Musculoskeletal Tumors Part 1
Review of musculoskeletal tumors for radiology board exams.
Show Notes/Study Guide:
What are top differential considerations for lytic/lucent bone lesions?
Two primary mnemonics are common for this
FOGMACHINES
Fibrous dysplasia/Fibrous cortical defect, Osteoblastoma, Giant cell tumor/Geode, Mets/Myeloma, Aneurysmal bone cyst, Chondromyxoid fibroma/Chondroblastoma, Hyperparathyroidism (brown tumor)/Hemangioma, Infection/Infarction, Non-ossifying fibroma, Enchondroma/Eosinophilic granuloma, Solitary (unicameral) bone cyst
FEGNOMASHIC
Fibrous dysplasia/Fibrous cortical defect, Enchondroma/Eosinophilic granuloma, Giant cell tumor/Geode, Non-ossifying fibroma, Osteoblastoma, Metastasis/Myeloma, Aneurysmal bone cyst, Solitary (unicameral) bone cyst, Hyperparathyroidism (brown tumor), Infection/Infarction of bone, Chondromyxoid fibroma/Chondroblastoma
What location is most common for enchondromas?
Hands and feet (approximately 50% of enchondromas). Note that malignancy of the fingers/toes is rare so if you see a lucent lesion in the bones of the fingers or toes enchondroma needs to be on your differential diagnosis. Enchondromas are typically intramedullary lesions. Enchondroma with pain think pathologic fracture due to enchondroma cortical weakening.
What are differential considerations for an enchondroma of the hands/feet?
Brown tumor (hyperparathyroidism), sarcoid, intraosseous ganglion, metastatic disease.
What is bizarre parosteal osteochondromatous proliferation (BPOP) aka Nora’s lesion?
Heterotopic ossification that can form mass-like lesions arising from the periosteum of the phalanges. This is an acquired exostosis meaning it is reactive and often post-traumatic in etiology. Other features include lack of cortical disruption. Common location is the proximal phalanges of the hand. Differential consideration is a juxtacortical chondroma. It is important not to confuse BPOP with a chondrosarcoma or osteosarcoma. BPOP is most common in patients under 30 years old. BPOP shows cortical continuity with the lesion with lack of medullary involvement. BPOP is a benign lesion that may be locally aggressive and recurrent following excision but is thought to have no risk of distant metastatic disease.
Chondrosarcomas may be secondary to what lesions?
Enchondromas and osteochondromas may degenerate into a chondrosarcoma. Note that primary chondrosarcomas are also possible. Chondrosarcomas commonly involve the pelvis, femur and humerus. Characteristic features include a lobular growth pattern with high T2 signal due to high water content and cartilaginous nodules, “rings and arcs” pattern of chondroid mineralization (best depicted by CT), endosteal scalloping, and soft tissue extension.
What may be the best feature to distinguish between an enchondroma and a chondrosarcoma?
Endosteal scalloping may be the best distinguishing feature to tell the difference between a chondrosarcoma and an enchondroma. Increased length and depth of scalloping (scalloping >2/3 of normal cortical thickness) is most suggestive for chondrosarcoma.
What are the 3 most common malignant bone tumors?
Myeloma, osteosarcoma, then chondrosarcoma.
Most chondrosarcomas are well-differentiated low-grade tumors. What are imaging findings that suggest a de-differentiated, high-grade chondrosarcoma?
A chondrosarcoma with a soft tissue mass without mineralized matrix is suggestive of a high-grade malignancy. Some have termed this a bimorphic appearance (part mineralized “arcs and whirls”, etc and part non-mineralized with soft tissue component).
What are key features of a telangiectatic osteosarcoma?
Distal femur location is most common, tumor has necrotic and hemorrhagic portions with multiple fluid-fluid levels.
What is the top differential consideration for a telangiectatic osteosarcoma?
Aneurysmal bone cyst. 2/3 of aneurysmal bone cysts are primary. Secondary aneurysmal bone cysts may arise from a giant cell tumor or chondroblastoma. Note that of the lytic lesions this is the most expansile lesion which can help differentiate an ABC from other lytic processes.
What are key features of a chondromyxoid fibroma?
A chondromyxoid fibroma is a rare eccentric lytic lesion, commonly in people under 30 years of age, with a metaphyseal location, commonly around the knee, demonstrating cortical thinning, pseudotrabeculation (septations), no periosteal reaction, and sclerotic, well-defined margins.
What is the classic location on board exams for an adamantinoma?
The tibial diaphysis is the classic location on board exams for an adamantinoma. Adamantinomas are very rare lesions that may be multicentric. These appear as eccentric lesions involving the anterior tibial cortex, much less commonly involving the fibula. These are often indolent lesions with risk of late metastases to the lungs. Classic would be the primary lesion that recurs after therapy, then shows late metastatic disease to the lungs.
True of false: synovial sarcomas arise from joints
False—synovial sarcomas arise in proximity to but not from joints. Synovial sarcomas are most common in the extremities and present as juxta-articular lesions. Classic history on a board exam would be a pediatric patient with a multi-cystic appearing mass with well-defined margins around the knee joint but can also be seen around the ankles and other joints.
What is the “triple sign” of a synovial sarcoma?
Heterogeneous signal from: solid mass, hemorrhage, and calcification.
What is the “bowl of grapes” sign of a synovial sarcoma?
Mass with a multilobular appearance with multiple cyst-like areas with diffuse blood-fluid levels.
What are imaging features suggestive of well-differentiated, de-differentiated, pleomorphic and myxoid liposarcoma?
Well-differentiated liposarcomas often show >75% fat, thickened septa (>2 mm), and soft tissue nodularity.
De-differentiated liposarcomas often have a nodular dominant focus > 1 cm in size.
Pleomorphic liposarcoma typically presents as a heterogeneous mass with dominant soft tissue components and only small fat-containing foci.
Myxoid liposarcoma often shows a classic myxoid background (T2-bright) with some nodular soft tissue and adipose tissue components.
