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Marlena Jbara: My name is Marlena Jbara and this lecture is entitled "Imaging Of Soft Tissue Masses Of The Foot And Ankle Part 1." Disclosures: I or related party have no financial relationship to disclose. Objectives: Review imaging tools and recommended guidelines for evaluation of all soft tissue masses of the foot and ankle. I will provide you with the systematic approach to analysis of foot and ankle soft tissue tumors and provide us with an in-depth review of incidence and imaging findings of benign soft tissue tumors of the foot and ankle. In part 2, we will review malignant soft tissue tumors and further go on to review cystic and non-cystic tumor like masses. Okay, to get started, what's in the imaging toolbox. Generally, assessments begin with x-ray. They can move onto CT, MRI or more frequently these days ultrasound. Obtaining x-rays for soft tissue mass, what's the point? Well, the point is that you would want to identify whether there is either pathology, foreign body, fracture, reactive changes in adjacent bones, the presence or absence of periostitis, the presence of fat, the presence of mineralization whether that be osseous, cartilaginous or fibrous.
But of course, we can move onto to CT if we require superior spatial resolution, which is the ability to separate two points in space. Subtle cortical erosions can be identified with subtle calcifications, ossification and matrix mineralization. In ultrasound, we can differentiate cyst versus solid lesions. We can evaluate hyperemia and vascular supply, which may be useful for image-guided biopsy and aspiration. We can help to characterize sub-masses including lipomas, vascular lesions we can tell what Doppler, we can have very exquisite sensitive modalities to detect whether or not a lesion has vascularity. We can look at nerve sheath tumors and I identified the nerve and lesions within it. And of course, this is operative dependent and really requires radiologic expertise and time. The America College of Radiology provides appropriateness criteria for soft tissue masses and a summary of their recommendations include that the initial imaging study for superficial or palpable soft tissue masses should be x-rays. Ultrasound is equally appropriate for small lesions that are superficial to the deep fascia. For deep masses, the lesions in areas are difficult to evaluate radiographically like the groin, paraspinal lesion, deep soft tissues of the hands and feet or flank. Radiographs are also usually appropriate. And if the initial evaluation of soft tissue masses isn't diagnostic, further evaluation with MRI without and with IV contrast or MRI without IV contrast is usually appropriate.
In patients presenting with spontaneous hemorrhage or suspicion of vascular mass, if the initial evaluation is non-diagnostic, further evaluation with either MRI without and with IV contrast or CT without or with IV contrast is usually appropriate. If the initial evaluation of a soft tissue mass isn't diagnostic in patients who are non-MRI compatible or who have metal limiting MRI evaluation, CT with IV contrast or CT without and with IV contrast is usually appropriate as the next imaging study. Of course, with MRI we have superior soft tissue contrast. The lesion signal intensity can be determined and we can actually figure out some of what the amino acid make up might be. We can use contrast to determine enhancement. Of course, we can see the leads in location and provide information for preoperative planning, the tumor proximity to neurovascular structures. In the imaging toolbox, the America College of Radiology has determined charts to figure out the appropriateness category of certain imaging test in order to properly guide utilization and get us to the answer in the least amount of time. So in variant one, a soft tissue mass may be superficial or palpable, the initial imaging study is that an x-ray and an ultrasound are usually appropriate and the remaining may not be appropriate as the initial imaging study.
Moving on to soft tissue masses, non-superficial or nonspecific clinical assessment can be located in an area difficult to adequately evaluate it with radiographs. You usually begin with an x-ray and an ultrasound may be appropriate and may be then appropriate to either go to on MRI or CT as an area of interest to determine what the lesion would be. For soft tissue masses that aren't diagnostic in their initial evaluation, the next imaging study might be an MRI with or without IV contrast or an MRI without IV contrast. That may be appropriate in the setting a non-diagnostic initial evaluation with ultrasound. And of course, soft tissue mass that has a non-diagnostic initial evaluation, and then presents with spontaneous hemorrhage and MRI with contrast or CT is going to be usually appropriate in that category. And then lastly, those patients that aren't MRI compatible or with metal have usually appropriate indications for obtaining a CT at the area of interest with IV or without and with IV contrast. In MRI, we will be looking at the T1 weighting to determine fat signal, the T2 weighting to determine fluid signal. We will be looking towards contrast enhancement to determine central or peripheral enhancement and then peripheral enhancement where usually thinking that this is a smooth, thin versus a thick irregular; those would be our descriptors. There can be homogenous and heterogeneous enhancement, dynamic enhancement, can either be early or late.
We can have special imaging features that include the tail sign and target sign that can be seen in neuropathic or neural tumors. Characteristic location of enhancement may tell us whether it's in bursa and then of course associated anatomy, the tendon nerve vessel, plantar fascia or joint we can see with excellent soft tissue contrast. MRI signal intensities, we can see high signal and T1 weighted images. In fact, the presence of proteinaceous fluid, the presence of methemoglobin, of course melanin seen in melanoma and gadolinium. Low signal in T2 weighted images includes calcification, fibrous tissue or scar with low water content or fibrous tissue and fibrous neoplasms and of course within hemosiderin. Again, the MR signal intensities of various tissues are labeled throughout charts and tissues such as hematoma may have a high T1 weighted image secondary to the methemoglobin and also high T2 weighting. Fatty signal and fatty marrow will of course have high T1 weighting and intermediate or low T2 signal weighting. Muscles, nerves, hyaline cartilage these can all be intermediate T1 and T2 signal intensities. Cortical bone, tendons, ligaments, fibrocartilage, scar tissue and air are generally of low T1 signal intensity with elevated T2 signal intensities. Hematopoietic marrow can be of low signal intensity whereas fluid can be of high T2 signal intensity. Hemangiomas with their flow voids can have an intermediate T1 signal intensity and an elevated T2 signal intensity.
So in this talk, we are going to discuss the benign soft tissue tumors such as plantar fibromatosis, xanthomas, tenosynovial joints or tumors of the tendon sheath. We will talk about hemangiomas and lymphangiomas, lipomas, angiolipomas, soft tissue chondromas, and synovial osteochondromatosis, peripheral nerve sheath tumors and a glomus tumor. So to begin plantar fibromatosis also known as Ledderhose's disease is a benign fibroblastic proliferation of the plantar fascia. It has a male-to-female predominance of approximately two to one and is seen bilaterally in about 20% to 50%. On ultrasound, this is often seen by hypoechoic to mixed echogenicity. There may be discrete fusiform, multinodular thickening of the plantar fascia. Here we can see two ultrasound examples on the right demonstrating this fusiform hypoechoic lesion inseparable from the cord of plantar fascia in this patient who is being imaged from the palmar or sole surface. In transaxial imaging, we can see when we turned the probe 90 degrees, we have this hypoechoic lesion that demonstrates increased through transmission and inseparable from the plantar fascia. Of course, on MRI signal characteristics will include low water contents. So on T1 weighted images, iso to low signal compared with the adjacent muscle. On post-contrast imaging, with gadolinium there may be variable contrast enhancement.
It can enhance, it does not have to enhance, or it has high and low signals. And on T2, it's generally low-to-intermediate signal compared to skeletal muscle being that it has a very low water content. In this MRI recent example, I had a plantar fibromatosis, the patient came in with the feeling of a palpable mass, which is now indicated and marked by vitamin E capsules. Vitamin E contains fat and therefore can be seen on T1 weighted images that are searching for fat. And what you can see here is this fusiform nodule adjacent to the hallux metatarsal neck region extending an inseparable from the abductor hallucis distal fascia towards the skin surface. On the transaxial T1 weighted image at the top right, we can see this isointense to skeletal muscle nodular lesion also of low signal intensity in the middle image on a short axis T2 weighted image. And of course, transaxial T1 post-contrast imaging demonstrating fuse enhancement in this patient with plantar fibromatosis. And furthermore another example of plantar fibromatosis, we can see in these transaxial images cone down to the medial fore foot where we can see this nodular excrescence extending from the distal plantar fascia and you can see this on the transaxial T1 and non-fat suppressed T2 weighted image and of course on post-contrast enhanced image of the bottom, you can see no enhancement at this plantar fibromatosis nodule.
Moving on to Achilles tendon xanthomas, these are painless soft tissue masses. They occur most commonly at the distal third of the tendon. There are usually bilaterally and symmetric. They represent an accumulation of lipid-laden macrophages, inflammatory cells and giant cell secondary to cholesterol deposition and tissues. The majority are caused by familial hypercholesterolemia, type 2 and 3 hypoproteinemia and cerebrotendinous xanthomatosis. On x-rays, we can see soft tissue densities in the Achilles tendon. On ultrasound, this may show an area of thickening in the anteroposterior dimension of the tendon, which is normally about 7 mm in male and about 6 mm in females and you lose the normal tendon striation and replace that with multiple hypoechoic foci within the tendon itself. Achilles tendon xanthomas can be seen on MRI again as an increased AP diameter of the tendon. They can be hyperintense on T1 and T2 weighted imaging. There is loss of the normal anterior concavity of the tendon. There can be a speckled appearance of the tendon and focal thickening of the tendon seen. An here we can see on these examples at the bottom left of this fusiform Achilles tendon enlargement with hyperintense signal change within the tendon on both T1 at the bottom left and here on T2 at the upper right and you can see the fusiform enlargement with associated paratenonitis in the adjacent Kager fat triangle.
On transaxial image at the bottom right, we can see the fusiform enlargement again of the Achilles tendon with the nodular high signal lesion at the anterior most aspect of the Achilles tendon, Achilles tendon xanthoma. Moving on to tenosynovial giant cell tumors of the tendon sheath, these are also known as giant cell tumors of the tendon sheath, pigmented villonodular tumor of the tendon sheath, extra-articular pigmented villonodular tumor of the tendon sheath or localized/fibrous focal nodular synovitis. There could be localized and diffused forms and it's most common in the third to fifth decades of life. On x-ray, we can see pressure erosions of the underlying bone in about 10% to 20% of cases and the mass itself is of soft tissue density. Periosteal reaction and calcifications are uncommon. On ultrasound, we can not only allow the characterization of the lesion but it's also able to demonstrate the relationship with the adjacent tendons. Associated with the volar surface of the digits, these lesions don't move with flexion or extension of the adjacent tendons. They are usually homogenously hypoechoic, although some heterogeneity may be seen in an echo texture and minority of cases. Most of these lesions will have internal vascularity. And here we can see four representative transaxial images through the ankle demonstrating this exophytic mass extending from the medial aspect of the talus, which can be seen here with surrounding hyperintense change on the T2 weighted images at the bottom center and right.
Notice the increased low signal as well that's seen on the T2 weighted image and this is a result of the blooming that's present within the hemosiderin laden macrophages within this lesion. Furthermore, on these two left-sided sagittal representative images, you can see along the posterior tibial tendon sheath at the top, you have these focal areas of lower signal, which demonstrate blooming. At the bottom left, you can see the fluid surrounding signal in this example on T2 weighted image and of course the coronal image demonstrating this exophytic mass from the medial aspect of the talus consistent with tenosynovial giant cell tumor of the posterior tibial tendon sheath. Tenosynovial giant cell tumor of the tendon sheath, the MR signal characteristics generally include T1 low signal. There can also be of low signal T2 weighted imaging depending on the presence of mineralization and when we inject with contrast gadolinium often shows moderate enhancement. On gradient echo imaging, we are looking for low signal and this is the sequence where we can mostly characteristically demonstrate blooming. So blooming is an artifact by the iron molecule within the hemosiderin macrophage. And we take advantage of this property on gradient echo image to watch this lesion bloom knowing that it contains this blood product often seen in tenosynovial giant cell tumors of the tendon sheath.
Moving on to hemangiomas, these are benign tumors of vascular origin. Based on the vessel type, we can further characterize them into capillary, cavernous venous or arterial venous. X-rays are important because we will be looking for phlebolith, which represent focal dystrophic mineralization within the thrombus. In up to 50% of cavernous hemangiomas, we have phlebolith present and we can see in this cavernous hemangioma identified in A and B on T1 and T2 weighed imaging that there is some serpentine lesions that are of high T1 and T2 signal. For lipomas, MRI is the modality of choice. Lipomas follow subcutaneous fat signal on all pulse sequences and we can see here that high signal on T1 weighted image on this image to the left A. It saturates on image B on all fat saturated sequences and there is no enhancement identified on lipomas. On T2 imaging, it's usually of high signal. It saturates on fat saturated sequences and persistent areas of T2 would be considered nodules or septations and they may indicate the need to further image with contrast and see if those nodules are actually enhancing for liposarcomas.
Soft tissue chondromas represent benign extraosseous extra synovial soft tissue tumors composed predominantly of mature hyaline cartilage. The majority of soft tissue chondromas arise on the finger enhanced followed by the toes and feet. On MR imaging, we have high T2 signal typical of chondroid lesions, may have small signal voids owing to the matrix calcifications and it mimics chondrosarcoma as can be seen here in this soft tissue chondroma at the plantar aspect of second interspace where there is a lesion in the soft tissues demonstrating intermediate to hypointense change and here seen on T2 weighted images as a hyperintense, heterogeneous lesion in this soft tissue chondroma. Another example of a soft tissue chondroma can be seen here at the plantar lateral subcutaneous soft tissues. This is inseparable from the plantar fascia as well. The differential diagnosis would include a fibroma. Of course, the intense elevated signal on proton density makes us suspect that this is actually hyaline cartilage, and therefore biopsy reveals soft tissue chondroma in this case of this plantar lateral subcutaneous soft tissue chondroma. Moving on to this great example of synovial osteochondromatosis, this represents a benign monoarticular disorder of unknown origin that's characterized by synovial metaplasia and proliferation resulting in multiple intraarticular cartilaginous loose bodies of relatively similar size not all of which are ossifying.
This generally occurs in the fourth to fifth decades of life and the adjacent bone typically has erosions. The main differential diagnosis includes PDNS, which typically loads low MR signal and blooming. Bodies are generally low on T1 and high signal T2 weighted images composed of hyaline cartilage and most commonly occurring at the knee, about 50% of them occur there. The involved synovium typically enhances, and here we can see on this example of this sagittal x-ray, this lateral x-ray is seeing these multiple joined bodies at the anterior joint line and here you can see on this transaxial T2 fat-suppressed images, these multiple intraarticular joint bodies have relatively similar size demonstrating hyperintense change and bone erosion. Moving onto peripheral nerve sheet tumors, this represents 10% of all foot and ankle tumors. Schwannomas, neurofibromas, and malignant peripheral nerve tumors are in this category, the most common being Schwannoma at 57%. Schwannomas and neurofibromas are benign with the slow growth rate and in the lower limb the posterior tibial nerve, the PTN is most commonly involves and here we can see an example of the split fat pad sign and you can see it on ultrasound here where you see this the nerve, the posterior tibial nerve enlarging to form this fusiform hypoechoic mass but increased through transmission. Here, we can see on this coronal image, this splitting of the fat as it dives between these T1 planes along the course of the nerve and you could see the tail of the never coming out here. Further peripheral nerve sheet tumors can demonstrate a target sign, which is diagnostic for a peripheral nerve sheet tumor, but we can't always tell whether it's seen in Schwannomas, neurofibromas or malignant peripheral nerve sheet tumors.
And we can see here on this example to the top left of this peripheral hyperintense T2 weighted signal with central low signal and here, you can see on the transaxial T1, T2 and the coronal T1 fat-suppressed image through the abducted digiti minimi, the target sign. The glomus tumor is an interesting tumor. It's a hamartoma that arises from the glomus body. It's an arterial venous shunt within the dermis that contributes to temperature regulation of the fingers. Lesions of this hamartomatous body can be pain. It can be point tenderness and cold hypersensitivity. It's most common in females and lesions are most common in females in the third and fourth decade. There are multiple in about 10% of cases. The MRI is significant in that it demonstrates the typical low signal intensity of lesions on T1 weighted images. T2 would demonstrate high signal intensity and here you can see on this post-contrast gadolinium enhanced image on B, it's uniform enhancement due to the high level of vascularity seen in these glomus tumors. In summary, this tutorial provided an overview of imaging tools used to assess soft tissue tumors of the foot and ankle. We reviewed general principles of MR evaluation of soft tissue tumors including attention to signal, the presence of enhancement with gadolinium and the relationship with the lesion of the location and proximity to adjacent structures.
I have presented to you with an overview of the most common, benign soft tissue tumors of the foot and ankle. These references are available for your review. Thank you for your time and generous attention.
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