MSK: Soft Tissue Masses Flashcards
What are the salient soft tissue masses?
- Malignant fibrous histiocytoma (AKA pleomorphic undifferentiated sarcoma)
- Synovial sarcoma
- Lipoma/atypical lipoma/liposarcoma
- Hemangioma
- Myxoma
What is the most common location for a pleomorphic undifferentiated sarcoma?
Proximal extremities (the thigh is the most common)
Pleomorphic undifferentiated sarcoma is most commonly seen in what pt population?
Older pts
Elderly female develops a thigh muscle hematoma after standing up from a chair…
Think pleomorphic undifferentiated sarcoma (these have a high risk of hemorrhage)
Classic imaging feature of pleomorphic undifferentiated sarcoma
Soft tissue mass that is often T2 dark/intermediate (most soft tissue masses are T2 bright)
Note: This used to be called a malignant fibrous histiocytoma (fibrous should make you think dark on MRI).
Bone infarctions can undergo malignant transformation to…
Pleomorphic undifferentiated sarcoma (AKA sarcomatous transformation)
Risk factors for pleomorphic undifferentiated sarcoma
- Old age
- Prior radiation
Synovial sarcoma is most common in what pt population?
Ages 20-40
What is the most common location for synovial sarcoma?
Peripheral lower extremities (close to a joint, but not in the joint)
Complex appearance of a Bakers cyst with internal flow on color Doppler…
Think synovial sarcoma
Popliteal fossa cyst that is not located between the semimembranosus tendon and medial head of gastrocnemius…
Not a Bakers cyst, be suspicious for synovial sarcoma and recommend an MRI
Synovial sarcoma
Note: “Triple sign” on T2 image (mass contains T2 high, intermediate, and low signal).
Think synovial sarcoma
Note: “Bowl of grapes sign” (multiple fluid-fluid levels in a soft tissue mass).
Irregular soft tissue calcifications near a joint, think synovial sarcoma
Soft tissue calcifications with adjacent bone erosions…
Think synovial sarcoma
Note: Most soft tissue sarcomas don’t cause bone erosions but synovial sarcomas can.
Clinical presentation of synovial sarcoma
Painful soft tissue mass
Note: Most other sarcomas are painless.
90% of synovial sarcomas have what genetic abnormality?
Translocation of X-18
What is the most common malignancy in teenagers to involve the foot/ankle/lower extremity?
Synovial sarcoma
Are synovial sarcomas fast growing?
No, they are usually slow growing (which can make radiologists mistake them for a benign lesion)
Ball-like tumor in the extremity of a young adult…
Think synovial sarcoma
Soft tissue tumor in the foot of a young adult…
Think synovial sarcoma
Think retroperitoneal liposarcoma
Imaging features that should make you suspicious for liposarcoma rather than a simple lipoma
- Thick, nodular septations
- Minimal fat content
- Enhancing components
Note: Liposarcomas also tend to be deeper (e.g. retroperitoneal) rather than superficial.
What is the most common subtype of liposarcoma in pts under age 20?
Myxoid liposarcoma
Note: These are tricky because they usually appear dark on T1 and bright on T2 (and can be confused for a cyst). If you aren’t completely sure its a cyst, get post contrast imaging.
Think soft tissue venous malformation
6 m/o
Think infantile hemangioma
Think hemangioma
Note: Phleboliths on radiography and flow voids and macroscopic fat in a soft tissue mass on MRI.
Do sot tissue hemangiomas respect fascial boundaries?
No, they will infiltrate through fascial boundaries (a somewhat unique feature for a soft tissue mass)
Polyostotic fibrous dysplasia and multiple soft tissue myxomas…
Mazabraud syndrome (rare)
Next step: MRI demonstrates an avidly-enhancing soft tissue mass with flow voids…
Get radiographs (to look for phleboliths, which would be consistent with a soft tissue hemangioma/vascular malformation)
Think myxoma
Note: Soft tissue mass that is T1 dark relative to muscle, T2 bright,and peripherally or heterogeneously enhancing.
Think Mazabraud syndrome (polyostotic fibrous dysplasia and multiple soft tissue myxomas)
Treatment for osteosarcoma
Neoadjuvant chemotherapy (to kill micro metastases), followed by wide excision
Treatment for Ewings sarcoms
Neoadjuvant chemotherapy and radiation, followed by wide excision
Treatment for chondrosarcoma
Usually just wide local excision
Treatment for giant cell tumor
Usually excision with arthroplasty (because these extend to the articular surface)
Pigmented villonodular synovitis
An uncommon benign neoplastic process that results in synovial proliferation and hemosiderin deposition
What is the most common location for pigmented villonodular synovitis?
The knee (65-80%)
Radiographic findings seen in pigmented villonodular synovitis
- Joint effusion
- +/- marginal erosions (with preservation of the joint space)
Note: It is not possible to distinguish pigmented villonodular synovitis from synovial chondromatosis on radiography alone.
GRE
Pigmented villonodular synovitis
Note: Blooming artifact from hemosiderin deposition on GRE.
Treatment for pigmented villonodular synovitis
Complete synovectomy
Note: Recurrence is common (20-50%).
Pigmented villonodular synovitis is unusual in pediatric pts, but when it occurs it is usually…
Polyarticular
What are the major types of synovial chondromatosis?
- Primary
- Secondary (due to degenerative changes)
Pathophysiology of primary synovial chondromatosis
Primary synovial chondromatosis is a neoplastic precess resulting in the formation of multiple cartilaginous nodules in the synovium of joints, tendon sheaths or bursae. These nodules then progress to loose bodies.
What is the most common location for primary synovial chondromatosis?
The knee (70%)
Primary synovial condromatosis is most common in what age group?
40s-50s
What is the characteristic appearance of intraarticular loose bodies in primary synovial chondromatosis?
Numerous, uniformly sized loose bodies +/- chondroid calcification
Primary synovial chondromatosis
Treatment for primary synovial chondromatosis
Removal of intraarticular loose bodies +/- synovectomy
Primary synovial chondromatosis
Is pigmented villonodular synovitis or primary synovial chondromatosis associated with hemarthrosis?
Pigmented villonodular synovitis (this is why there is hemosiderin deposition in PVNS)
Which often calcifies: pigmented villonodular synovitis or synovial chondromatosis?
Synovial chondromatosis
Note: PVNS never calcifies.
Think secondary synovial chondromatosis
Note: This usually has fewer and larger intraarticular loose bodies.
What is the most common location for diabetic myonecrosis?
- Thigh (80%)
- Calf (20%)
Poorly-controlled type 1 diabetic
Diabetic myonecrosis
Note: Do NOT biopsy this (delays recovery time and has a high complication rate).
Lipoma arborescens
Note: “Frond-like” deposition of fatty tissue in the synovial lining of joints/bursa.
Lipoma arborescens is most common in what age group?
50s-70s
What is the most common location for lipoma arborescens?
The suprapatellar bursa of the knee
Risk factors for lipoma arborescens
- Prior trauma
- Osteoarthritis
- Rheumatoid arthritis
Lipoma arborescens
Note: “Frond-like” deposition of fatty tissue in the synovial lining of joints/bursa. It behaves like fat (responds to fat saturation).
Knee joint ultrasound
Lipoma arborescens
Note: “Frond-like” deposition of fatty tissue in the synovial lining of joints/bursa.
Think tumoral calcinosis
Note: Big, lobular calcium near a joint.
Think tumoral calcinosis
Note: Big, lobular/cystic calcium deposits near a joint with fluid-calcium levels (arrows).
What is the most common location for tumoral calcinosis?
Greater trochanteric bursa
Note: Hips, elbows, and shoulders are common. Knee is rare (helps distinguish from synovial chondromatosis).
Pathophysiology of tumoral calcinosis
Hereditary phosphate metabolism issue (calcium levels are normal, but phosphate levels are usually abnormal)
Think metastatic calcification
Note: Seen in pts with hypercalcemis (e.g. renal failure or hyperparathyroidism).
Which features should make you think metastatic calcification rather than tumoral calcification?
- Presence of renal and lung calcifications
- Hypercalcemia (tumoral calcinosis will have normal calcium levels)
Note: If you see fluid-calcium levels, think tumoral calcinosis.
Think myositis ossificans
Note: Circumferential calcifications with a Lucent center. Do NOT biopsy. This can look scary on MRI if imaged during early phases (due to edema and avid enhancement).
Cortical desmoid
Note: This is not actually a desmoid, but a tug lesion from the medial gastrocnemius and ADDuctor magnus.
Synovial herniation pit (do not touch lesion)
Note: Characteristic location in the anterosuperior femoral neck. This likely has an association with femoroacetabular impingement.
Osteoid osteoma
Note: This was originally mistaken for a synovial herniation pit on MRI.
Synovial herniation pit
Special considerations when performing a pelvic bone biopsy
Avoid crossing the gluteal muscles (which may be needed for reconstruction)
Special considerations when performing a knee bone biopsy
- Avoid the joint space (including communicating bursa, such as the supra patellar bursa)
- Avoid crossing the quadriceps tendon
Special considerations when performing a shoulder bone biopsy
Avoid the posterior 2/3 (the axillary nerve runs posterior to anterior, so a posterior resection will denervate the anterior 1/3)
