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Marlena Jbara: In this session, we will discuss bone tumors of the foot and ankle part 2. Disclosures: I or related parties have no financial relationship to disclose. Objectives: We will review specific principles of imaging evaluation of the most common benign bone tumors of the foot and ankle. We will look at the morphology, age, matrix and location. We are going to review the classification and staging of benign bone tumors of the foot and ankle. And lastly, we will provide an evaluation of the most common benign bone tumors of the foot and ankle. So the evaluation of the benign bone neoplasm starts with an algorithm that includes morphology. We can look at the border of the lesion, identify the presence or absence of bone destruction, the presence of periosteal reaction, the presence of matrix and osseous, fibrous or cartilaginous matrix, the presence of absence of the soft tissue mass. We will look at the age and sex of the patient to determine the likely etiology of bone lesion. Whether or not it's single or multiple may give us a clue. The location in the particular bone, what part of the bone, is it the epiphysis, metaphysis or diaphysis? Is it central within the bone or eccentric? The location in the skeleton, what bone is involved?
We can use schematic such as the one on the right to determine that whether or not something has a cartilaginous matrix, whether or not there is Heron and type of periosteal reaction, whether there is a geographic lesion or moth-eaten or permeative, whether there is soft tissue extension, and of course the multiplicity of these lesions. Geographic bone destruction deals with looking at the type of margin around the lesion. So a geographic 1A as seen in this schematic on the bottom right is a thick complete sclerotic margin, an indolent lesion. In 1B, it's a thin and incomplete active lesion. And for 1C, it's no sclerotic margin and you barely can see anything except that there is a lytic lesion and you walk from the normal to the abnormal bone. These are generally aggressive lesions. So if it's slower growing, it could be sharply aligned with the sclerotic border and it's giving what's called a narrow zone of transition. In the aggressive lesions, it's a poorly-defined border and a wide zone of transition. Aggressive, malignant lesions generally have this wide zone of transition. Benign bone tumors include radiographic grading by Campanacci, which demonstrates grade 1, 2 and 3 lesions being whether they are quiescent, well-defined margin with surrounding sclerosis. The cortex are slightly thin but no deformed. Grade 2 are active lesions where there is a well-defined margin that lacks sclerosis.
The cortex may be thin and expanded. And grade 3 represents aggressive lesions, ill-defined margin often with cortical destruction and soft tissue extension. The staging of bone tumors also by Enneking gives a similar classification where stage 1 are latent lesions, stage 2 are active lesions, and stage 3 are aggressive lesions. These are the common benign bone tumors of the foot and ankle that we will be discussing. So let's start with an intraosseous ganglion. This is a benign subchondral radiolucent lesion without degenerative arthritis. The epidemiology is that they tend to occur in middle age and they may present with mild localized pain. They could be uni or multilocular cyst surrounded by a fibrous lining containing a gelatinous viscous material. The origin of ganglions are mucoid degeneration of intraosseous or intraosseous connective tissues, may be due to trauma, ischemia. Penetration of juxta-osseous soft tissue ganglion or synovial herniation occurs into an underlying bone. And common locations are the epiphysis of long bones, the medial malleolus, the femoral head or neck, the proximal tibia, carpal bones, subarticular flap bones such as the acetabulum. And here in this example we can see this intraosseous ganglion on the x-ray as basically a well-defined geographic 1A lobulated lesion with thin fenestration of cortex at its most medial border, which is overlapping on the third metatarsal.
Much better delineated on this companion long axis image through the CAT scan demonstrating this lucent lesion creating endosteal scalloping and bubbly appearance of an intraosseous ganglion. Further MRI demonstrating on this image on the left, which is T1 weighted noted fatty marrow as bright. The asterixis over the intraosseous ganglion seen at the base of the fourth metatarsal. Here, we see on the fluid sensitive image, the lobulated high signal and of course the post contrast imaging demonstrating this majority of the lesion not enhancing with its viscous gelatinous myxoid degenerative material with this thin enhancing high signal rim as denoted by the arrowheads. Intraosseous ganglion. Moving on to an extremely common lesion, the non-ossifying fibroma, this is a well-circumscribed solitary fibrous proliferation. The age and sex of the patient are generally less than 30 with the highest frequency in the second decade of life and there may be reports of up to about 35% of all children have these non-ossifying fibromas. These are typically considered do-not-touch lesions and we chase them so you can identify them and we cannot do interventions that aren't necessary. At time, if there are certain size, they may present with a pathologic fracture.
And then it may be necessary to intervene and enucleate the lesion and pack it with methyl methacrylate. The radiology includes an eccentric lobulated trabecular pattern generally a subcortical lesion with central lucency. There is scallops, sclerotic margins that are very well-defined. There is no periosteal reaction in the absence of a pathologic fracture. The key to the diagnosis is that it's a younger patient. It's cortically based or intracortical. It generally occurs in the metaphysis and grows towards the diaphysis with the growing skeleton. There are lobulated trabeculae and it has sclerotic well-defined borders, non-ossifying fibroma. And non-ossifying fibromas can be seen here at the distal lateral femur. Notice the large long intracortical bubbly lucent lesion with well-defined geographic sclerotic rim. On the central example, notice the endosteal sclerosis along this non-ossifying fibroma, which is beginning to ossify, and of course this lesion on the right being this bubbly intracortical lucent lesion that's displacing the cortex and widening the space helping us to determine that this is indeed an intracortical lesion. And here is a nice example of non-ossifying fibromas and the natural history of them filling in with bone. Here in this example, in 2002, this child has this lateral metadiaphyseal intracortical lucent bubbly lesion with a pretty thick rind of sclerosis at this point.
Then this rind of sclerosis fills in and begins to fill in further within five months later this year. And of course, six months later we can see that there is nearly complete filling in of this now ossifying fibroma. Moving on to intraosseous lipomas, the epidemiology of these lesions is from 5 to 85 years of age. The peak incidents occurring in the fourth to fifth decades of life. The clinical presentation is approximately 70% present with pain, approximately 30% of these are incidental. There is a predilection for the lower limb, which is about 71%. The calcaneus is involved approximately 32% of the time and it's considered the most frequent calcaneal bone lesion. The femur is implicated in 20% especially the intertrochanteric region. The tibia followed by fibula from 13% to 6% as you can see here upper limb 7%, skull and mandible 7%, spine and pelvis 12% and the ribs 2.5%. Treatment and prognosis: Intraosseous lipomas that don't affect bone stability can be treated conservatively and cases of course with eminent fractures are treated by curettage and bone grafting. And the differential diagnosis in the calcaneus is a unicameral bone cyst, a UBC. This is a lateral film demonstrating an intraosseous lipoma at the talar dome in this case.
We can see the presence of elevated T1 signal in this intraosseous lipoma of the talus demonstrated on T1 weighted images and we can see using fat suppression on T2 weighted images that a portion of this lesion suppresses proving the presence of fat within the lesion. And that's what we need to identify to make the diagnosis of an intraosseous lipoma. Moving on to unicameral bone cyst, the epidemiology of this lesion occurs in the first to second decades of life. About 65% occur in the teenagers and then more common in males with a male-to-female predilection of about 2 to 3 to 1. The clinical presentation is generally either asymptomatic or presents with a pathologic fracture. The locations include intramedullary and metaphyseal of the long bones and generally about the growth plate. The proximal humerus is the most common location accounting for about 50% to 60% and proximal femur about 30%. Rarely, we can see this in an adult in unusual locations such as talus, calcaneus or even the iliac wing. And the fallen fragment sign is a reliable sign to see if there is a fracture through a unicameral bone cyst in a long bone, you may identify a dependent bony fragment that's layering on top of the central gelatinous fluid of the unicameral bone cyst. Unicameral bone cyst can be seen here on this lateral x-ray as a lucent lesion at the calcaneal body deep to the angle of Gissane.
We can see here unicameral bone cyst. Another example of unicameral bone cyst demonstrating the remnant internal trabecular of this cystic lesion. And here is an MR cartilage for that example demonstrating the high signal calcaneal lesion, namely simple bone cyst. Note the lobulated borders in the endosteal scalloping that's occurring in this long axis image through the calcaneus. Moving on to aneurysmal bone cyst, the epidemiology is at the proximally 80% of these occur in children less than 20 years of age. The presentation is variable. It can go from a dull insidious ache to acute pain and if there is a pathologic fracture, there is definitely going to be pain. The pathology is a shelled out medullary spaces filled with blood and fine-needle aspiration is usually not diagnostic and is dominated by fresh blood. Although these lesions are often primary up to a third [indecipherable] [15:24] are secondary to an underlying lesion. For example, chondroblastoma, fibrous dysplasia, giant cell tumors and osteosarcoma. Here, we can see a few examples on the right. Notice the lytic lesion in the posterior calcaneus identified on the x-ray. Much better seen on the companion CT at the top right. What's really impressive on the image of B is the typical fluid level seen in aneurysmal bone cyst, which we are trying to identify in a variety of different ways.
Aneurysmal bone cyst: The location is eccentric located in the metaphysis generally of long bones adjacent to an unfused growth plate. That is the most common location in long bones at about 50% to 60% and those occurring in the lower limb account for about 40% of them. In the tibia and fibula especially the proximal tibia that's about 24%, the femur 13% especially proximally. In the upper limb, it's about 20% and the spine and sacrum about 20 to 30%. Here is a nice example of an aneurysmal bone cyst. Of course, this x-ray demonstrates a heterogeneous lucent lesion of the calcaneus. An aneurysmal bone cyst on x-ray can be sharply defined or can have expansile osteolytic margins. In nuclear medicine, we can use the dough nut sign, which is increased up take peripherally with a photopenic center. But in MRI and CT, the main [indecipherable] [17:25] fluid-fluids levels and of course lesions that contain fluid-fluids levels might be giant cell tumors. In the differential diagnosis, we can also include chondroblastoma, simple bone cyst and telangiectatic osteosarcomas. A nice example of an aneurysmal bone cyst again in the calcaneus with the fluid-fluids level identified both on T1 and T2 weighted imaging denoting the separation of blood products.
Aneurysmal bone cysts are usually treated operatively with curettage and bone grafting with a recurrence rate of about 20% and percutaneous treatment with fibrosing agents has also been performed either in isolation or as a precursor to surgical excision. Spontaneous regression may occur including following partial removal but that is not typically the natural history of this lesion. Osteoid osteomas, 10% of all benign bone lesions. Generally, there is nocturnal pain that's relieved with rest or salicylates. It's composed of a nidus lesion, which is a vascular tangle with a fibrovascular rim and then a reactive surrounding phase of sclerosis. The distribution is usually cortical. When in the talus, it can also be sub-periosteal. 60% to 80% of these lesions occur on long bones, most commonly in the femur and mid diaphysis. Approximately, 20% in the phalanges and 10% in the posterior elements of the spine. CT is your modality of choice. In nuclear medicine, we can see a double density sign, which is a hotter spot within a hot area sign. An MRI is sensitive but not specific for the lesion. The treatment will include radiofrequency ablation and the differential diagnosis includes Brodie's abscess, osteoblastoma when they are greater than 2 cm in size, stress fractures and of course cortical desmoids. Here is a nice example of an osteoid osteoma. Here, we can see on the CAT scan, the best example of this lytic nidus within the calcaneus.
Notice on the plain film, we are only seeing a band of sclerosis, which for all intensive purposes that I would have called the stress fracture. But we can see on the MRI on this sagittal T1 weighted image noting the low signal throughout the anterior calcaneus and here we can see the vascular nidus as identified on this T2 weighted image on the right. Moving on to osteoblastoma, this represents 1% to 3% of all bone tumors. The male-to-female ratio is about 2.5 to 1 and there is minimal response to aspirin with dull pain at night. The lesions are larger typically than 2 cm and the distribution is in the spinal column about 40% often involving the posterior column. In the cervical spine, that represents about 9% to 39% of all spinal lesions and the sacrum 17%. These are usually located in the metaphysis and distal diaphysis of the long bones. Osteoblastoma on x-ray may be lytic with reactive surrounding sclerosis. They can be expansile, possibly secondary to associated aneurysmal bone cyst. In CT, there is predominantly lytic with internal matrix better identified. In MRI, we may see low T1 and an elevated T2 typical pattern of a flare phenomenon, which is high signal seen in the surrounding tissues and of course it enhances. The treatment is radical surgical excision possibly preoperative embolization as these lesions tend to bleed. An example of osteoblastoma, we can see this irregular area of the talar neck better seen in the cone down view.
This is an old case. Here, we can see this osteoblastoma with this fungating mass on the sagittal T1 and then central T2 and of course post-contrast lesion larger than 2 cm heterogeneous replacing most of the talus. Moving on to chondroblastoma, these are rare representing less than 1% of all bone tumors. Sometimes, they masquerade with secondary aneurysmal bone cyst. The age and sex distribution, they are more common in men occurring in the second to third decade. Clinically, you can have pain, swelling and joint manifestations and the most common location includes the epiphysis of long bones with 70% occurring in the humerus, femur and tibia, 10% are found in the hands and feet. Here, in this example on the right, notice this geographic subarticular lesion. This was a chondroblastoma. Here is another example at the bottom. Two pictures that AP and oblique image demonstrating this lytic lesion with pathologic fractures to the talar dome representing a chondroblastoma. And this lesion can be barely seen on the lateral projection. Here we can see a chondroblastoma noting the fluid levels that you can see there and this lesion occupying the majority of the talus, the talar dome and neck.
Moving onto chondromyxoid fibroma, this represents less than 1% of bone tumors. The male-to-female predominance is two to one. These are mostly in teenagers. They present with indolent pain with eccentric lytic metaphyseal lesion. No calcified matrix. They often look like non-ossifying fibromas and that they can be eccentric, elongated and have endosteal sclerosis and coarse trabeculations. They can also be slightly expansile. The lesion curettage but recurrence might be common and of course that can be en bloc excision as treatment for chondromyxoid fibroma. An example of a chondromyxoid fibroma here we have this long axis AP view of the foot demonstrating this lytic lesion at the base of the second metatarsal. Looking at this example to the upper right, we can see this geographic replacement of the underlying bone by this heterogeneous lesion with areas of increased and decreased signal in T1 and T2 weighted imaging of chondromyxoid fibroma. Enchondromas: Generally, these lesions can be solitary in the 20 to 40 year age category, but when you see them in a young adult, think about the possibility of multiple enchondromas. These represent 12% to 25% of all benign bone tumors. They may have calcification or actually chondroid matrix except when you see them in the phalanges. In the absence of pathologic fracture, you will not see periosteal reaction. There can be endosteal scalloping and if there is pain, think malignancy.
So in the presence of Ollier's and Maffucci's, the multiplicity of lesions increases the overall risk to develop malignancy in any one particular lesion. The pathophysiology includes ectopic Hyaline cartilage rest and the theory is that there is displacement from the growth plate in the intramedullary bone. The location is generally central and intramedullary and 50% of solitary enchondromas occur in the hands and feet. Metaphyseal locations in the proximal and distal femur and the proximal humerus and pelvis make up the remaining. And here we can see these examples of enchondromas. Both of them in the proximal phalanges. Note the cortical break at the example on the top with a pathologic fracture and of course we have this expansile lesion in the metaphysis in the skeletally immature patient at the bottom right. Further enchondroma, we can see -- we can barely perceive it on the x-ray and the base of the third proximal phalanx. However, in the central image and image to the right, there is T1 weighted low signal and T2 weighted elevated signal intensity relative to the skeletal muscle in this enchondroma. And there is a spectrum of enchondromas. Of course, the cartilaginous matrix can be seen here and the example of this finger on the metacarpal neck with pathologic fracture. We can see this stippled flocculent or ring-and-arch matrix seen in the central image and then its cross-section. On MRI, it has similar morphologies being flocculent and ring-and-arch like demonstrating low T1 and heterogeneous elevated T2 signal.
In enchondromatosis and Ollier's, we have multiple enchondromas. This represents a rare non-hereditary form of enchondromatosis, which is predominantly [indecipherable] [28:19] on one side of the body and the risk of malignancy has been reported to as high as 30%. In Maffucci's, this is enchondromatosis with soft tissue hemangioma. There is even high risk of malignancy based on the increased malignant right at the hemangioma as the vascular tumors. Distribution is similar in the small tubular bones of the hands and feet up to about 50% and of course still afflicting the large tubular bones of the femur, tibia and humerus. And here is a nice example of multiple enchondromas forming deformed phalanges and metacarpals even distal radius and ulna. Moving on to osteochondroma, this represents 10% to 15% of all bone tumors, 35% of all benign bone tumors, and malignant transformation of the cartilage cap is what we are concerned with. It's about less than 1% in the solitary lesion but those patients who have hereditary multifocal exostoses can have as high as 25% malignant rates. Another name for MHE is a diaphyseal aclasis. Indications for surgery of course include malignant transformation or the compression of adjacent structures by one of these growing lesions. Osteochondroma, the x-ray of the lesion must be contiguous with the medullary canal and we can see here. It can be difficult to determine that in the talus but on the frontal view I can think you can appreciate along the lateral talus, the exophytic margin of this cauliflower like lesion.
The MRI identified at the bottom right is the transaxial view and it's best to see the chondral cap more than 1.5 cm thickening of the cartilage cap is suspicious for malignancy. More example of osteochondroma seen here with this distal tibial lesion contiguous with the medullary canal. Transaxial T1 weighted and sagittal STIR imaging demonstrating the cartilage cap and of course the en bloc resected specimen demonstrating the chondral cap with the asterisks in this osteochondroma. A companion case to osteochondroma include the subungal exostoses, which can occur under the nail bed exophytically growing and causing a great deal of pain to the patient. Here we can see in this lateral x-ray, the osteochondroma or subungal exostoses and the CT lesion demonstrating contiguity with the cortex. Now, of course, MRI demonstrating the subungal location of this exostoses. Companion case of periosteal chondroma, we have a cartilage producing lesion that's a surface lesion from the cartilage and causing the exophytic mass to displace the second proximal phalanx. Here in this companion case of a 00:31:49 _____ lesion, we have this BPAP or bizarre parosteal osteochondromatous proliferation where we can see the mineralization along the middle phalanx.
Moving on to giant cell tumors, these represent non-mineralized eccentric lytic meta-epiphyseal lesions that usually involve the long bone. Histologically, there is a large number of multi-nucleated osteoclastic giant cells in the background of mononuclear cells and the spindle cells stroma. These represent 18% to 23% of benign bone neoplasms and occur when the growth plate is closed. Approximately, 80% of them are between 20 and 50 years and secondary aneurysmal bone cysts are most common. The location around the knee, the distal femur most commonly 50% to 65%. Of course, the distal radius accounts of 10% to 12% and these are generally considered possibly more malignant. In the sacrum, these lesions account for about 4% to 9% and vertebral bodies as well. General rules for giant cell tumors, these represent closed epiphysis and occur only with a closed growth plate. The lesion extends to the subchondral bone and abuts the articular surface. Approximately 84% to 99% come within 1 cm of the articular surface. Thirdly, eccentric lesions if they are large may be difficult to assess and lastly sharply defined non-sclerotic zone of transition is what we are looking for, well-defined with a non-sclerotic margin geographic 1C, although approximately 5% of these lesions may show some sclerosis. Here is a nice example of a giant cell tumor, a subarticular x-ray identified as the left with this lucent lesion with no real zone of transition and here we can see on the transaxial CAT scan the well-defined lytic subarticular lesion.
And here on these MRI representative images, you can see on T1 weighted imaging there being fluid-fluid level that are hyperintense to skeletal muscle, some heterogeneous T1 signal. And of course, on T2 we can clearly see now the fluid-fluid level in this lesion subarticular biopsy proven giant cell tumor. Another example of giant cell tumor in the hand notice the lack of sclerosis or border in this lytic lesion replacing the index metacarpal head and neck. And in summary, I have provided an imaging approach to bone tumors of the foot and ankle. We reviewed specific principles of imaging evaluation of the most common benign bone tumors of the foot and ankle. The morphology, age, matrix and location, we evaluated the most common benign bone tumors of the foot and ankle during this 30-minute session, namely non-ossifying fibroma, intraosseous ganglia, intraosseous lipoma. We reviewed simple bone cyst, aneurysmal bone cyst. We looked at osteoid osteomas, osteoblastoma, chondroblastoma, chondromyxoid fibromas. We reviewed cartilage lesions of enchondromas, osteochondroma. We looked at subungal exostoses and giant cell tumors and references are available. Thank you for the generosity of your time and attention and hope that this lecture has been of value for you. Thanks again.
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