Musculoskeletal ImagingChondrosarcoma
a
malignant tumour derived from the
cartilage cell line but without direct osteoid formation. Various types of chondrosarcomas are described on the basis of location within bone (central, peripheral, juxtacortical), occurrence as a primary or secondary
tumour, degree of cellular differentiation and other features (clear cell, mesenchymal and dedifferentiated chondrosarcomas). The tumours are composed of lobules of
cartilage, with the less aggressive forms showing areas of
calcification and degeneration.
Conventional chondrosarcomas
can be categorized as central chondrosarcomas (arising within the medullary cavity, either
de novo or in a pre-existing enchondroma) or peripheral chondrosarcomas (arising near the surface of the bone). Presenting features include pain and a soft tissue mass. Most common sites of involvement are the long
tubular bones, especially the femur, innominate bone, ribs,
vertebrae, scapula and sternum. Four grades are recognized on the basis of differentiation and aggressiveness.
Radiographic features of central and peripheral chondrosarcomas may vary depending on circumstances, such as presence or absence of tumoural calcification, patterns of bone destruction, encroachment on the cortex and presence of periostitis (Fig.1) (Fig.2). High grade (aggressive) chondrosarcomas may show large areas of irregular or absent calcification of the tumour and a poorly defined boundary between normal and abnormal bone.
Bone scans show increased uptake of radionuclide in cases of central chondrosarcomas and reveal metabolically active areas in peripheral chondrosarcomas. Absence of uptake essentially rules out malignant tranformation of an ostechondroma.
CT scanning is valuable in showing the extent of the tumour and may be able to define the thickness of the cartilage cap in peripheral chondrosarcomas.
MR imaging defines the full extent of tumour and is particularly useful in anatomically complex areas. Lesions are of inhomogeneous or homogeneous high signal intensity on T2-weighted spin-echo images. Administration of gadolinium compounds allows focal or diffuse enhancement of signal intensity, although calcification is detected more easily with CT scanning.
Central chondrosarcomas typically appear on radiographs as elongated, slightly expansile osteolytic lesions with cortical thickening, scattered calcification, endosteal bone erosion and periosteal bone formation. Soft tissue involvement may be more pronounced in flat and irregular bones than in the long tubular bones.
Peripheral chondrosarcomas
commonly arise from pre-existing osteochondromas or develop as
juxtacortical chondrosarcomas from the periosteal membrane.
Malignant transformation may be suggested by the presence of a bulky, irregular cartilaginous cap with scattered calcifications in the cartilaginous portion. Other suggestive signs are the presence of a large soft tissue mass, rapid growth, destruction or pressure erosion of adjacent bone and
focal areas of radiolucency within the interior of the osteochondroma.
Dedifferentiated chondrosarcoma
represents a locally aggressive variant of conventional chondrosarcoma of bone with poor prognosis that consists of a low-grade
malignant cartilage tumour associated with a highly anaplastic sarcoma. This
tumour has a similar distribution to other conventional chondrosarcomas but reveals motheaten bone destruction and partial
calcification. Noncalcified areas show the most aggressive bone destruction and soft tissue swelling.
Other types of chondrosarcomas
which are discussed under their specific names, are
juxtacortical chondrosarcoma,
clear cell chondrosarcoma, mesenchymal chondrosarcoma and
synovial chondrosarcoma.
DR/RB
DR/RB