Ultrasound of the Lower Extremity: Muscle Pathology - HD

Introduction

Thank you.

In this talk, in order to make it a little more unique and use the time that I have, I'm gonna focus on muscle pathology that would commonly affect the lower extremity. I'm gonna briefly talk about the normal ultrasound appearance of muscle, and then I'm gonna talk about processes that involve trauma masses and diffuse processes of the muscle.

Normal Ultrasound Appearance of Muscle

What I teach my trainees and my sonographers is that when they're looking at what they call soft tissue, as we're seeing here in this CNA clip, it's important to try to differentiate the layers of what you're looking at. That way if you do see some sort of pathology, you can try to localize where it is.

We're looking at the posterior calf here in this example. And the skin is the most echogenic thin layer that you see at the top of the screen. The next layer is the subcutaneous fat. This can be variable in its thickness and it kind of has sort of a marbleized look. There's some genic fascial lines there, but they're kind of irregular in their appearance. And then you see this echogenic line here. This is what the fascia looks like. And this is what's separating the subcutaneous tissue from your first muscle group.

The next muscle here is the gastroc anemia muscle. And you can see how the muscle fibers kind of travel together. They could be oblique or transverse or longitudinal depending on how you have your probe oriented. And then again, when you go to the next muscle group, which is deeper, and here the soleus muscle, you're gonna see that thick echogenic fascial plane again, separating these muscles. You can see again that the fibers are kind of in a different orientation, so that lets you know that you're looking at a different muscle. And if you have any question at all, one thing you can do is just flex the joint that's below the area you're looking, and you should be able to see the muscle during dynamic imaging.

Muscular Trauma

First I'm gonna talk about muscular trauma. There are three major mechanisms how trauma occurs to muscle stretch, direct impact, or penetrating trauma. And the manifestations can include hematomas, muscular tears, fascial injury, and or muscle herniation.

Intramuscular Hematomas

First I wanna speak about intramuscular hematomas. These are very common. They're much more common than other pathologies, such as a mass that would lead to bleeding or a hematoma. For the most part, we can see these know what they are, recommend clinical follow up, and we don't have to worry about them in the long term.

These are usually from trauma, but they can be from spontaneous causes, particularly in the setting of anticoagulation. And what may be happening is that there's a small amount of trauma, it just wasn't recognized in the history. But when you have a patient on anticoagulation, the amount of hematoma relative to the trauma that was present may be out of proportion. So you may see a larger hematoma than you would otherwise expect. Follow up for hematomas in the muscle are not standardized, but they should resolve over a period of weeks. And if there's anything kind of funny about the hematoma, so it's much larger than you expect, but there's not anticoagulation or it's persistent, expanding or otherwise atypical, you do wanna consider some sort of follow up or possibly an MRI.

I'll just show you a few cases of intramuscular hematomas on ultrasound. This was a small hematoma we see on ultrasound and because the history was kind of uncertain, they got an MRI confirmed the findings. So you can see the classic appearance of blood prod on MRI and there was some peripheral but no central enhancement.

This was a gentleman who had a pretty classic trauma history. He was swinging a golf club and hurt a pop and then had pain in his thigh. Here we see a pretty large fluid collection that's between the vast laterals and the vast intermediate. So it is intermuscular. And this gentleman was on aspirin, Plavix, so he probably had a small muscle tear. Sometimes it's hard to see the actual muscle fibers, which I'll talk about in my later slides. But he had a sizable hematoma and this was likely larger than it normally would've been because of his underlying anticoagulation. He was just clinically followed to resolution.

This was a hematoma that was incidentally seen in a patient for a DVT study. And you can see this is a hematoma that's probably subacute, looking at its appearance. So it's got layering of the different parts of the fluid as the elements are settling out. And again, you can see sometimes the muscle gets really kind of stretched out. So you have to look for your landmarks, make sure you use a large enough field of view to see where you are and to see the extent of the pathology that you're trying to assess for. But here you can see that there's muscle on each side. So this is an intramuscular hematoma.

In my practice we have a lot of hemophilia patients that we take care of. So a benefit of that is that we get a lot of follow up for these patients. So this was a patient that had a hematoma between the muscles, predominantly the gastroc anus and the soleus and the calf. And you can see what it looks like at five days. Pretty koic. And then it's a little smaller, a little bit more heterogeneous at two weeks, and then more contracted and heterogeneous at six weeks. So this is the evolution of what a hematoma should do. It should get smaller with time.

And lastly, just another example of a chronic hematoma that's got a kind of retracted and more hyper coic appearance.

Specific Types of Injuries: Stretch Type Injuries

Moving on to specific types of injuries that can occur. And we see this really commonly in the lower extremity, which is why I wanted to focus on it. A stretch type injury commonly occurs in the gastroc anemia, soli soleus, plantars complex. This would be where the soleus muscle is located. The plantar muscle is high and is mostly tendon running down to join the Achilles. And then the gastroc muscle is the most superficial muscle, and it joins the achilles tendon much higher up. Because the gastroc anemia has got sort of fast twitch skeletal muscle fibers, it's used for quick action and it also crosses two joints. It's prone to injury more than some of the other muscles in this group.

When we see pathology in the calf, the classic name is tennis legs. Someone comes in doing some sort of activity and has acute pain or has a popping sensation in the calf. Most of the time this is gonna be a partial tear in the gastroc anemia's, usually the medial head. You can also get damage to the API neurosis of either the gastroc anemia or the soleus muscle. And lastly, you can get plantars tendon rupture, but that's actually much less common, which is why I have it small down here. And the majority of the time you're gonna be looking at injury of the gastroc anemia muscle.

This is the classic appearance. So what you're seeing here is sort of mostly hematoma. And you get this sort of disorganized appearance loss of the normal fibular pattern that you expect to see in the rest of the muscle. If you scan carefully, you can sometimes see the free end of the fibers that are torn here, but the history is gonna fit this presentation. And also you're gonna be able to see that the entire muscle is not involved. So this is not a complete rupture of the muscle, it's just involving one small area.

If we compare this side to the normal side, we can see how we don't see that focal area of disorganization and hematoma. I think this kind of looks like a knot in a tree. And this appearance you'll see repeatedly with partial tears of the gastroc anus.

These injuries also like to happen at the area of the myo tendonous junction. As I mentioned the gastroc anus joins the Achilles and forms its myo tendonous junction, much higher up than the soleus muscle. So you wanna look at this area, and this may be the area where the patient has pain, but these muscle fibers as they attach here could be injured and torn. And here we can see the normal side compared to the abnormal side. And there's some fluid here where we've lost a few of those fibers.

You can also get an a neurosis injury. And if you look at this cynic clip, you can see that the echogenic fascial plane between the two muscles, the gastroc anemia and sous is interrupted here. And this explains how we have hematoma that's then kind of tracking between the two muscles. Otherwise, if you just had tears within the muscle, it shouldn't be able to kind of track in the intermuscular plane. But anytime you see this, it's probably 'cause the aosis has been involved.

And this is just another example of an a neurosis injury here it looks like the gastro anemia and sous have just been kind of peeled apart from each other.

So another pattern that can occur. Plant terrace tear is actually pretty uncommon. Management for these are pretty similar. If you have a partial gastroc anemia tear or plant terrace tear, you're gonna do conservative management, but it's considered to be a slightly less serious injury. So there may be some utility in trying to tell the difference, but what happens a lot of times you see hematoma even tracking between the muscle planes and are unable to see the plant terrace tendon. And it's assumed that the plant terrace is torn whereas most of the time it's really just that it's a gastroc anemia tear or AP neurosis tear. If you're able to see the actual plantar tendon like we had in this case, it was actually disrupted, you could see the two ends, then you can confidently say that it's a plantar tendon tear. But from a clinical standpoint, it's not very important.

There's some other pathology you can see in the cap that can mimic these types of injuries that is important to be aware of. Here we see a fluid collection that looks very similar to the one that was showing you with the gastroc anemia tear and a neurosis injury. The difference here though is the location of this fluid collection. So notice how this is not between the gastroc anemia and the sous. This is between the subcutaneous tissues and the gastroc anemia. So it's more superficial, more posterior in its location than where we were seeing the hematoma with the gastroc anemia tear. And this is more likely to be related to a popliteal cyst that's ruptured and tracking down the calf. This is where this fluid is going to occur. So when you see this, you want to just scan more superiorly and see if you have a popliteal fluid collection. And if it connects, it's much less common for bleeding from a gastroc anemia's tear to go into that tissue plane. So the differential in part of the fluid collection seen in the calf and acute pain in the calf is a ruptured popliteal cyst.

Here's another example. This is quite a large hematoma. Again, it's in that space between the gastroc anemia and the subcutaneous fat posteriorly. And if you look at the CNA clip, you see the classic little, the CS shaped area and the popliteal fossa where we have the cyst. And this is contiguous with this heterogeneous fluid collection.

Another really important thing to remember is that when patients come with acute calf pain, they may actually have a DVT or that's part of the differential diagnosis. I see gastroc tears on my DVT cases and vice versa. Think about that, particularly if you don't see any other muscle pathology. This was a patient who happened to have a thrombus in a gastroc anus vein. So remember that any veins deep to the muscular fascia are going to be deep veins and are gonna need treatment. And so this just happened to be within the gastroc anus muscle itself.

Direct or Blunt Trauma

Moving on to lec direct or blunt trauma, I've had a couple of really interesting cases where ultrasound was useful in just kind of aiding the diagnosis. And this was a gentleman who had a bike accident and had direct impact of his thigh to a stop sign post. So his radiograph was pretty unremarkable, but he had a lot of pain and a lot of swelling in his anterior thigh. And with ultrasound, we could very easily tell that he had extensive lacerations in the compartments in his anterior thigh. So the vastus intermediates and laters particularly, and you can see fluid here, but on this dynamic image where we're putting some compression, it's not only just fluid, you can see that these muscle fibers are definitely disrupted from laceration.

And here's a nice longitudinal view just showing where the normal muscle is located. And then you can see this disorganized appearance where we have hematoma and laceration. And then just one last silly clip. You can see that it's not going through the entire muscle, but this is a high grade tear slash laceration of the s lateralis. This patient didn't need any additional imaging, so they just managed him conservatively, but we wouldn't see that. We didn't see that on the x-ray. We could have seen it on CT or MRI, but we felt confident about the diagnosis from the ultrasound.

Muscle Herniation

This is something that you may see and maybe not in the acute setting, but you may see it as a palpable mass. And this is a small herniation of the anterior tibialis muscle through the fascial layer. So this can caused by trauma from a stretch type injury, the fascia's really tight on the anterior tibialis. And again, it might not be any pain, it might not have been something that was initially noticed, but if you have somebody come in with this palpable mass, particularly positional, it can be felt better in the standing position. You can see that just as the normal appearance of muscle is just kind of breaking through the outer a neurosis and then going into the subcutaneous fat.

Penetrating Trauma

And lastly, for penetrating trauma, you would see similar findings in the other types of trauma. But in addition, because of the break of the skin and the subcutaneous tissues, think about the possibility of gas foreign bodies that you may see. You might see hematoma and fiber disruption and then look for active hemorrhage on your color doppler evaluations.

Masses in Muscle

Next I wanna talk about masses that you can see in the muscle. Primary masses in the muscle, particularly benign ones are really not that common. There's one oma I want to speak about. And then really for primary malignancies of skeletal muscle, that would involve sarcomas. We can see a lot of other types of masses, either benign or malignant that come from other tissue types that are within the muscle. So they are gonna appear intramuscularly, and I'll show you some examples of that. Also, masses in the muscle may actually be originating or emanating from bone or cartilage. Deeper structure. So again, it's important to try to assess the whole area that you're scanning. You can get local recurrence of malignancies in patients that have already had surgery metastases and then mimics or pseudo tumors.

Unfortunately with ultrasound we're not able to always be definitive when we see masses. But there are worrisome features you can think about. Anything that's increasing in size, heterogeneous has a lot of vascularity, and is hypo coic tends to be more on the worrisome side for malignancy. And I just think it's important with ultrasounds, especially if the patients presenting to you for ultrasound for their first image to try to get as much information as you can. So ultrasound may be really useful and may be the only way to prove that there's color flow in a lesion and it's useful to just determine the location of where the mass is. And it's really great for biopsy guidance.

This is one of my favorite cases that started off with the MRI for another reason. Hip pain, and we saw this very round T two bright mass in the upper thigh. They went on to pet CT as the next imaging modality and there was no activity in this mass. So there was uncertainty about whether this could be a hematoma or some other type of tumor that wasn't avid. So they did, they then went to ultrasound, and here you can see this very round, but heterogeneous mass. And with careful interrogation, we were able to show that there was flow within this mass. So we've got an arterial signal here, and also if you notice, there's a lot of mass effect on the adjacent muscle, more than maybe you would expect for fluid collection. So this turned out to be a low grade mix. And these tumors are a really major mimic for hematomas. I've seen more than one of these now, and you have to really be careful to use low power settings and low flow settings to look for color doppler. But we were the modality that first was able to show that this was a mass and we subsequently biopsied it and then they had it removed.

Other masses you can see in muscles. So this is an intramuscular hematoma. So these can have a variety of appearances, but usually more echogenic. And this was confirmed with MRI.

This was a patient who had had a prior vascular malformation and you can see that there's this hypo coic mass with some colored doppler flow. And again, to prove this, we got an MRI, this was very bright on T two.

This was a patient with a history of neurofibromatosis and you can see that there's this oblong very well marginated mass with very little color doppler flow present. And if you correlate this with the MRI, it was T two bright with enhancement and given the history and given that multiplicity of masses as this patient had in other locations, this was confirmed by imaging alone to be a neurofibroma.

This was a recent case I had in my institution. And as you can see, this is a very large heterogeneous mass with color doppler flow. So the one thing that's nice about imaging primary muscle malignancies or sarcomas is they're usually not subtle at their primary presentation. So looking at this, you would be extremely suspicious for malignancy. And when we use our high field imaging or high frequency transducer, it's just nice to be able to see that this is actually within the muscle. So you can see the subcutaneous tissue and then you see the muscle layer and the mass is within it. And then we did an MR, I showed this large heterogeneous mass with enhancement and this was a lipo sarcoma.

It's important to remember that sarcomas when they occur, they tend to go along the surgical plane or surgical margin. This was a patient who'd had multiple prior surgeries for sarcoma and he was in our department for a DVT study and one of my sonographers incidentally found this mass. It's a pretty homogeneous mass. It does have color doppler flow. We also got an MRI just to look at its appearance, but this was right where he had had his prior surgery. And this was a recurrent myo myo fibers sarcoma that we also subsequently BioE with ultrasound. So local recurrence of sarcomas is common.

Here's another example. Again, not subtle, you'd be able to see this nicely with ultrasound. Just remember that history is important and in someone who's had a prior surgery for sarcoma, you would be very suspicious of this mass and they can be less subtle. So this is a small nodule, it's hypo coic, but it's deep, it's within the muscle. This isn't an area you would expect a lymph node to occur. So with this history, even this tiny area is suspicious, you can get muscle metastases. So melanoma is a malignancy that likes to go anywhere, particularly in the muscles. It has a very hypo coic and vascular appearance. Here you can see it's just deep to the muscular fascia, kind of splaying apart the muscle fibers. And then this is showing it on the pet CT with the very strong avidity.

Again, just wanna emphasize the importance of looking at the characteristics of what you're seeing on your ultrasound to just try to get more information. So in this case, we're looking at two images where this area is predominantly fluid. You may think, is this an abscess, is this a hematoma? Or some other process. But if you look very carefully where I have the arrows, there's this thin curve, linear areas of echogenicity. These are consistent with calcifications. And if you look at this non-contrast ct, you can see the same calcifications. So this is taking up the thigh musculature, but this was in a patient who'd had a history of a chondro sarcoma. So that was a recurrence and that explains the calcifications. So this wasn't something that primarily came from the muscle, but was involving it. And this just gave us a clue about the type of tissue we were looking at.

Similarly important to look at the whole field of view when you see a mass. This was a large mass definitely in involving the space of the muscles in the thigh. But if you look at the deepest part of the image that I'm showing you, you can see the cortex of the bone is disrupted and this mass is actually emanating from it. And this is shown really nicely on the MRI as well post contrast. So this was a large osseous metastasis from lung cancer that was originating in the bone and then involving the musculature secondarily.

This was another case. I had this young female who had this large mass in her thigh. She also had diffuse enlargement of her thyroid gland, and we did a biopsy of this mass under ultrasound. And notice here how you can see that the musculature is actually pushed very far anterior. So it's thin and this mass is appearing somewhat separate. And on the cynic clip, the important finding here is that you can see that there's irregularity along this cortex of the femur. So that kind of shaggy line is very abnormal. And what was happening in this case is there was a break in the femur posterior on our legs. So an area we weren't imaging, but all of this mass was emanating from the medullary cavity of the bone. And it was just pushing the muscle anteriorly. And this was a lymphoma of osseous origin.

Mass Mimics

Lastly I wanna talk about a couple of mass mimics. So if you see a focal mass in the muscle with a lot of calcification, and if you're lucky to have an x-ray to correlate it where you can see the calcification, this may be myos myositis ants. So to ensure this, you wanna think about the patient history and then potentially do a follow-up. But you don't wanna mistake this for a malignancy.

Again, scar tissue can look very odd on ultrasound. This was in the gluteal region. We see this very heterogeneous mass, a lot of shadowing, so hard to actually see the characteristics of the mass. And this was biopsied because it wasn't certain what it was and because of its size and this just turned out to be a rigorous amount of scar tissue.

Diffuse or Infiltrative Processes

Lastly, I wanna talk about diffuse or infiltrative processes you can see in the muscle. So first you can see atrophy. And so if you just compare one side to the other, in this case, this was looking at the calf muscles. One is larger than the other. The muscles should look pretty normal in its configuration or morphology. Otherwise it can be increase in echogenicity. And this can be a unilateral process if it's something that is from disuse or other kind of trauma or even innervation or you can see it more diffusely from systemic diseases or medications such as steroids.

Another condition that we don't see commonly, but it's good to be aware of, is transient muscular edema. After overuse of a muscle, you can have delayed, it's called muscle soreness. So it usually peaks several days after activity. And if you look with ultrasound, you just see diffuse increased genicity of the muscle. And you would also see that on T two MRI. And this is a self-limited process that's just gonna go away in a short period of time. So if there's any uncertainty, that's the way to ensure that you've made the right diagnosis.

Infectious myositis doesn't usually occur in otherwise healthy persons, and it may require more intense therapy than cellulitis alone. So they may need to have surgical debridement, they may need to have IV antibiotics instead of just oral antibiotics. So it's important to recognize when your soft tissue infections have extended deep to involve the muscles. Also you wanna think about concurrent osteomyelitis or joint infections, and you may or may not be able to see that with your ultrasound, but think about looking for bone irregularity or joint effusions, and there can be a variety of appearances of myositis and the history is also important.

This was a young female with procoscious puberty who had a Lupron injection into the muscle. So you can see here this looks really mass like this hypo coic area with a lot of vascularity. This was homogeneously enhancing on the MRI, but with the history of having the injection there and her clinical findings, this was consistent with focal myositis. She was treated in this resolved over time.

Again, this case is pretty clear that there's this fluid collection that's got some debris and layering, and this is definitely within the thigh muscle. So we've got the subcutaneous tissue, then we see our muscle fibers, and then here we see this abscess. This is the MRI correlate. So you can see the same abscess ca cavities here where there's no enhancement. But notice how extensive this is in the muscle, which we really didn't appreciate as much on the ultrasound. There's just in intense enhancement throughout the muscle. So it's important to recognize this on ultrasound because again, this is a really advanced infection and this patient may need more aggressive therapy.

Just another example of an abscess, how it can look kind of mass like especially early on, we see just a hypo coke area with vascularity. And then if you look at the CT scan, clearly we have this thick rim of enhancement with some more central fluid component.

Moving on to a different process. This was an older gentleman who came into the hospital for other reasons and had very acute onset of pain and swelling in his calf on the right side. And I love showing this case to my sonographers because they almost always think right away that it's a fluid collection. But if you look carefully at this cine clip, you can see that we've got all of this echogenic architecture within this. And this is actually just the gastroc anus muscle. So it's not a fluid collection, it's the muscle that's just markedly expanded in hypoechoic. So if we compare this to the other side, this was the medial belly of the gastric anus. This muscle is enlarged in hypoechoic and this was most consistent with muscle infarction given his history.

And last case I wanna show you is in a patient who had a known history of lymphoma. He had a CT scan that showed some increased density and some extra kind of soft tissue in the posterior gluteal region. So this was actually the piriformis muscle. They were worried about potentially hematoma in this location. But they got an ultrasound and you can see that this is a very hypo coic appearance of the whole piriformis with a lot of color vascular flow. So this was not a hematoma, this was diffuse involvement of the piriformis with lymphoma. And then we were able to do a biopsy to confirm that. Much easier to tell the difference using ultrasound in this case.

Conclusion

In conclusion, muscle pathology is common in the lower extremity and in other muscles, and I think it's something that's not always talked about or easy to get answers regarding. It can be most commonly trauma, lots of different types of masses or also infiltrative diffuse processes. It's helpful to be aware of pseudo tumors and other mimics. So if you know classic appearances of some of the pathology such as trauma or some of the benign masses, it'll help you to kind of form your differential diagnosis. Be really careful with the Doppler evaluation, especially for those low flow tumors that I showed that can look like fluid collections. And if there's any uncertainty, we can't always get the exact answer with ultrasound. Have a low threshold for follow-up or other imaging if you're unsure.

Thank you very much.