C h a p t e r 4 3
Disorders of the Skeletal System: Trauma, Infections, Neoplasms, and Childhood Disorders
1095
Benign BoneTumors
Benign bone tumors usually are limited to the confines of
the bone, have well-demarcated edges, and are surrounded
by a thin rim of sclerotic bone. The most common benign
tumors are of either fibrous or cartilaginous tissue origin.
Benign fibrous tumors of the bone are common in grow-
ing bones. They are usually asymptomatic, resolve in 2 to
3 years, and do not require treatment.
8
Common carti-
laginous tumors include chondromas and osteochondro-
mas. Giant cell tumors, which contain mononuclear and
osteoclast-type giant cells, are often classified as “interme-
diate” in nature between malignant and benign.
Chondromas are benign tumors of hyaline cartilage
that usually occur in bones of endochondral origin.
18,19
They can arise within the medullary cavity, where they
are known as
endochondromas
, or on the surface of
bone, where they are called
subperiosteal
or
juxtacor-
tical chondromas
. They are usually solitary lesions of
and are most commonly found in short tubular bones
of hands and feet. Most endochondromas are asymp-
tomatic and detected incidentally. Occasionally they are
painful and cause fractures. Treatment is usually sim-
ple observation, with surgical intervention reserved for
cases in which pain or danger of fracture is present.
An
osteochondroma,
also known as an
exostosis,
is
a benign cartilage-capped tumor that is attached to the
underlying bone by a bony stalk. It is the most com-
mon benign bone tumor, about 85% of which occur as
solitary tumors.
19
The remaining tumors are seen as part
of a multiple hereditary exostosis syndrome, which is
inherited as an autosomal dominant disorder. Solitary
exostoses are usually first diagnosed in late adolescence
or early adulthood, but multiple exostoses become
apparent in childhood. Exostoses develop only in bones
of endochondral origin, arising from the metaphysis
near the growth plate of tubular bones, especially about
the knee. Clinically, osteochondromas present as slow-
growing masses, which can be painful if they impinge
on a nerve or if the stalk is fractured. In many cases
they are discovered incidentally. In multiple hereditary
exostosis, the underlying bone may be bowed and short-
ened, reflecting an associated disturbance in epiphyseal
growth. Osteochondromas usually stop growing at the
time of growth plate closure. Malignant changes are rare,
and excision of the tumor is done only when necessary.
A
giant cell tumor,
or
osteoclastoma,
is an aggressive
tumor that often behaves like a malignant tumor, metas-
tasizing through the bloodstream and recurring locally
after excision.
19,42,43
The tumor is a mixture of mononu-
clear and multinucleated osteoclast-type giant cells. The
mononuclear cells in the tumor express RANKL, and
the giant osteoclast-like cells are believed to form via
the RANK/RANKL signaling pathway (see Chapter 42).
Giant cell tumors usually arise in people in their thir-
ties or forties.
19
The majority of tumors arise around the
knee (distal femur and proximal tibia), but virtually any
bone can be involved. The tumor begins in the metaphy-
seal region, grows into the epiphysis, and may extend
into the joint surface. Pathologic fractures are com-
mon because the tumor destroys the bone substance.
Clinically, pain may occur at the tumor site, with
gradually increasing swelling. X-ray films show destruc-
tion of the bone with expansion of the cortex. The bio-
logic unpredictability of these tumors complicates their
management. Conservative surgery such as curettage is
associated with a 40% to 60% recurrence rate; up to
4% metastasize to the lungs.
19
Malignant BoneTumors
In contrast to benign tumors, primary malignant tumors
tend to be ill defined, lack sharp borders, and extend
beyond the confines of the bone. Primary malignant bone
tumors occur in all age groups and may arise in any part
of the skeleton. However, certain types of tumors tend to
target certain age groups and anatomic sites (Fig. 43-10).
For example, most osteosarcomas occur in adolescents
and are particularly common around the knee joint.
Also, people with certain conditions such as Paget dis-
ease are at increased risk for development of bone cancer.
Osteosarcoma
Chondrosarcoma
Ewing sarcoma
Giant cell tumor
FIGURE 43-10.
Common sites of primary malignant bone
tumors (chondrosarcoma, osteosarcoma, and Ewing sarcoma)
and giant cell tumor, a locally aggressive benign tumor.
