• A malignant cartilage-producing tumour – it generally has a better prognosis than an osteosarcoma (due to late metastases) • A major consideration is the differentiation between a chondroma and a low-grade chondrosarcoma • Slow growth: this allows reactive change with periosteal new bone + bone expansion + endosteal resorption (endosteal scalloping > ⅔ of the cortical width suggests a chondrosarcoma rather than a chondroma) • More aggressive tumours: cortical destruction • A malignant osteoid-producing tumour • It is the 2nd commonest primary malignant bone lesion after myeloma • Pain or a palpable mass (usually > 6cm at presentation) • 80% of cases present between 10 and 30 years • It is a highly vascular tumour with early haematogenous metastases to the lung (with a subpleural location, possible calcification and potential pneumothorax formation) • Synchronous: multiple osteoblastic metaphyseal lesions occurring in children or adolescents • Metachronous: this affects older patients, presenting with a solitary lytic or sclerotic lesion within a long or flat bone
Malignant bone tumours
CHONDROID ORIGIN
CHONDROSARCOMA
DEFINITION
RADIOLOGICAL FEATURES
XR
an increased cortical thickness (if the periosteal reaction outweighs the cortical scalloping)
one should consider dedifferentiation to a more malignant type
PEARLS
OSTEOSARCOMA
OSTEOSARCOMA
DEFINITION
it is commonly a primary central osteosarcoma (75%)
CLINICAL PRESENTATION
pathological fracture
there is a 2nd smaller peak occurring above the age of 40 years which is seen commonly within the flat bones and vertebrae and usually secondary to a pre-existing disorder (e.g. Paget’s disease)
PEARLS
occasionally there are lymphatic metastases
Primary multicentric osteosarcoma
it has a poor prognosis
multiple lesions are seen after more than 5 months 
this has a better prognosis than a synchronous lesion
Malignant bone tumours
Grade II: myxoid 
Grade III: high grade 
dedifferentiated: this refers to the development of an adjacent non-chondroid tumour (e.g. an osteosarcoma, fibrosarcoma, or MFH)
it can present with insidious pain, a palpable mass or a pathological fracture
it is found within the metaphysis (± epiphyseal extension)
there is a narrow zone of transition
T2WI: multilobulated high SI lesion 
matrix mineralization appears as foci of signal void 
T1WI + Gad: minimal peripheral or septal enhancement (as it is poorly vascularized)
it involves the long bones (usually the distal femoral or proximal humeral metaphyses) 
there is a good prognosis after resection
it has a very much more cellular malignant matrix than a normal chondrosarcoma
there is often chondroid calcification 
there is a predilection for the ribs and mandible
it is a low-grade tumour with a better prognosis
it has a lytic appearance (± a loculated or ‘soap bubble’ appearance)
it can cross the growth plate with epiphyseal extension seen in 75% of cases
there is a wide zone of transition 
there can be cortical destruction with an extraosseous mass and cloud-like matrix mineralization
reactive Codman’s triangles are seen at the margins of the lesion
malignant change is reported in up to 14% of cases of Paget’s disease (M:F, 2:1) 
it should be suspected if there is a change in pain or a pathological fracture 
it has a very poor prognosis
the spine is usually spared
it is usually an osteosarcoma with a mean latency period of 15 years 
it commonly occurs within the pelvis and shoulder girdle and has a poor prognosis
a > 3 year latency 
a histology different from the original tumour
it is slow growing with a good prognosis (which may dedifferentiate) 
it has an equal sex incidence
it may wrap around the bone 
satellite bony masses can be seen in the adjacent soft tissue
T2WI: high SI at the periphery may indicate higher grade or dedifferentiation
juxtacortical myositis ossificans
there is a slight male preponderance
there is rarely nodular matrix calcification
