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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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