nerve. And looking further up on the study, we see that the AION is actually hyper-intense and a little bit enlarged. The other important feature of muscle denervation is that when we see it, it correlates with an advanced stage of peripheral nerve injury. Okay, so let's talk about the primary nerve abnormalities, primary signs. So what are we looking for now? We're looking at signal intensity, caliber, the internal architecture of the nerve. Are there any deviations in course? And looking at perineural changes, such as fibrosis. So here's the spectrum. So normal nerves, so here we are above the knee, the tibial and common perineal nerves. Normal nerves appear iso-intense to skeletal muscle. As they become abnormal, they can become hyper-intense. And then enlarged, for example here, as we see with the common perineal nerve relative to the tibial nerve. But we see this fascicular pattern that's maintained. This is a nerve that is more abnormal, so now this is very enlarged, hyper-intense, and we've lost normal architecture internally, so it has a so-called featureless appearance. And further down, this patient has a different kind of distorted architecture in the nerve where there's heterogeneous signal. Lots of perineural fibrosis, we start to see deviations in course, all related to nerve entrapment by all this posterolateral scarring at the knee. And this is a common perineal nerve that's laid out in longitudinal view, and here you see all the signs of abnormality. There's abnormal signal, the nerve is enlarged. There's definitely an internal architectural distortion. There are few deviations in course, and then there's marked perineural fibrosis. So we talked about how muscle denervation correlates with the clinical staging. How about all these peripheral nerve signs that we just discussed, how do they correlate? So we turn to this comprehensive and common classification system that's used as the Sunderland Classification for nerve injury. It goes grade one through five, so in grade one neuropraxia, the nerve is practically normal, just a mild stretch injury. Grade two, three, four, axonotmesis, there's progressive involvement of the endoneurium, then perineurium, and then grade five, there's involvement of the epineurium with a transection of the nerve. And our job as radiologists is really to separate out the grade one, two, three, which require no surgery, because the nerve can regenerate, from grade four or five, which require surgery, because no nerve regeneration is possible. So what does this look like? So in grade one, the muscle is normal, and the nerve is practically normal, or maybe a little hyper-intense. In grade two, three, four, now you start to see more of those signs, and the muscle is definitely abnormal. So now we see muscle denervation. Grade two, we see peripheral nerve hyper-intensity and some enlargement. Grade three, further enlargement, hyper-intensity, maybe some perineural fibrosis, but you see there's this maintained fascicular appearance. In this case, the sciatic nerve around the prosthesis. And then grade four is otherwise known as a neuroma in continuity, so it's a continuous nerve. However, as we saw in the common perineal nerve, this is the ulnar nerve, there's bulbous enlargement, there's disorderly architecture, and there's perineural fibrosis. And these are all the features that we look for to separate out a grade three non-surgical legion from grade four, which is surgical. And then grade five is easy because the nerve is typically transected, and you can get this balled-up end bulb neuroma at the site of transection. Okay, so who comes to MR neurography? Who are the patients that are referred? So it could be the patient with acute trauma, and now your job as a radiologist is really to separate out the surgical candidate from the non-surgical. And in this case, we see a brachial plexus study where we have upper trunk transection, so definitely a surgical legion. But most of the time, the reason people are referred for neurography are to evaluate chronic peripheral neuropathies. And there are 30 million plus people in the United States that have some kind of peripheral neuropathy, more than 100 types have been described, and they all fit into one of these buckets generally, whether it's post-traumatic, metabolic, et cetera. And all of these etiologies can cause either focal or diffuse abnormalities of the nerve. So in our approach to chronic peripheral nerve imaging, or imaging of chronic peripheral neuropathies, then we should think about first, is it a focal or diffuse problem? And if it's a focal short-segment problem, then you want to think to yourself, is it an intraneural intrinsic tumor or tumor-like condition, or is it compression and or entrapment, which you're going to hear a lot about in the next few lectures. So if it's a mess, I'm not going to go into any great detail here. We evaluate with diffusion, IV contrast. There was a whole lecture dedicated to peripheral nerve tumor imaging yesterday, which I hope you saw. And otherwise, we're dealing with compression and or entrapment of a short segment of the nerve. And then I think to myself, is it injury-related or sports-related traction on the nerve or compression of the nerve, in which case you can describe the abnormality and classify the severity, based on what we just discussed with the Sunderland classification. Otherwise, you can think, am I dealing with a known tunnel entrapment, or is there a mass effect on the nerve by an accessory muscle or an adjacent mass? So here's an example of the sciatic nerves, right and left, and this patient has had chronic hamstring injury with lots of scarring. And there's scar tethering or entrapment of the sciatic nerve, which appears enlarged with perineural fibrosis and a relatively maintained fascicular appearance. This is the sciatic nerve now compressed by a sciatic notch hernia. You see the fluid sac and the gonadal vessels going through the hernia sac. And then here's an example of a large perineural ganglion that's exerting mass effects on the obturator nerve, which appears enlarged and hyper-intense. Okay, so if it's not a focal abnormality, then you're talking about a diffuse abnormality, and now you want to describe, am I dealing with a single long-segment mononeuropathy, or are there multiple nerves involved? So what's the role of the radiologist in this scenario is actually, first and foremost, think to yourself, exclude tumor in these scenarios. So here we have an enlarged sciatic going down through the tibial nerve, markedly enlarged, it's pet avid, lots of enhancement. We don't see the normal architecture inside, lots of contrast enhancement. And this is an appearance that's very concerning for a neuro-lymphoma, which is what it is. So you might say, well, could this be sarcoidosis? I mean, yes, it could be, that's possible, but really your job as a radiologist is to inform the referring physicians that you need to go after a malignancy like lymphoma, which can have this appearance. And this is neuro-lymphoma involving multiple nerves with pet avidity enlargement enhancement. So now if you're not dealing with tumor, you've excluded it, now you're left with a long differential diagnosis. And really, the differential can be narrowed based on the clinical history. So is it metabolic, post-traumatic, inflammatory, et cetera? So that's with discussion with the referring multi-D team. And then you also narrow it down based on the pattern of involvement that you see. So for example, here we have a long segment mononeuropathy of the brachial plexus, where we see these alternating areas of constriction enlargement, so the so-called hourglass constrictions that are characteristic of Parsonage-Turner syndrome, and this is thought to be an immune-mediated response. Versus this case, here's another example of, these are 3D T2 MIP images, so the nerves are enlarged, but asymmetrically in the lumbosacral plexus, hyper-intense. And for example, here we have enlargement, hyper-intensity of the right femoral nerve, but not the left, which is normal. And so it's enough for the radiologist to tell the referring team that this is a hypertrophic neuropathy, and then after that, it'll be sorted out as to whether it's acquired or congenital. Okay, so that was kind of a whirlwind discussion here of how to approach the imaging of the peripheral nerves, and we talked about primary and secondary abnormalities that we can see by MRI, and how they correlate with staging of peripheral nerve severity, and then our approach centered around whether we see a focal or diffuse abnormality of the nerve. So thank you very much. Great, thank you. Good morning, everyone. So you will see that Dr. Fayyad and I used to read cases together, because some cases you will recognize. All right, so we'll do another whirlwind through the lumbosacral plexus, and we'll focus on those 11 nerves. Unfortunately not, we only have 10 minutes, so we have to be selective, but the lumbosacral plexus is put together by 11 nerves on each side, and we will start with the obturator nerve, which is fed by the L2 to L4 nerves, typically. There's variations, and it innervates the adductor muscles and the obturator externus, some also say the pectineus muscle, and has medial thigh sensory innervation. So when you want to trace the obturator nerve, you can go backwards or from top to down. This is what we do here, and it's a good idea to start. So this is around L4, and so this is the psoas muscle, and the obturator nerve is formed by L2, L4, and then it runs medially to the psoas muscle right there. So this dot where my arrow is is the obturator nerve, and then it descends down medially to the iliopsoas, then the obturator internus muscle here, and then it goes towards the obturator canal. Sometimes it's better to find the obturator canal and then go backwards, and then it ends in the obturator internus and externus. So what are abnormalities? There are not many. The obturator nerve compression is one that is more common among the rare entities, and here you can see there is an abnormal obturator nerve. So once you traced it, you see there's abnormal signal hyperintensity on the T2 FETSAT images, so here it's important to actually have a T2 FETSAT image. Here's your anatomic image, and here's your contrast imaging, and you can see it's slightly enhancing. Now, the question is what is causing that? In this case, you will recognize this is one that Dr. Fayyad showed. So this is a paralabral cyst that made its way all the way into the obturator canal and started compressing the obturator nerve, and here you have your denervation edema of the adductor magnus down here. The adductor magnus has cross innervation with the femoral nerve, but the obturator nerve, as you can see here, does the same thing. Now let's move on to femoral nerve, also fed by L2 to L4 nerves typically. It has motor innervation to the quadriceps, but also pectineus and sartorius muscles. It has upper and anterior thigh innervation, a sensory through the anterior femoral cutaneous nerve, which it gives off near the groin. So let's review the anatomy. So we start around L3, L4 again. So we have our quadratus lumborum muscle here, and we have our psoas muscle, and we're following one of the L3 nerve roots, and here you can see it is going through the psoas muscle. So this is the one where we have to be careful if we do a trans psoas approach or when the surgeon's put in there in the body grafts. And then where the iliacus muscle and the psoas muscle join, it emerges and then traverses and descends downwards. So this is a patient with a lot of muscle here, but here is the formation of the femoral nerve. It goes all the way down into the groin, and somewhere here it gives off the anterior femoral cutaneous nerve and the motor branch descends down here. So here's some abnormalities to schwannoma of the femoral nerve. So whenever you have a peripheral nerve sheath tumor that has a nice target sign in the center, then that is usually a schwannoma. You can see these on DWI, but also on the other ones. It's more appropriately referred to as schwannoma than neuroma in the periphery. Here is another one where you have a highly abnormal femoral nerve here, thickened hyper intense, and then there's a mass here in the groin. And so this patient had groin surgery and somehow the femoral nerve got nicked and then you can see the profound atrophy and denervation edema of the quadriceps musculature here. Femoral nerves, also with anterior approach to hip replacement, this nerve is in danger. Also the lateral femoral cutaneous nerve, but sometimes also the femoral nerve. So the femoral nerve is here. You can see some scarring around it. And on your T2FETSAT images, you can see the signal hyper intensity of the pseudo fascicles there. And probably in this case, a retractor hook caught the femoral nerve and this patient also had denervation downstream. Now let's move on to the sciatic nerve. So obviously the biggest nerve in the lumbosacral plexus receives contributions from L4 to S3. Gives motor innervation to the hamstrings mostly, co-innervates the adductor magnus with the obturator nerve, as we have seen, and gives sensory innervation really not to the thigh, but to the popliteal fossa and below the knee. So that's a differentiator clinically. Now, how is it built and where does it run? So it's usually built in front of the sacrum. So when you have sacral fractures, it's in danger there as well. But it receives most contributions from L3, L4. It also receives contributions from S1. So this S1 will join, and then it exits the pelvis near the sciatic notch, and then it dives beneath the piriformis muscle, which is this one, and then exits through the infrapiriformis foramen into the subgluteal space. So this is the gluteus maximus, that's the subgluteal space. And there it runs, it descends laterally, and then gives rise to the hamstring motor innervation. Here we have a sciatic neuropathy. And so this now has its own entity or is its own entity. So this is scarring of the subgluteal space. So we have the gluteus maximus here. You can see its atrophy. So this patient got a charley horse in the buttocks region and had a subsequent post-traumatic atrophy of the gluteus maximus. Then you can see the strands of scar here in the subgluteal space, and a highly abnormal sciatic nerve. So based on what Dr. Fayad just showed us, that's probably a grade three injury. You can still see the fascicular pattern, but it's hyper-intense and markedly enlarged. And you can see how these scar strands scar encase that nerve here. So this is what's now called subgluteal syndrome, and sometimes they try with endoscopy to resect those scars. So here's another schwannoma of the sciatic nerve. Again, the target sign with that central hyper-intensity here, hyper-intensity here. And you can usually see this should resemble the T of a golf. So the golf ball and the golf tee here. So that is typically more fascicular than this lesion here, which is a sciatic neurofibroma. So this is more diffused. It's not confined to usually one fascicle and involves the entire nerve. It does not have the target sign. And with contrast, you get this diffused enhancement. So that is useful for differentiation here. So quite a big one. Obviously, then you look for neurofibromatosis and some genetic abnormalities and what's there in the history. This is an unusual case, but an important one. That's an intrasciatic vascular malformation. And the reason for those is we see malformations every now and then, but when somebody wants to embolize them, it is important to know whether there is an intraneural extension. And in this one, you can see the sciatic nerve here deep to the hamstring muscles is enlarged. There's definitely vessels in there. And with contrast, you can see those enhance. If you do dynamic contrast enhancement, you can see that they come with the vessels. And so that's an important finding there. Here's a very similar case to what Dr. Fayyad showed. So after hamstring repair is this case, after hamstring tear and repair, there's also this tethering and encasement of the sciatic nerve here, enlarged signal hyperintense and abnormal. And so that is a good reason to have sciatica in the actual sense. Now, here's another one that is important to look for. It's more common than we probably detected. It's tough to see on the axial, but that's a split sciatic nerve or a partially intraneural course of the sciatic nerve. So here on the right-hand side, where the piriformis muscle is seen obliquely, you see that some fibers run through the muscle, whereas normally they run deep to the piriformis muscle. And here you can usually see on the satchital, a small slip where one of these fibers runs through, and so this can also be a compressive neuropathy. Now last nerve we're going to go through is the pudendal nerve. That receives contributions from the sacral plexus, so the sacral nerves, S2 to S4, by the books. It has motor function to the sphincter muscles and the rectum, and it has perineural sensory innovation, which is around the inframedial buttocks area. So the pertinent anatomic landmarks is the infrapiriformis foramen, so it runs medial to the sciatic nerve, then the ischial spine, and then what's this called? Alcox canal. So this is a canal that's medial to the obturator internus muscle, where it runs in one of those canals. And so, let's review. So it gets contributions from the sacral plexus, so you start with one of the sacral foramen here, and then it runs medial to the formation of the sciatic nerve that we reviewed before, and then it enters through the infrapiriformis foramen, and always runs medial to the sciatic nerve, and then at some point it curves around the ischial spine and turns medial into Alcox canal. That's also where you start seeing the sacrotuberous ligament here. That's one of the lead structures. It's typically always deep to the sacrotuberous ligament, and then it turns into Alcox canal. So that's also where you can easily inject it, and where you can almost cannulate Alcox canal, which we'll probably see later. So here are some neuropathies. So this is one of the rare pudendal neuropathies. So this is a bodybuilder, and as you can see, you cannot see almost no fat. So there's only a little bit of fat here subcutaneously, but this patient basically has no subgluteal space. There's no fat, and the ischial rectal fossa, there's also almost no fat, and you have bright enlarged pudendal nerves bilaterally, which is likely from a muscle hypertrophy compression. Then you also get the pudendal schwannomas. So this one does not show the target sign, but it turned out to be a schwannoma right here at Alcox canal, deep to the sacrotuberous ligament, and then the last case is one that we sometimes see after injury. So sometimes you have perineural scarring off the pudendal nerve, and sometimes it's subtle. Here on the left-hand side, you can always compare is the normal Alcox canal with the pudendal nerve, and here you have the perineural scarring in Alcox canal, which is a good reason to have a compressive pudendal neuropathy. Thank you very much. Good morning, everyone. So nerve entrapment syndromes are commonly encountered in clinical practice. Shown in this slide are the various nerves that can be affected. This talk will focus on the peripheral nerves at the lower extremity. Ultrasound and MRI are the two main imaging modalities, and here is a summary of each technique's advantages and disadvantages. In general, ultrasound is usually sufficient for superficial nerves, and MRI is recommended for deep nerves or nerves surrounded by bone or air-filled structures. The most important advantage of ultrasound is dynamic evaluation, which can detect nerve dislocations and compression. On the other hand, the superior contrast of MRI enables detection of subtle alterations in nerves and muscle, allowing for more precise monitoring and follow-up. I will focus on three features of nerve entrapment, so change in caliber, whether focally or diffusely, change in signal or MRI, or echogenicity on ultrasound, and lastly, change in surrounding or related structures, which is a secondary finding but still helpful, as was mentioned earlier. Example is denervation changes like muscle edema and atrophy. So the imaging findings can be classified into three types, which is based on this old movie that I have never seen, but which is one of my father's favorites, The Good, the Bad, and the Ugly, but we will switch the first and third panels to come up with the ugly, the bad, and the good. So this is the first case, 46-year-old female, sustained a knee dislocation. We see right here the tibial nerve, and here we see the common peroneal nerve coming up in yellow, a little bit brighter than expected. Now we see it disappearing more inferiorly at the level of the injury. And finally, we see it reconstituting further distally just as it courses around the fibular net. So here are key images we can see at this slide showing a completely transected common peroneal nerve, shown here is the distal stump. So common peroneal neuropathy is the most common mononeuropathy in the lower extremity. The nerve is one of two terminal branches of the sciatic nerve and has both sensory and motor functions. Owing to its superficial location around the head and neck of the fibula, it is prone to direct blows or lacerations in this area. And it's especially vulnerable in fractures or dislocations of the fibula. You don't always need a big traumatic event to injure or entrap it. Seemingly innocuous activities like habitually crossing your legs, squatting, or kneeling for extended periods of time, such as carpet layers or farmworkers, also known as strawberry picker's palsy, can also cause symptoms. So grossly abnormal findings of nerve entrapment are usually seen in acute traumatic lesions like frank nerve transection. It leaves you with no doubt that the nerve is abnormal not only because of morphology and signal, but also because of the surrounding or related structures. Although nerves are small because of their location, they have well-established associations with certain abnormalities. Apart from the common peroneal nerve and knee injuries, others are sciatic nerve injury due to posterior hip dislocation or hip fractures, iatrogenic injury of the femoral nerve during intra-abdominal or gynecologic procedures, and obturator nerve damage and pelvic fractures. So this is our next case, 39-year-old female, inability to flex the right knee after jumping. We're going to show here a normal left sciatic nerve for reference. And here we can see on the right side somewhat ill-defined appearance of the right sciatic nerve. We see the culprit, that bare-appearing ischial tuberosity associated with the hematoma, which is likely causing the abnormal findings in the right sciatic nerve in pink. And here we have key images. Again, coronal image, abnormal caliber of the right sciatic nerve and abnormal surrounding structures. Now this is another case, 41-year-old woman, right knee hyperextension injury while kiteboarding, felt a snap and had bruising in the posterior thigh. On MRI, the ischial tuberosity is again bare. That's a complete hamstring avulsion. We see a somewhat unremarkable sciatic nerve adjacent to a retracted stump of the torrent tendon. Unfortunately, the patient had persistent and progressively worsening sciatic neuropathic pain symptoms for the next two years while running or jumping. There was also this large lump in the region that becomes more prominent upon hip extension. An MRI was repeated on T1. We see again bare ischial tuberosity absent proximal hamstring tendons, bringing that sciatic nerve in yellow closer to the bone. We see the gluteus maximus right here. However, at this area where we expect the sciatic nerve to be surrounded normally by the biceps femoris and semitendinosus, this nerve is uncovered and empty, and adjacent to it is hypo-intense lesion medially. That becomes more prominent distally. This represents fibrosis or scar tissue. The sciatic nerve fascicles are also a bit thickened, as we can see here. And finally, at the level of the patient's lump, we see the retracted but atrophic stump of the biceps femoris. So this was the corresponding long-axis image on ultrasound, the sciatic nerve in yellow, retracted stump of the torn biceps femoris in blue. Dynamic examination was performed. And here we can see that during muscle contraction, the two structures are pulling, and this is consistent with cicatricial adhesions tethering both structures. This was also confirmed on dynamic MRI. We see the two structures moving together. So unlike the grossly abnormal findings of nerve transfection, some cases of nerve entrapment can have abnormal signal caliber surrounding structures or a combination of any of these. Most nerve lesions in my practice fit into this category and include masses or any mass-like lesions, adhesions, and fibrosis. And most of these may need additional testing and some detective work, like in the last case, where in dynamic evaluation, it was a key tool in diagnosing the abnormality. Similar to our first set of cases, associations are important to remember. In this case, sciatic nerve symptoms related to hematoma from a hamstring injury. Other examples of mass-like culprits are femoral nerve and retroperitoneal hematoma, proximal tibial nerve and Baker's cyst, posterior tibial nerve, and any tarsal tunnel mass and plantar digital nerve and Morton's neuroma. The next case is a 40-year-old female with 10 months of pain, plantar aspect of the foot. MRI of the ankle is shown going from superior to inferior. Now, we can see that the posterior tibial nerve here is normal in caliber and signal. The surrounding structures are also normal. No hematoma, no muscle or edema or atrophy like in our previous cases, and definitely no absent muscles. On the contrary, there are too many muscles. So we have the flexor digitorum longus, flexor hallucis longus and soleus, but another slip of muscle is present. This is an accessory. Flexor digitorum accessorius longus, which is seen in 2% to 8% based on cadaveric studies. In the lower extremities, the knee and ankle are the most common sites of accessory muscles, and here are other examples. Unfortunately for the radiologist, nerve entrapment can look like a completely normal study. Accessory muscles are iso-intense to normal muscle and are therefore easily missed, making thorough knowledge of compartment anatomy crucial. Overall findings of nerve entrapment may be grossly abnormal, intermediate, wherein you only have one or two abnormal findings, and finally completely normal. However, as we all know in clinical practice, abnormalities do not always fit neatly into a certain classification. And the same goes for nerve entrapment, where you can have exceptions and overlapping features. This is a 63-year-old female with leg weakness. No injury. This is not a nerve transaction, but definitely grossly abnormal common peroneal nerve as well as surrounding muscles. And lastly, a 24-year-old male with symptoms of tarsal tunnel syndrome. Normal posterior tibial nerve, and the accessory structure here was definitely abnormal. This accessory soleus had severe tendinosis, and along with the severely tendinotic achilles produced this sort of double achilles appearance on sagittal T1. A few take-home points. Nerves in the lower extremities or in the periphery have well-known associations with certain abnormalities. For example, common peroneal nerve, knee dislocation, sciatic nerve, hamstring injury, and posterior tibial nerve and accessory muscle. Anatomy and clinical correlation are important for precise evaluation. Compartment anatomy is especially critical in detecting accessory structures. Finally, ultrasound and MRI are complementary rather than competitive techniques. In my experience, especially for complex cases, both are usually necessary. Thank you. My objectives for you at the end of this lecture are to be able to describe the etiologies of cubital tunnel and carpal tunnel syndrome, the two most common nerve entrapments of the upper extremity, as well as the primary and secondary appearances of these syndromes. And you've already heard many of the generalities about this already. Muscle edema, the muscle atrophy, but it doesn't hurt to just repeat it. So there are a lot of nerves in the upper extremity. And again, as you saw, for the lower extremity and the pelvis, there's a lot of nerves that we can look at. For the sake of time and 10 minutes, we're going to concentrate on the ulnar nerve at the elbow and the median nerve at the wrist. Again, the two most common upper extremity entrapments. But if you're interested, this is a review article I co-wrote in 2010 that goes into lots of detail about all the little tiny little nerves and may help you if you're doing nerve imaging. So let's start with ulnar nerve compression at the elbow, the second most common entrapment after carpal tunnel syndrome. And there are four different locations of entrapment. There's the intramuscular septum, which is the arcade of struthers, not to be confused with the ligament of struthers. Ligament of struthers compresses the median nerve, and that's typically associated with an avian spur. This is an intramuscular septum on the medial aspect of the arm. Everyone has it, but sometimes it can get a little bit thickened and can irritate the nerve. But the most common location for ulnar nerve entrapment is at the cubital tunnel. And there are several different causes. One is overuse, so chronic flexion, baseball pitching. If you flex the arm repeatedly, truckers who drive with their arms bent out the window, you actually increase the pressure in the cubital tunnel anywhere from about seven to 20 times normal. Also, by flexing your elbow, what you're doing is you're putting tension on that nerve. Have any of you just been on your cell phones for a long time and realized that your pinky was getting numb? If so, then you realize that that's what you're doing. You're compressing your ulnar nerve. But then there are some other causes as well. Translocation or snapping, compression for an accessory muscle as Dr. Aflores had just mentioned in lower extremity, and constricting bands, which I do want to bring your attention to. So here's a baseball pitcher, a professional pitcher. This is an axial proton density image through the elbow. You can see this enlarged ulnar nerve. It's not just enlarged. We've lost the fascicular appearance, and it is hyper intense compared to a normal age-matched control where you see a normal-looking ulnar nerve. Now, the reason I have neuritis in quotes is because this is not an inflammation of the nerve. We think that it's enlarged, it's edematous, so it must be inflamed. It isn't. This is an ischemic process. When you have compression or chronic tension on the nerve, what it does is cause ischemia. The ischemia causes edema and swelling, and then you have nerve conduction abnormalities. Now, that was MR, but as the previous speaker just mentioned, ultrasound is also wonderful for looking at peripheral nerves, especially if they're superficial. So here is an axial or short axis ultrasound through the cubital tunnel. Here is the medial condyle, and here is this markedly enlarged ulnar nerve, this one measured, I think, about 25 square millimeters. We'll talk about that in a second. But the other thing I want to pay attention to is try and look at these nerves in the long axis as well. One of the nice things about ultrasound that has an advantage over MR is you can actually tweak your transducer to actually get the nerve in a full longitudinal appearance, where often in MR, you don't get that. If you're lucky, it's just serendipitous that you got the whole nerve in one slice. Usually with MR, with sagittals or coronals, you're trying to piece it together, but with ultrasound, you can actually make it in one plane. So here in this extended field of view, you can see proximally the nerve is normal, distally the nerve is normal, and here it is fusiformly enlarged, and you've lost the normal echogenic fibular appearance. So the question becomes, well, how large is too large in the cubital tunnel? And this was a meta-analysis that we did a couple years ago, and we looked at 19 studies. It turns out that about 10 square millimeters, maybe 10.5 square millimeters is a good cutoff for nerve enlargement at the cubital tunnel. You should be aware that this paper was just published. In fact, it's not even out in print yet. This was in the table of contents that I got last week from Skeletal Radiology. So if you look, the publication date is 2026, but it's a beautiful article, and I bring your attention to it by these authors. There are some beautiful diagrams for anatomy, and they do a very nice job of discussing cubital tunnel syndrome. Now, what they said is that at the condyle, it's about 10 square millimeters, and in the cubital tunnel, it should be more than 15 square millimeters. The problem with this is they're only quoting one paper. In our paper, we had included that article from 2010 that they were talking about. So I think if you actually look at more of the literature, 10 is probably a good cutoff. But again, remember, you have to correlate that with the clinical. You can't just say, oh, this patient has cubital tunnel syndrome because their nerve is 11 millimeters. No, if they don't have symptoms, they don't have cubital tunnel syndrome. Okay. So what are some of the other causes of compression at the elbow? Well, you can have an accessory muscle, similar to what Dr. Flores had just shown, and the most common one is going to be the anconious epitrochlearis. So here on this MR image, you have an axial proton density. This is the medial side. Here is the anconious epitrochlearis. It's an accessory muscle present in up to about 20% of people, but not always symptomatic. But what you can see is it's compressing this nerve. And here, just by serendipity on the sagittal proton density, you can see the condyle. You can see the muscle here. Look what it's doing to the nerve. It's compressing the nerve right here. And then proximally, you have the hyperintensity that's been described by the other speakers. Now again, you can see that with ultrasound very nicely as well. So here's a different patient. Here's the condyle. Here's the nerve. And at this level, it's maintained a normal fascicular appearance, but here's this accessory muscle. And when you go longitudinally, you can see the muscle. Here's the condyle, and you go proximally. Here is that marked swelling of the nerve with loss of the normal fascicular architecture. Lastly, for the ulnar nerve, I bring your attention to constricting bands, and Dr. Fayyad had mentioned this with Parsonage-Turner syndrome, and she quoted Daryl Sneeg, who's one of my colleagues in special surgery, and he's described this in Parsonage-Turner syndrome, but we've seen it at the elbow as well. I've seen a bunch of cases of these. And so here you have the ulnar nerve coming down. This is normal, and again, the nice thing about the longitudinal image is you can actually appreciate this undulating course of the nerve, these kind of hourglass constrictions. That is a constricting band. They're fibrotic bands, probably post-inflammatory, but they cause this constriction. And here in short axis, again, not only enlarged and loss of the normal echogenic fibular appearance or fascicular appearance, but you see this kind of lumpy, bumpy appearance as these bands constrict the nerve. Lastly, you can get a functional compression of the nerve or an irritation of the nerve by translocation or snapping. So in this case, it's a dynamic study. You have to have the patient flexing and extending their elbow, and sometimes you have to have them flex it and extend it against resistance to actually make the nerve snap. Sometimes you'll get a patient that says, yeah, it snaps when I do push-ups or bench press. Well, in that case, what you have to do is scan them against resistance, and basically the way I do it is just pushing against their arm. But here, just to orient you, here's the condyle. Here is the ulnar nerve, and this is an extension, but when they flex, the nerve snaps anteriorly. And then as they extend, the nerve is going to snap back into place. Now the other thing about this that you need to recognize is that it's not always just the ulnar nerve that snaps. It can be the triceps that snaps with it. And so in this case, here's the nerve. It snaps. But there's a piece of muscle that just snapped with it, and when they extend, the muscle's going to clunk back in right there. So let me just run that for you again, just to show you. Here's the nerve. It snaps, and then the muscle snaps. Muscle's going to snap back in right there, and then the nerve. It's a double snap. That's also important, because if the surgeon simply goes in and transposes the ulnar nerve, the patient will still have symptoms, and I have several cases of those as well. Okay. Secondary signs. Again, you've heard this before. In the acute phase, it's denervation edema, and that's really the domain of MR. You're not going to see denervation edema on ultrasound. But in this particular case, a fat-suppressed T2 axial, you can see the edema in the flexor carpi ulnaris and the superficial flexor muscle from ulnar nerve entrapment. But what you can see with ultrasound is not only the entrapment, but also the later phases, the muscle atrophy. So here's the ulnar nerve. This is normal-looking muscle. Here's the humerus. And as we come down, look at the quality of the muscles now, and that's all fatty atrophy. All of these muscles are atrophic. So that's the late phase, and you'll see that with ultrasound. All right. Let's finish up in the last two minutes with carpal tunnel syndrome. The most common nerve entrapment of the upper extremity, and as you know, it's compression of the median nerve, and you'll get nerve enlargement. And again, the question becomes, well, how large is too large? So this article from 2005 thought that the sweet spot was about 10 millimeters. Andrea Clauser from Austria wrote a very nice paper in 2009. She found that actually 12 millimeters was a better threshold, but she also did something very interesting. She looked at the difference in caliber of the nerve at the level of the distal forearm, basically the pronator quadratus muscle, and in the proximal carpal tunnel. And she found that regardless of the threshold size of the nerve, if there was more than two millimeters in difference in cross-sectional area between the nerve and the distal forearm and the proximal carpal tunnel, that was almost 100 percent sensitive and specific for carpal tunnel syndrome. So we actually, when we're doing these patients for our clinicians, we always measure in three different spots. We measure in the pronator quadratus level, proximal carpal tunnel, and the distal carpal tunnel, and I'll show you why in a second. So here's an example, though, of what Andrea was showing, and this is one of my cases. Here at the level of the distal forearm, how do I know I'm in the distal forearm? Well, here's radius, here's ulna, here's the pronator quadratus muscle. This is the median nerve, normal fascicular appearance, and it measures about 8.8 square millimeters. In the proximal carpal tunnel, it's now enlarged to 11.8 millimeters, so there is greater than two millimeters difference, and yes, the patient clinically had carpal tunnel syndrome. You can see this, again, very nicely on an MR, so this is a patient axial PD, axial FATSAT-T2. You can see the marked nerve enlargement, the loss of the fascicular architecture, and the marked hyperintensity on the FATSAT-T2. But what I would urge you to do is also look distally, that is, in the distal aspect of the carpal tunnel. We've written two papers with one of our hand surgeons, and what we looked at was the change in caliber, not here at the distal forearm and proximal carpal tunnel, but between the proximal carpal tunnel and the distal carpal tunnel. What we found was that if there's greater than five millimeters of difference between the nerve caliber here and here, they were not going to respond to a perineural carpal tunnel injection, and those patients needed actually to go to surgery for a decompression. So, again, longitudinal imaging can be very nice in this particular case, and we always do this in short axis, but again, I would urge you to look long axis. It just gives you kind of a better appreciation of what's happening. Just to orient you, this is distal radius, this is lunate, this is capitate. Here's the median nerve coming down. Notice this little bit of constriction here in the region of the distal carpal tunnel, and a little bit of swelling here more in the proximal carpal tunnel. This was a case I just did last Friday of a guy who had had a carpal tunnel release a couple years ago and had absolutely no relief of symptoms. Not done at my hospital, but he was seeing one of our surgeons as a second opinion. So, here you can see this marked compression, so again, distal radius, this is the lunate, here's capitate. Look at this marked compression in the distal carpal tunnel, almost complete hourglass constriction, and then the marked swelling proximally, and then if you do a short axis through this area right here, you can see this markedly small nerve that's measured three millimeters, proximally it was about 26 millimeters, so obviously a huge difference, but look how compressed it is. But notice one other thing. Notice how thick that transverse carpal ligament is, and that's one of the other measurements that our hand surgeons ask us to give them. So, a normal transverse carpal ligament will be maybe .4 millimeters. This measured almost two millimeters, markedly thickened, and this is what the previous surgeon at the other hospital had neglected to actually release. So, what I hope I've shown you over the last 10 minutes or so is that you're going to look for the primary signs of nerve entrapment, enlargement, as other speakers have said, and loss of the fascicular architecture. On MR, you're going to look for high signal intensity. On both MR and ultrasound, you're going to look for external compression, and then you'll look for those secondary signs as well, the changes in the innervated muscles, whether that be nerve denervation edema or actual fatty atrophy. Thank you so much for your attention. And now what we're going to do is have our last speaker, because we've seen now four lectures on nerve entrapments and abnormalities, and the question becomes, well, can we actually do anything about them? And Dr. Motamedi from UCLA will hopefully tell us yes. Thank you, Dr. Miller. Good morning. And yes, now that we've learned how to image the nerves and how to look for their abnormalities, let's learn how to inject them. This is the outline of my talk. And so, what is this about? So this is about ultrasound-guided injection of peripheral nerves. You would inject your medication next to the nerve, and it's mostly the goal to diagnose the source of pain. Is it really the nerve? So this is mostly for nerves that are normal-looking on imaging, but the patient do have symptoms, and you want to know if there is any neuropathic pain. These injections are usually done with the anesthetics, corticosteroids, but also with dextrose. Now, we don't do dextrose in my practice. A little bit of a history of dextrose and prolotherapy. In 2008, it was a New Zealand doctor injected some dextrose around the nerves and realized that it does help with pain, and the idea is that it probably has an effect on the pain-producing C-fibers, but it's basically just the same kind of injection, the technique is the same. So again, it's a diagnostic workup for challenging cases. You want to be always sterile and aseptic. Last thing you want to see there is, or introduces any infection. And always remember that the patient may need a ride home, depending on how much weakness they may have after the injection, even with upper extremities, if they're using, you know, they have to steer the wheel and everything. So why would we do an anesthetic injection? Because that will give us the potential diagnostic benefit, and you would know if the patient would benefit from further treatment, such as ablation, surgery, or other treatments as indicated, and it's a very safe, with a very low complication rate. How about corticosteroids? When we would be injecting that, that's when we're looking for some anti-inflammatory and regenerative effects of the medication. It also has a low complication rate, but that's where ultrasound is really helpful, to avoid injecting it in the wrong places, in particular to the adjacent tendons and ligaments, because that can cause iatrogenic tears of those. So let's talk about some common sites. To start with carpal tunnel, Dr. Miller talked about it, and you know what? We don't do much carpal tunnel injections. If they come to us, we do them, they're relatively easy. But in my practice, carpal tunnel injections are done by clinicians, mostly rheumatologists. They do use ultrasound too, but basically what you want to do, if you're injecting them, you want to just bring the needle next to the nerve, deep to the retinaculum, that would be the issue, and that's where you want to inject it. So it's relatively easy, it's easy for the clinicians to do, and again, we don't do that. But remember that it doesn't usually take care of the pain forever. It's usually short-term, in particular, the more severe pain they have, maybe the less effective it is, and they may ultimately need a release of the retinaculum. This patient wasn't a surgical candidate, so we end up injecting them. The next common one in the upper extremity is cubital tunnel, and for that, there's some small studies that have shown that some patients may benefit from that. We do this, again, most of the time for future planning and for surgical planning, if needed, and as shown by Dr. Miller in this article, it's usually done with a patient supplying the arm overhead, elbow fixed, and palm up, that would be the nicest access to the cubital tunnel. Now, you usually want to find the nerve in between the olecranon and the medial humeral epicondyle, and you see the nerve enlarged here, and that is a good place to inject. However, I've noticed that in some very bony, thin patients, if you don't have enough meat there, I would just go just a little bit, just a centimeter distal to it, and where the nerve lies between the two bellies of flexor carpi ulnaris muscle, and we know that the medication also spreads retrograde, so that would be my preferred location if the patient is very thin in particular, that really helps. Some other common sites in the lower extremity, I want to concentrate on these three locations. So for ilioinguinal and iliohypogastric nerve injection, I almost have a clinic. I don't treat the patients, but I get a lot of referrals from the GI doctors, and this is mostly for diagnostic purposes, and sometimes it does help with repeated cortisone injection, and I see most of my patients with status post hernia repair and C-section, but sometimes from appendectomy too, so this is part of the workup to see if the pain may be coming from that, and basically the ilioinguinal, you can see it in between the internal oblique and transverse abdominus muscle, right somewhere five to ten centimeters above the anterior superior iliac spine, and the iliohypogastric actually next to it, but easier is just to find the anterior superior iliac spine and the two nerves lying next to each other at that level, this is the kind of image that you get, you have the internal oblique here, you have the transverse abdominus here, and the two nerves are nicely next to each other, you can target this fascia and inject very easily, so you want the patient's supine, you find the spine, you find the two nerves in that fascia, and you want to have a linear probe that you will have medial, and your approach is going to be from lateral to medial, and you can easily basically inject this septum, this is a case where I injected these two nerves. How about the obturator nerve injection, Dr. Fritz talked about the anatomy here, some anesthesia indications for us, most important is a diagnostic injection to determine if the pain is responsible for lower extremity pain. We get a few patients for entrapment purposes, like baseball pitcher or hockey goalie syndrome. The way I like to inject this obturator nerve is to inject it at two places, so this I realized yesterday may not work that well, so if you want to really inject it proximally, you may want to use a CT to go into the pelvic portion, but where I go is basically you see the anterior branch between the pectineus and adductor brevis, and then lower down, you actually see the posterior branch between the adductor brevis and adductor magnus, so these are the two areas that I inject back-to-back basically. So how do I do this? I have the patient's supine, hip, and slight adduction, and external rotation, a linear probe, it would be more medial again, and I'm going to go from lateral to medial, and again, patient will need a right home most likely. So here's one level injection for the anterior branch, boom, and then you just advance it further down to the other intermuscular fascia and do that. Now, there has been description about doing one injection higher up, even with ultrasound, but in my experience, you need a thin patient to do that. If the patient is not thin, it's easier to go a little more distal and inject the two basically back-to-back. A lot of times with subtle pain and unusual pains, it is really a good way to determine if that's the reason. Lastly, I want to talk about the lateral femoral cutaneous nerve injection. That's the myalgia parasitica. It's quite common, and it's mostly related to sports or maybe weight gain rather than tight belts, and injecting it helps differentiation from lumbar nerve impingement. This is also relatively easily found. It basically, it's a nerve that, not sure why this is not moving, that is basically superficial to the sartorius muscle right there. It's actually deep to the fascia of the subcutaneous tissue and superficial to the nerve. It's easily found. You have the patient supine, but rather maybe a little decubed because it makes it easier as the injection at the end is very shallow. This way you give yourself more room. You find the spine, the anterior superior iliac spine. You move down to the sartorius muscle, and you find the nerve deep to the fascia of the subcutaneous tissue, but superficial to the nerve. Here's the ASIS. You move down, and you find the nerve here deep to the fascia. It's a very easy injection, and the patients are grateful. Finally, I'm not going to go into depth. These are honorable mentions. These are some of the common injections that I do. It's the genicular nerve injection in preparation for ablation to see if it helps. They're really easily found next to the bones. You can find them by the vessel next to them on ultrasound, and it's a very easy injection with long-lasting anesthetic to see if it helps. The other one is sural nerve injection. You can see pain in that area in runners and jumpers. That one lies right next to the achilles tendon, deep to the fascia, also a very easy injection. And finally would be the lateral cutaneous peroneal nerve, about 10 centimeters above the lateral malleolus, and that's when you see the nerve piercing through the fascia right before that. It's a great place to inject it, also quite easy. Now, the whole point about my talk is about know the anatomy, know where the nerves are. The superficial peripheral nerves are easy to inject. It's safe, and it really helps with proper management and patient selection for further treatment. Thank you very much. Thank you.

peripheral nerve pathologies

MRI

ultrasound

anatomy

Sunderland Classification

nerve entrapments

ultrasound-guided injections

carpal tunnel

clinical applications