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Marlena Jbara: My name is Marlena Jbara and I am a radiologist from Staten Island University Hospital at Northwell Health. In this tutorial, we will be discussing imaging of soft tissue masses of the foot and ankle part 2. Disclosures: I or related party have no financial relationship to disclose. The objectives of this lecture will be to review malignant soft tissue tumors. We will go on to review cystic tumor like masses of the foot and ankle and then lastly, we will review non-cystic tumor-like masses. The entities we will be discussing under malignant soft tissue tumors include synovial sarcoma, malignant fibrous histiocytoma, previously known as fibrosarcoma. We will discuss epithelioid sarcoma (ES), clear cell sarcoma, bone metastasis with rare mention of leiomyosarcomas, liposarcomas and rhabdomyosarcoma because these are extremely rare. Let's begin with synovial sarcoma. This is typically present in adolescence and young adults ages 15 to 40 years of age. It's typically a slowly enlarging soft tissue mass, which might have been noted for some years and gives a false impression of a benign process.

[02:00]

It's a soft tissue mass that's near but not in a joint in a young patient that's about 15 to 40 years of age. There may be the presence of dystrophic calcifications and those are found in up to one-third of cases. You can see fluid-fluid levels on imaging in about 10% to 25% of cases and there can be mineralization on the x-ray in a good percentage of cases. And here are three representative examples in magnetic resonance imaging clinics demonstrating this soft tissue mass that's insinuating between the second and third digits and we can see here on this long axis T1 weighted image through the forefoot, the curved arrow is pointing towards a low signal structure, which represents calcification where the arrowheads are denoting the surrounding soft tissue mass that's splaying the distance between the second and third toes. We can see here on the middle image that we have this hyperintense heterogenous lesions splaying the second and third toes with areas of lower signal intensity seen within it corresponding to the calcium, which you can finally see on this long axis frontal projection of the foot demonstrating soft tissue density containing calcifications and mass effects splaying the second and third toes in this patient with synovial sarcoma. In synovial sarcoma, MRI is the modality of choice to stage the tumor locally. There is a triple signal sign with a markedly heterogenous appearance of synovial cell sarcomas on fluid sensitive sequences. Necrosis and cystic degeneration will ensue with extremely high signal.

[04:00]

Intermediate high signal soft tissue malignant components will be present. And areas of low signal intensity due to dystrophic calcifications and fibrotic bands are present. There can be a bowl of grapes, which is a high tendency of the lesions to bleed sign with fluid-fluid levels. On post contrast gadolinium, there is enhancement and it's usually prominent, can be a diffuse homogenous pattern in about 40% or heterogeneous in about 40% with peripheral enhancement in about 20%. And here we can see on these two representative images, this example to the top right we are seeing on this transaxial T2 non-fat suppressed image that we have this heterogeneous lesion occupying the muscular compartment displacing the tendons peripherally with multiple heterogeneous signal intensities. On this example on the bottom right on this transaxial view through the ankle joint, we can see this soft tissue homogenous mass more regular in this person with synovial sarcoma. Two more images for a synovial sarcomatous mass seen here on a coronal proton density where we see this large deep soft tissue mass of flexor digitorum brevis and longus musculature, very homogenous and regular and here on T2 weighted images, notice the lobulated well-circumscribed borders and relatively non-aggressive appearance of the mass. Malignant fibers histiocytoma, adults range from 32 to 80 years of age with a mean of about 59 years. There is a slight male predilection with a male-to-female ratio of about 1.2 to 1.

[06:02]

This is also known as pleomorphic undifferentiated sarcoma or fibrosarcoma and this represents a painless enlarging palpable mass. Most malignant fibrous histiocytoma are of high grade, 3s and 4s of presentation and are aggressive. They frequently metastasize, approximately 30% to 50% of diagnosis have metastasized and they locally reoccur despite aggressive treatments. The overall five-year survival is between 25% and 70%. Here, I am demonstrating these images on this transaxial lesion demonstrating this subcutaneous malignant fibrous histiocytoma. This heterogeneous lesion, which is demonstrating post contrast patchy intensity along the deeper parts of the lesion. Here, we can see on these coronal images through the lower leg, T1 non-fat suppressed low hypointense lesion where in T2, it's very hyperintense with surrounding inciting edema, malignant fibrous histiocytoma. Moving on to epithelioid angiosarcomas, these are malignant vascular tumors that occur in adolescents and young adults ages 10 to 40 years of age. There is a male gender predominance. When superficially located, epithelioid angiosarcoma presents as firm, slowly growing painless nodules or plaque like lesions. Ulceration of the skin may occur and deep seated lesions tend to spread along the fascia and nerve or tendon sheath. There is a high rate of local recurrence as much as one to two thirds depending on the adequacy of initial excision.

[08:02]

Metastases occur in about 40% of patients and the 5 to 10 year survival rate is between 50% and 80%. Here, we see representative images of this epithelioid angiosarcomas. In A along the long axis of the foot, we can see this lobulated lesion where as in B we can see on T1 weighted image, it's basically isointense to skeletal muscle. Same thing can be seen in C on sagittal image where it's hyperintense on T2 weighted imaging. And here is another lesion identified in this transaxial T1 post contrast image demonstrating enhancement in epithelioid angiosarcoma. Clear cell sarcoma or malignant melanoma, these are also tumor of young adults aged 10 to 50 years of age with a peak incidence in the third and fourth decades. Approximately, 90% occur in the extremities and about 40% in the foot and ankle. The presentation is a slowly growing mass usually small with pain and tenderness in up to 50% of the cases. These are usually deep seated and often attached to aponeurosis and tendons. The tumor may extend into the subcutaneous or lower dermis but the epidermis is typically intact. And here we can see on the sagittal image of this heterogeneous lobulated lesion demonstrating elevated T2 signal intensity in this patient with malignant melanoma at the level of the ankle. Further clear cell sarcoma or malignant melanoma on MRI may be well-defined when it's small with benign-looking appearance with slightly increased intensity on T1 weighted images compared to muscle in about half of the cases.

[10:12]

They become less distinct as they enlarge along other soft tissue structures. On T1 weighted imaging, they have low signal but are slightly brighter than muscle. The T2 will be bright and enhanced with contrast. The prognosis is poor and local recurrence and metastases are common even 10 years after diagnosis. The mortality rate is 37% to 59% in these patients with clear cell sarcoma and malignant melanoma. And we can see here on this transaxial image demonstrating highly irregular less distinct enlarging mass that's infiltrating along the tendon sheath. Now, moving on to cystic tumor-like lesions, these will be the categories of ganglion cyst, synovial cyst and bursal lesions. To begin, synovial and ganglion cyst, most of these lesions synovial and ganglia are in the extremities. They are asymptomatic and incidental. The more simple appearance of the fluid, the more easier they are to aspirate and on MRI we demonstrate high T2 signal intensity, which correlates with more effective drainage and lysis. On ultrasound, we may see anechoic simple fluid is more amenable to percutaneous interventions than is heterogeneous thickened fluid. What we are looking for an ultrasound can be seen here on the right.

[12:02]

We can have an anechoic or hypoechoic lesion with a thin wall demonstrating posterior acoustic enhancement, which is seen as increased signal in the lesion dorsally. Now, synovial and ganglion cysts might be differentiated histologically but in real practice, they often are interchangeable in their terms. Synovial cyst represents joint diverticula or out-pouching lined with synovium where ganglion cysts have no true synovial lining. There is giant cell myxoid degeneration of the connective tissue and it's usually associated with disease of joint capsules and tendon sheaths. Ganglion cyst, degenerative cyst arise from the tendon sheath joint capsular bursae. Synovial cysts are attached to the underlying joint capsule or tendon sheath. Synovial cysts are intraarticular and they may recur. Most synovial cysts and ganglion cysts in the extremities are asymptomatic and incidental. Synovial cysts are herniations of the synovial membrane through the capsule of the joint filled by synovial fluid. And here, we can see these representative images, this long axis T1 weighted image demonstrating this lobular hypointense T1 weighted signal extending from the medial Lisfranc joint. Here, we can see transaxial T2 weighted image demonstrating this lobular lesion that's dissecting between the first and second metatarsal basis. And of course on C, we can see this transaxial lesion that demonstrates no internal enhancement consistent with a benign synovial cyst.

[14:00]

Moving on to bursae, there are several normal bursae throughout the body including the intermetatarsal bursa and A and B represent examples of an intermetatarsal bursa seen at the third interspace. These often can have associated neuromas or have plantar plate issues. We are looking in the intermetatarsal region. This is enlargement of the bursa. In C and D, adventitial bursae represent internal blisters that occur at pressure points where fluid decompensates into a small bursal sac. If this were to open, this would be an ulceration that could then potentially infect the underlying structures. And then of course, we can have a retrocalcaneal bursa, which represents that space between the insertion of the Achilles tendon and Kager's fat triangle and this entity is implicated in diseases such as Haglund syndrome where you have insertional Achilles tendinitis associated with retrocalcaneal and retrotendon bursitis in patients who have an ongoing friction syndrome between the posterior calcaneal process and the Achilles tendon. Of course, in this example here we can see adventitial bursitis on this post contrast examination obtained to rule out osteomyelitis. We can see in the subcutaneous soft tissues, there is peripheral curvilinear enhancement surrounded by central low signal of non-enhancement. You are looking at neuropathic osteoarthropathy with dorsal subluxation of the mid foot relative to the talar head. You are seeing changes within the cuboid and here is your adventitial bursa seen here in its peripheral enhancement.

[16:00]

Moving on to non-cystic tumor like lesions, these are perhaps the most important and most common lesions and what's important about them is to note what they are so that we can avoid further interventions. It used to be that everyone who had Morton's neuroma had that removed and then we had injections occur. But more and more we are finding that some of these entities may be harbingers of other disease for example in Morton's neuroma, we may actually have a pseudoneuroma sign, which is something that could be implicated when we are dealing with plantar capsulitis. Of course, the presence of callus is not as simple as it looks in a patient with diabetes where callus could be seen as pressure points, which could then move on to an adventitial bursa, skin breakdown could ensue and then we would have an ulcer forming and giving it risk for osteomyelitis. We will be looking for things like tophaceous gout at least the nodules because it takes about seven years of nodular making in order to being to have bony erosion. So that will be important. At times, the first person to know that the patient has nodular changes may be discovering that the patient has rheumatoid arthritis and since there are many good medicines now available, it would be important to start those medicines early in the course of disease before joint ankylosis. People concerned for palpable lumps and bumps maybe happily surprised to find out that they have a foreign body granuloma or an epidermoid reaction and not a malignant tumor. And of course, knowledge of accessory muscles would be useful to determine patients who may claudicate from internal compartmental compression syndromes from over exertion as we exercise, and of course just the presence of accessory muscles so that we don't mistake them for other pathologies.

[18:00]

Morton's neuromas, these represent extremely common benign non-neoplastic masses that occur secondary to fibrosis and neurodegeneration surrounding the plantar digital nerve. Morton's neuromas are thought to occur secondary to chronic repetitive micro trauma with compression of the plantar digital nerve against the transverse intermetatarsal ligament. The second or third intermetatarsal space is the most common along the plantar aspect of the transverse intermetatarsal ligament and dynamic ultrasound include performing the Mulder's maneuver, which I do regularly demonstrating the transverse extent in which the Morton's neuroma may go to when we squeeze the forefoot. And here, we can see in these two transaxial MR images demonstrating T1 weighted imaging at the top and T2 weighted imaging at the bottom with fusiform, dumbbell shaped mass distending the second interspace. Note the minimal enlargement of the adjacent third interdigital nerve, which can be seen in this example and that it does not fulfill the criteria for a Morton's neuroma. It must be at least 3 mm in transverse dimension. Moving onto soft tissue callus, we can take this transaxial T1 weighted image demonstrating effacement and replacement of the plantar subcutaneous soft tissues by this low signal change. This pressure point can then be opened into an ulcer if there is enough friction and continuous rubbing without repair and you can see this example of an ulcer and this person is now at risk for osteomyelitis. We can see pressure points in other areas of the foot, of course.

[20:00]

We can see here at the lateral heel. This represents a T1 area of low signal change with some intermediate to elevated T2 signal changes and then post contrast coronal imaging demonstrating enhancement in this patient with soft tissue callus. Moving on to a foreign body granuloma, this is a fibrohistiocytic and giant cell granulomatous reaction within the soft tissues. It mimics a neoplastic process and that it can have a certain amount of inflammation around it and cause pain and mass effect. The MR imaging appearance of a foreign body granuloma can vary depending on whether there is low to intermediate signal intensity on T1 weighted images and generally intermediate to high signal intensity on T2 weighted images. The foreign body itself may or may not be apparent on MR imaging and the x-ray may demonstrate metal, glass or stone. An MRI would be excellent for metal demonstrating blooming artifact. Ultrasound is very good for wood with spatial resolution of 0.5 mm-hmm, so it's an extremely powerful tool that we use to determine the presence of foreign body granuloma. And here, we have a foreign body that's captured at the medial aspect of the hind foot. We can see the curved arrows denoting the central foreign body and the surrounding inflammatory change and erosion that's occurring on the adjacent calcaneus in this chronic foreign body reaction. And here, we can see on this coronal CT rendered slice, this foreign body identified surrounded by this inflammatory reaction in this foreign body granuloma.

[22:00]

Here is a nice recent ultrasound example of a foreign body granuloma. On ultrasound, most foreign bodies are hyperechoic and we can see this lesion surrounded by this hyperechoic, hyperintense rind with vascular hyperemia. This is a classic finding in a foreign body granuloma. The central area has no intensity, no vascularity and represents the granulomatous change within this foreign body granuloma. Moving on to gout, this is classically seen as lumpy, bumpy soft tissue masses around the joints particularly the hallux MTP joint. When we look at many x-rays, if there are subluxations, they can be lateral. The mineralization of the bone is normal. There can be calcification in soft tissue masses called tophi. These are basic uric acid balls of crystals and they are deposited in the soft tissues. The joint space is relatively preserved as this does not represent a true synovitis but can incite secondary synovitis. The erosions are generally non-aggressive and punched out with sclerotic margins. The bone production includes the overhanging edge of cortex. There may be a distribution and asymmetric polyarticular changes at the first MTP joint, the carpometacarpal joint and randomly in the fingers. Other sites include feet, ankles, knees, hands and elbows and that's what you can see here in these two examples of the gout with lumpy, bumpy soft tissue nodular masses, relative preservation of the joint spaces and no bone erosions at this time. Of course, with the progression of gout, these soft tissue nodules, which can be seen here demonstrate well-defined erosions that move against the bone.

[24:08]

What's interesting to note in gout is that erosions don't only have to be within the bare area of the bone, they can actually be intraarticular or even eccentric away from the joint space and this represents nodular tophaceous gout at the hallux MTP joint here. The MR correlation of gout we can see in that example, we see multiple low signaled tophi occupying medial to the hallux MTP joint with invasion of the bone and bone erosion. In these transaxial images, note the nodular changes and the intense subcutaneous soft tissue swelling as this person has inflammatory change surrounding the soft tissue nodular tophi of gout. Moving on to subcutaneous rheumatoid nodules, we can see these nodular changes along the Achilles myo-tendon junction with different nodules of low signal intensity on all pulse sequences in this example, which can be seen on this coronal images frontal x-ray image demonstrating multiple erosions, which identified along the metatarsal heads in this patient with rheumatoid arthritis. Rheumatoid nodules represent the most common extra-articular manifestation occurring at about 40% of patients. They are universally associated with a positive rheumatoid factor. The size of the nodules varies from 2 mm to 5 cm and they are generally firm, nontender and movable within the subcutaneous soft tissues.

[26:00]

So what is the most common accessory muscle of the ankle? The peroneus cordis is the most common accessory occurring in about 10% to 22% of patients. Of course, these four representative images can be found at a website called Radsource, which is excellent and what we can see some of the more common manifestation, you could see this accessory soleus occurring along the medial aspect -- attaching to the medial aspect of the calcaneus. We can see the accessory digitorum longus and see basically paralleling the posterior tibial tendon and posterior tibial nerve. And then you can have a peroneal calcaneal internus that also travels with tarsal tunnel and both of these may cause compressive effects on the posterior tibial nerve. Here is a nice example of an accessory soleus, which we can see where I do not expect to have muscle at the level of the ankle joint line and here we could see in this fashion that there is a muscle there. And of course, the companion MR image demonstrating this low lying soleus muscle. In summary, what we have done in this past tutorial is overview of radiologic evaluation of the most common malignant soft tissue tumors of the foot and ankle. We have reviewed the imaging features of the most common cystic tumor like masses and we reviewed imaging features of the most common non-cystic tumor-like masses. Some final thoughts with regards to soft tissue masses of the foot and ankle, I recommend always to do imaging before removing a lump and send all resected fragments to the pathology to evaluate.

[28:05]

If the swelling isn't obvious, if it's not obviously a synovial cyst or plantar fibromatosis, generally it may be indicated to perform tissue sampling. All cases that have any kind of complexity should be discussed in multidisciplinary team meetings and treatment occurring specialized sarcoma centers. Conservative treatments are difficult and lead to an increased risk of local recurrence. I thank you for your time and attention and these references are available for your review.


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