Bone Tumors

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It is important to distinguish between tumours of bone and tumours in bone, since the most commonly seen tumours in bone are blood-borne metastases from other primary sites, and tumours of haemopoietic cells located within the marrow spaces of bones, particularly myeloma. 
 
Primary tumours derived from the cells involved in bone formation and modelling are comparatively rare, the most common lesions being osteosarcoma and chondrosarcoma.
Less common primary tumours of bone are summarized in Some intraosseous lesions with the appearance of bone tumours are not true neoplasms, but represent hamartomatous malformations, non-neoplastic proliferative disorders, or non-neoplastic cysts.
 
The most common malignant primary tumours of bone are osteosarcomas and chondrosarcomas
 
Osteosarcoma is a malignant tumour of osteoblasts, which occurs in adolescent children, most commonly in boys.
The majority arise around the knee, either in the lower end of the femur or in the upper end of the tibia, although a small percentage occur in other long bones such as the humerus, or in the upper end of the femur.
 
The tumour causes gradually increasing pain around the knee, and is often well-advanced at the time of clinical and radiological diagnosis.
The tumour originates in the medullary cavity close to the metaphyseal plate and spreads extensively within the medullary cavity, eventually eroding through cortical plate and extending into soft tissue.
The malignant osteoblasts produce varying amounts of osteoid collagen, some of which becomes mineralized; this mineralization in the tumour can be demonstrated radiologically and by other imaging methods, and is particularly apparent when the tumour is invading soft tissues. 
 
Osteosarcoma in adults is largely confined to elderly patients with a long history of active Paget's disease of bone, the tumour occasionally developing in an area of Paget's disease.
 
Chondrosarcoma mainly occurs in adults, usually the middle-aged or elderly, and is particularly common in the bones of the pelvis.
Chondrosarcomas are slow-growing tumours that often reach a large size, expanding the bone and eventually breaking through the periosteum into surrounding soft tissue, but usually maintaining a clearly defined border. Although malignant, they metastasize very late in most cases, the majority being low-grade well-differentiated tumours, histologically very similar to benign cartilaginous tumours; a few are high-grade poorly differentiated tumours with marked pleomorphism and high mitotic activity; they grow rapidly with early blood-borne metastases.
 
Macroscopically, tumours have a glistening white appearance.
Radical local surgery may be curative in the low-grade group. 
 
The most common benign bone-forming tumour is osteoid osteoma
 
Osteoid osteomas are mainly found in the long bones of the lower leg, arising in adolescents and young adults.
They present with bone pain localized to the area of the lesion.
Usually less than 2 cm in diameter, they are radiologically characteristic, with a central dense area surrounded by a halo of bone lucency.
Histologically they are composed of active osteoblasts, which deposit large irregular masses of osteoid collagen in a haphazard manner.
 
So-called giant osteoid osteoma or benign osteoblastoma is a larger tumour with similar histological features, mainly affecting the bones of the hands and feet and vertebrae; these are often more cellular than small osteoid osteomas, more locally aggressive, and can recur after incomplete excision.
 
Ivory osteoma is composed of densely compact bone of cortical type with Haversian systems. It arises as small round nodules, usually in the skull bones.
 
The most common benign tumour of cartilage-forming tissue is the chondroma
 
Chondromas, most commonly found in the small bones of the hands and feet, may be single (solitary enchondroma) or multiple (enchondromatosis).
The tumours arise in the metaphysis and may originate from residual nests of cartilage cells left behind as bone growth proceeds.
They are composed of cartilaginous matrix containing scattered benign chondrocytes.
A solitary chondroma at the periphery rarely undergoes malignant change, but this occasionally happens in multiple enchondromatosis.
The term 'enchondroma' is used to indicate that these tumours arise within the bone, to distinguish them from the benign osteochondroma, which grows as a nodular exophytic lesion.
 
Benign osteochondroma grows as an exophytic nodule from the metaphysis of a long bone
 
Benign osteochondromas, also known as cartilage-capped exostoses, may be solitary (as a sporadic abnormality in childhood and adolescence) or multiple (as in the autosomal dominant condition hereditary multiple exostoses).
They are composed of a nodule of protuberant bone covered by a cap of cartilage and an outer layer of perichondrium. In children the cartilage layer may be thick, but this thins as the patient ages. Lesions are found most commonly in the humerus, femur and upper end of the tibia. Chondrosarcomatous change is rare in single sporadic lesions, but is more common in hereditary multiple lesions.
 
Giant-cell tumour of bone, sometimes called osteoclastoma, arises in the epiphysis of a long bone
 
Giant-cell tumours of bone are osteolytic lesions that occur in young and middle-aged adults, generally being more common in women.
The bone is replaced by a mass of large multinucleated giant cells resembling large osteoclasts, which are embedded in a supporting spindle-celled stroma.
The lesions expand into the metaphysis and, with enlargement, may erode the cortical bone. However, they rarely penetrate the periosteum or articular cartilage.
These locally aggressive tumours are difficult to treat because of frequent recurrence at the site of inadequate local excision, particularly if an attempt has been made to eradicate the tumour by curettage.
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