 Hello, my name is Jim Wu. I am the chief of mesosolder radiology at Bethesel Deakins Medical Center in Boston, Massachusetts. I have no disclosures. Our learning objectives are to first learn the definition of a bone tumor mimicker, learn the various categories of bone tumor mimickers, and then learn the key imaging and clinical features of these bone tumor mimickers in order to prevent inappropriate treatment. Miriam Webster Dictionary defines a mimicker as someone to be an imitation of, simulate, or closely resemble. So essentially a bone tumor mimicker is any lesion and bone that looks like a bone tumor. And so this includes a lot of different lesions. Many lesions and bones are not true neoplasms, and it's important to know the common mimickers in order to prevent misdiagnosis and inappropriate treatment. And also we don't wanna subject a patient to unnecessary tests and anxiety for them to think that they actually have a bone tumor when they do not. Bone tumor mimickers can be classified within these different categories. Normal variants can general developmental processes, traumatic disorders, metabolic and arthritic, infection, nitrogenic, and technical artifacts. And we're gonna go through these categories so that you can see the variety of lesions that can mimic bone tumors. All right, normal variants. So these are all lesions that can be normal, but they can look funny on imaging and make us think that there's a bone tumor when there really isn't. All right, so here's a lesion here in the distal femur, and this looks really suspicious. It's very well circumscribed, and it's pretty bright on the T2 fat sat image. But the main thing is you wanna compare this to skeletal muscle whenever you see a lesion and bone. And we can see that this is brighter than the skeletal muscle, so it has to contain fat. And essentially things that contain fat in bone are pretty much all benign. There's very rare things that would contain fat that could be malignant. And so this lesion's hyper intense skeletal muscle on T1. As opposed to this lesion, if you look at this lesion, we can see that the process in the bone actually comes outside of the bone. It's a big soft tissue component, and this signal intensity is darker than the skeletal muscle. And on the T2-weight images, it is very hyper intense, and there's a big skeletal component coming through the bone here. So the key point is red marrow should not be hyper intense to normal skeletal muscle on T1-weight images. And in this case, this was a case of lymphoma. So red marrow transitions from red to yellow with increasing age, but you can still have little bits of red marrow that remain in the metaphysis along bones. The key feature is that red marrow should be hyper intense or brighter than skeletal muscle on T1-weight images. Another feature is that red marrow should not extend into the epiphysis. It should stop at the fysil scar. So here's an example. We can see in the knee this hype intensity signal here, but it forms a very sharp line right at the fysil scar. And so red marrow should end right at the fysil scar, should not extend into the epiphysis. As opposed to this case, where we can see that first there's abnormal signal within the proximal tibia, and this is just as dark as skeletal muscle. So already we wanna be worried about this process. It's very bright on the T2-weight images, and then this process crossed into the fysil scar. And so this is very concerning. And this turned out to be a case of B cell lymphoma. Besides red marrow, there's a couple of other things that can be normal that can look like a lesion. And we just don't wanna confuse these with true bone tumor. One is Ward's Triangle. So this is a triangle area of lucency within the femoral neck. And you can see that this is outlined by the compressive and tensile trabecular lines of the femur. And it's less apparent in osteoporotic patients due to the loss of trabecular lines. This is a normal finding. Another normal finding is this humeral pseudocyst. If you look at this radiograph, it looks like there's a lesion right here within the lateral aspect of the humeral head. And this can look very suspicious. So this is due to a normal decrease in trabecular lines, and there's usually a little bit more fat in the rest of the humeral head in this area. And it's best seen actually on the external rotation views. If you're concerned, you could always go and get an MRI. In this case, you can see that in that same patient, there's just normal fat in that area which accounts for that lucency. Another area which is similar to that pseudocyst in the humeral head is the pseudocyst in the anterior calcaneus. So this is a lucency within the anterior calcaneal body where you also have opacity of trabecular lines within this area. You don't want to confuse this with the introsys lipoma, which is actually a true neoplasm. And sometimes it can be hard to tell. However, the introsys lipoma usually will have this strophic calcification from fat necrosis within the center of the lesion. Moving on to congenital and developmental abnormalities, these include the synovial herniation pit or the otherwise known as pit's pit, the supracondral process of the humerus, the sodial line of the tibia. The pit's pit is a lesion within the superior lino aspect of the femoral head and net junction. This is first described by Dr. Michael Pitt in 1982. And it's a rounded lucency and it should have a thin sclerotic rim. So it should be in this exact location, a lucent lesion and should have a thin sclerotic rim. It doesn't have those three features that we don't want to call the synovial herniation pit. It's believed to do the normal variation of the hip capsule against the femoral neck and it has an associated femoral saturer impingement, but you don't want to over call this as such as a metastasis or an additional lesion there. Here's a pit's pit on CT. We can see again, it's in the classic location in the anterior aspect of the femoral neck has a lucent center and a thin sclerotic rim. Another lesion that could be confused for a tumor is the super conical process of the humerus. So this is a bony spur that arises from the anterior medial aspect of the humerus. It's a C in about one to 3% of the population and it's a congenital variant. And you can mistake this for a osteosarcoma or a osteocondroma arising from the humerus. One key feature is that you can have something called the ligament of struthers that arises from this lesion and then attaches on to the medial aspect of the humerus and it forms a tunnel which compresses the brachial artery in the medial nerve. And so here's the super conular process and here is a diagram where you can see this and then the ligament of struthers arises from this and attaches to the medial aspect of the humal picondyle. And then in this tunnel, the brachial artery and medial nerve can get compressed. So the align, this is something that we see all the time and it can be mistaken for a stress fracture or osteodosteoma or some tug lesion. And in this case, this is a tug lesion at the attachment of the soleus muscle. So the sole muscles will attach onto the back part of the tibia and back part of the fibula. And this line always goes in the upper one-third of tibia and goes lateral to medial as you go down towards the ankles. It's gonna go in this direction and this can look very aggressive. On CT, we're gonna see this little calcification here. Here's a different case. You can see a little tug lesion back here and this can mimic periostitis from a tumor, a trauma or infection. And you can see similar changes on the fibular attachment of the soleus muscle as well. You just don't wanna over call this as some type of aggressive lesion attacking the tibia. So here's example of a soleal align back here. Here's an example of a stress fracture. And here's an example of an osteoid osteoma in the same exact location. And there's the leucinitis. Traumatic disorders can mimic certain tumors including the subarperiostal hematoma or stress fracture. So this is a lesion on the back part of the femur that we see here. On the MRI, the T1 weighted sequence, we can see that it actually is fatty or bone marrow type process within this. And so what is a subpareostal hematoma? It's a surface lesion caused by bleeding or lifting up with a periosteum and then this area will actually ossify and form a mass. Remember that your periosteum is highly vascular and it's very closely adherent to bone. So when there's trauma and it lifts off, it can cause this collection of blood that fills up in this area and eventually can lead to ossification in some cases. The next traumatic lesion would be a stress fracture. And if you see something like this, you're probably not gonna over call this as a tumor, but sometimes these can look very, very aggressive. Remember that insufficiency fractures occur when you have normal stress applied to weak bones and fatigue fractures are where you have excessive repetitive force that's applied to normal bones and both of these are subsets of stress fracture. Here on the MRI, we can actually see that there's edema within the second and the therminotarsal, but there's a lot of soft tissue enhancement. In this case, it's helpful to see that there's two lesion because the chances that you have two bone tumors right next to each other would be very unlikely, but then we can, so the stress fracture would be more likely in this case. This case can be pretty concerning. In this case, we can see here on the T1 wave image, we see this area of marrow replacement within the left sacral ala. And again, remember, we wanna compare this to skeletal muscle. And in this case, it looks as dark as skeletal muscle, so it looks like there's something replacing the marrow in this area. But this is really just a case of a sacral ala fracture. We were worried about this, wasn't sure what it was. Repeated in the MRI six months later, that area looks completely normal, so it resolved. Moving on to metabolic arthritic processes. We're gonna talk about brown tumors seen in hyperparathyroidism, malaristosis, austenicosis, patches disease, and calcific tenonitis, and as well as subchondral cysts. So brown tumors, you get these in hyperparathyroidism, and these can look really aggressive. I mean, this could look just like a renal cell metastases or a lung cancer metastases. The good thing about it, this is, if you treat the parathyroid anoma, have that removed, usually these will go away or these will improve, and the person had, in this case, had the parathyroid anoma removed, and we can see that there's increased sclerosis and healing of the lesion after six months. Malaristosis, this is a benign bone dysplasia, and you can get these sclerotic bone lesions on the surface of the bone, and it usually involves a sclerotomal distribution, and they'll describe this as sort of a dripping candle wax appearance along the bone, sort of like this here. And 50% will show signs of these by age 20, and most of these patients are actually asymptomatic, but sometimes people can have limb pain, they can have muscle or tendon shortening, they can also have other things like skin disorders and poor circulation. Osteonecrosis, this is ischemic necrosis or decreased vascular supply to the bone and bone marrow leading to these bone infarcts, and this is seen in a bunch of disorders, but the two most important ones are probably trauma and steroid use. So remember that bone infarcts occur in the metaphysis or diaphysis and do not contact the articular surface, whereas ABN touches the joint space and touches the subconscious bone, and ABN is more problematic because that can lead to a collapse of the bone here, and they typically get this double line sign on the T2 weighted signal. On the radiographs, you can see this well circumscribed area here with sort of this peripheral zone of calcification and internal density here. On MRI, this is sort of the classic double line sign where you have a double line of low T1 and high T2 on a T2 weighted image. Padgett's disease can look different depending on the phase. On this side, we have one of a chronic phase where you see the bone and with medullary and cortical expansion. This is the lytic phase of patches which usually begins at one end of the bone and works towards the other, sort of the blade of glass or the flame shape appearance of Padgett's disease. That's the chronic phase and this is the lytic or acute phase. So Padgett's disease, it's abnormal bone remodeling which leads to the osteoarthritis expansion and this deformity. Rare in the young and also rare in Chinese and it's linked to the paramixal virus but the cause is still not fully understood. Remember the active phase looks very different. You get that blade of grass or flame pattern and one exception is the tibia in which the lucency can begin at the center and then work towards the ends of the bone. The pelvis is definitely gonna be the most common site involved and it's often unilateral. Right, calcific tendonitis. So this is hydroxyapatite deposition in and around the tendons and it's most common in the rotator cuff and the hip, however it can appear in any tendon and usually the time that you get in trouble is the acute flare or you get erosions in the bone and calcifications and one of the key features is just to know where your tendons attach. Just if you see some bone lesion, bone destruction of the bone, say, hey, could this actually be where one of the tendons attach and to see if this is a case of calcific tendonitis? For instance, here in the femur, we're gonna see that there's some calcium for right where the gluteal muscles attach and we see some bone erosion. We don't wanna over call this as the surface lesion of the bone in this case here. So this is a case of calcific tendonitis where the gluteal muscle attaches. This is a case of a breast cancer metastasis but in this case, this is on the medial side and this is not near where any tendon attachment occurs. And then here's the plane film showing the lidic lesion for the breast cancer metastasis. Right, so these lesions that we see all the time, however, this is probably one of the largest ones of these lesions that we see and we can see that this is pretty, it has sort of fluid signal on both the T1 and the T2 weighted sequences and there's also really bad osteoarthritis, the glenochemal joint and this lesion goes right up to the subcontral surface. On the radiograph, it's actually kind of hard to see. You can see the really bad osteoarthritis, there's bone on bone but we don't really see the lucent area or the lidic lesion very well. So this is actually a case of a subcontral cyst, very, very common due to osteoarthritis. Essentially, once the cartilage gets destroyed, you have fluid that goes through the little crevices within the bone and it can form these large cysts due to increased joint pressure. It should always abut the joint surface. If I see a subcontral cyst, I wanna look very, very carefully for a connection of the subcontral cyst on the line bone. Brody's abscess, this is something that could definitely mimic a lesion. Here we can see that there is this chronic infection where you can see the sclerosis within the ulna and a small lucency from the central nitus of the infection. It can get confused with other things including osteoid osteoma. Here we see another person with thickening here of the proximal tibia and we see the lucent center here. This was a case of osteoid osteoma but these can look very, very similar in these instances. Another case of the Brody's abscess here, we can see that there's irregularity here in the femur and here on the T2 or edema sensitive sequences, we can see the collection of the abscess within the distal femur with a lot of surrounding edema. Iatrogenic causes, so there's a bunch of things that we do to the patient that can lead to findings in bone that look very suspicious for bone tumors. One of the things is biceptinidesis and this is one of my biggest pet peeves because we see this all the time and oftentimes the resident of the fellow or the radiologist never looked at the clinical history and never figured out that the person had surgery here and so this comes to us that there's an aggressive lesion in the humerus and they want a biopsy for this thing but if they just look at the clinical history or if we talk to the patient, they would realize that this is at the site where the biceps has been reattached to the humerus, right? Another thing is bone marrow biopsies. We see, we do these all the time. We don't usually image these all the time but you want to be aware of this. In this case that we see that there's a lesion here within the left iliac bone, high signal here on the T2, low signal here on the T1 and this was somebody who had a recent bone marrow aspiration and again, look at the clinical history, make sure that you can try to figure out if could this be a real lesion or is this something that we did to the patient? In this case, this is related to the hardware. We can see that there's these big, loosent lesions surrounding not just the femoral component but also the acetabular component and the other thing is that the loosent disease actually do not confine to the outline of the bone and so this is actually a case of particle disease. It's a common cause of hardware failure and basically you can have a response to the cement, to the polyethylene, to the metal, to anything related to the prosthesis and you get these loosent ceases around the hardware and one of the key features is that these lytic areas do not confine to an outline of the prosthesis that they're much more irregular. If you see that confining to the outline of the prosthesis it's more likely to be due to mechanical loosening. Radiation changes. In this case we can see that this was a lady with breast cancer and we can see the margin of where the field of radiation occurred and so up here was where they did the radiation and now the bone marrow is all fatty replaced. Early on when there's radiation this causes vascular congestion, edema and this leads to low signal on T1 and high signal on T2. However, later on, weeks to month the bone marrow will then be replaced with fat and in some instances perhaps fibrosis and often you can see a very sharp line between what's normal and what's abnormal like in this case, everything above here was the field of radiation, everything below here is where it was normal. It can also look like this and this is a person with radiation to the iliac bone in this case this is much more scurotic and the iliac bone is more deformed. There are technical artifacts and so these are a couple of things that we can see that can mimic things and these are really things that aren't there but based on how we do our imaging it produces things on our studies that make us think that there's actually a lesion there. So one is the hemohead, a lucency. So in internal rotation you can get what looks like a lucent lesion here within the hemohead that will disappear on external rotation. A similar lucency we can see in the radiotuberosity. So here's the radius and here's the bi-symbol radiotuberosity and the lateral view we see this lucent area in there that then disappears on the AP view and this is actually similar concept to the hemohead pseudocyst. Another thing is pulsation artifact. Remember that so this is pretty obvious here we can see that in the knee that we can see the popotel vessel, the artery here and we see the pulsation artifact that runs along through the image. And you might say, all right, I'm not gonna confuse this with pulsation artifact this is so easy to tell. Well, what about this case? Is there a lesion in the fibular head right there? That could look like a lesion but in fact that's actually pulsation artifact from the popotel artery in this case. So it doesn't have to be this traumatic it could be pretty subtle and you just wanna be aware of this when you look at these cases. So pulsation artifact, this is ghosting artifact from pulsatile arterial venous flow and it can mimic lesions. And one of the things that you can fix this is to exchange the phase and frequency encoding directions and to resolve whether or not the lesion is really there. Another MR artifact that we can get is something called the wraparound artifact or aliasing artifact. In this case, here's in the forearm there's actually a fatty lesion like POMA and that's the reason for the MRI study. However, when we did the T2 wave image we see another lucency here and then this doesn't make sense. It's really a lipooma. Why would it be bright on the T2 wave image? Well, in fact, if you look very carefully here's the spine and this was actually a sebaceous cyst that was superimposed upon the arm making it look like there was a that this was a different signal intensity than the lipooma. So in summary, there are many lesions in bone that can be mistaken for a bone tumor. And in fact, many lesions that we see in bone are actually not true tumors. And so bone tumors can be due to a variety of disorders and including imaging artifacts. And you need to have a high index of suspicion and knowledge of these common bone tumor mimickers in order to prevent misdiagnosis and provide the appropriate treatment.