Osteoid Osteoma
This tumor is a small circumscribed osteoblastic lesion that presents most frequently
in males in their second decade. The proximal femur (particularly, the femoral
neck) is affected nearly 30 percent of the time, followed by the tibia, other
long bones, phalanges, and spine, although any bone may be involved.
Symptoms are classic, with dull pain that is worse at night, relieved with salicylates
in most cases. If the lesion is in a vertebrae, the patient may present with
painful scoliosis; if in the appendicular skeleton, subcutaneous swelling and
a limp may be noted.
Radiographically, a lucent "nidus" surrounded by dense reactive bone
is characteristic. The lesion is generally less than 1 cm in diameter. At times,
a central ossified lesion may be present.
Grossly the nidus is red in color, with a granular texture. The nidus may be
difficult to see, but in some cases, preoperative labeling with oral tetracycline
shows fluorescence of the nidus under ultraviolet light. Histologically, haphazardly
arranged, thin osteoid trabeculae with varying degrees of mineralization comprise
the nidus. The trabeculae are lined by uniform osteoblasts and surrounded by
fibrovascular connective tissue with scattered multinucleated giant cells. The
nidus is clearly delineated from the surrounding reactive bone.
Surgical resection is the recommended treatment. CT localization, intraoperative
radiographs, and tetracycline labeling are helpful aids for ensuring removal
of the tumor.
Osteoblastoma
This tumor occurs most commonly in males in their second decade. It is less
frequent and larger in size than osteoid osteoma. The posterior spinal elements
are most frequently involved, but sporadic long bone involvement is often seen.
Long-standing pain, localized to the affected area, is the typical presenting
symptom. A painful scoliosis may be present in the setting of spinal involvement.
The radiographic appearance of osteoblastomas may be quite variable and nonspecific.
They often look like large osteoid osteomas, more than 2 centimeters in diameter;
50 percent of tumors are radiodense. Posterior spinal elements may be expanded
by the tumor.
Grossly, the tissue is hermorrhagic, reddish, and granular, with well-defined
reactive rims. Histologically, the lesion is characterized by irregularly arranged
trabeculae of osteoid and woven bone, similar to the nidus of osteoid osteoma.
However, in osteoblastoma, the trabeculae are less organized and mineralized
than osteoid osteoma and the tumor is more cellular and more vascular.
Treatment generally includes curettage and grafting. Care must obviously be
taken in treating lesions of the spine to preserve nerve roots and maintain
stability.
Malignant Tumors
Osteosarcoma
(Conventional)
Excluding multiple myeloma, osteosarcoma is the most common primary malignant
bone tumor. It is most frequent in children and adolescents, usually afflicting
those in the second decade of life. Males are slightly more affected than females,
in a ratio of approximately 1.4:1. The distal femur and proximal tibia are the
most common sites, followed by proximal humerus.
Pain and swelling of short duration are the most frequent presenting symptoms.
On examination a tender mass may be obvious due to soft tissue tumor extension.
Characteristically, these lesions have a predilection for the long bone metaphyses.
The radiographic appearance of this tumor is diagnostic in the majority of the
cases. It is usually a metaphyseal medullary lesion that often extends to the
soft tissues. The tumor shows frequent mineralization including the soft tissue
component. Trabecular and cortical bone destruction is common, the tumor frequently
poorly circumscribed, and periosteal elevation on a bed of new bone takes on
a characteristic appearance, known as the Codman’s triangle. Rarely, osteosarcomas
can be multicentric.
Grossly, the tumor occupies the medullary cavity, but usually has violated the
bony cortex and a soft tissue mass is present. It has a gritty consistency,
owing to its osseous components; areas of necrosis and hemorrhage account for
softer areas. Skip lesions occur in a very small percentage of cases. Histologically,
the main feature of osteosarcoma is the presence of malignant osteoid and woven
bone. The tumor cells are ovoid to spindle-shaped, with marked pleomorphism,
hyperchromatic nuclei, and mitotic figures. The tumor is generally hypercellular.
In areas containing neoplastic bone, the tumor cells in the bone are small with
minimal pleomorphism. Besides the osteoblastic component, chondroblastic and
fibroblastic components may be present.
On rare occasions, medullary osteosarcoma consists of small round cells mimicking
Ewing’s sarcoma, and is designated as small cell osteosarcoma.
Preoperative chemotherapy and tumor ablation by radical resection in the form
of amputation or limb-salvage with wide margins are the recommended treatment
options. In the event that limb salvage is a feasible option, limb reconstruction
with a custom joint prosthesis, osteochondral allograft, or resection arthrodesis
may be considered depending on the remaining bone stock and patient needs. Limb
salvage is not an option in the setting of neurovascular involvement, pathologic
fractures, infection, or extensive soft tissue involvement. Preoperative chemotherapy
may cause up to 100 percent tumor necrosis as demonstrated by histologic examination
of the resected specimen, enhancing survival and improving the outcome after
limb-sparing surgery. The 5-year survival rate is more than 50 percent, particularly
in patients who have at least 90 percent of histologic evidence of tumor necrosis.
Unfortunately, even in the most responsive tumors, recurrence after limb salvage
is approximately 6 percent.
Osteosarcoma can occur secondary to pre-existing bone disorders such as Paget’s
disease, bone infarct, and irradiated bone. The patients are usually older than
50 years and the prognosis in general is worse than primary osteosarcoma.
Telangiectatic
Osteosarcoma
It is a rare variant of osteosarcoma, accounting for less than 5 percent of
all osteosarcomas. This tumor has a similar age and site predilection as the
conventional osteosarcoma, and often presents in a similar fashion. Unlike the
former, this tumor is purely lytic, with considerable medullary and cortical
bone destruction and ill-defined margins. Lesional tissue is hemorrhagic with
extension blood clot. Histologically, osteoid production is limited and focal.
Blood-filled sinuses and multinucleated giant cells give this an appearance
that may be confused with an aneurysmal bone cyst; however, malignant pleomorphic
cells are seen within the cellular septa and cystic walls. Treatment is like
that for conventional osteosarcomas. The use of preoperative chemotherapy has
substantially improved the prognosis of this tumor, which now is similar to
conventional osteosarcoma.
Low-Grade
Central Osteosarcoma
This rare tumor has been identified in recent years and accounts for 1 to 2
percent of all osteosarcomas. Unlike the above-mentioned osteosarcomas, this
tumor typically is not associated with swelling or focal signs other than pain.
Radiographically and histologically, it is frequently difficult to determine
whether the tumor is benign or malignant. These are medullary lesions, tend
to be large and sclerotic, and often extend to the bone ends.
While the tumor is usually confined to the intramedullary cavity, focal areas
of cortical disruption may be seen without local soft tissue invasion. Grossly,
these lesions tend to be gritty. Histologically, these tumors are often indistinguishable
from parosteal osteosarcoma, as the bone trabecula are well organized and the
spindle cells show little pleomorphism, mitotic activity, or anaplasia. Other
cases resemble fibrous dysplasia.
Treatment should include wide surgical resection. Adequate surgical margin is
associated with a less than 10 percent recurrence rate. Because it is difficult
to distinguish from fibrous dysplasia, these tumors are frequently treated inadequately,
accounting for multiple recurrences and biopsies. Following recurrence, some
of these tumors may transform into high-grade osteosarcoma.
Surface Bone Forming
Tumors
Parosteal
Osteosarcoma
This tumor arises from the external surface of a bone, occurs most commonly
in the third decade of life, and involves the distal posterior femur in approximately
70 percent of cases. It usually presents as a painless mass behind the knee
and is frequently present for several years. Radiographically, these are lobulated
radiodense lesions with broad-based origins off the metaphyseal cortex and have
no continuity with the medullary cavity. Larger tumors may encircle the bone.
Microscopically, it is a low-grade malignant tumor. Osteoid and woven trabeculae
are separated by intervening fibroblastic stroma with minimal cytologic atypia.
The bony trabeculae may undergo lamellar transformation and appear like normal
bone. A cartilaginous cap may be present, giving it the appearance of an osteochondroma.
Wide surgical resection provides good local control. The prognosis is excellent,
with a 5-year survival rate of more than 80 percent, and metastases are rare.
Neither adjuvant chemotherapy or radiotherapy are necessary for the typical
lesions; however, for the more rare aggressive variant, the so-called dedifferentiated
parosteal osteosarcoma, multi-agent adjuvant chemotherapy is an important component
of treatment.
Periosteal
Osteosarcoma
This neoplasm has a peak incidence in the second decade, occurring most commonly
on the diaphysis of the tibia and femur. It generally presents as a painful
mass. Radiographically, it is characterized as an ill-defined diaphyseal surface
lesion with variable matrix mineralization, with a "scooped-out" appearance.
Perpendicular spicules of bone may be seen (creating a characteristic "sunburst"
appearance), as well as periosteal reaction and a Codman’s triangle. Usually,
no marrow involvement is present.
Histologically, these tumors show a predominant cartilaginous component with
neoplastic osteoid production. The tumor is lobulated, with peripheral condensations
of spindle cells that gives it a well-circumscribed appearance. The malignant
chondroid and osteoid cells show a moderate degree of differentiation. Treatment
involves wide surgical resection, with neoadjuvant chemotherapy.
Of the surface tumors, periosteal osteosarcoma shows intermediate degree of
malignancy between the low-grade malignant parosteal osteosarcoma and high-grade
surface osteosarcoma.
High-Grade
Surface Osteosarcoma
This rare tumor seems to peak in the second decade. It generally presents as
a painful mass; the skin may be warm and erythematous. It is highly aggressive.
Radiographically, it is marked by a poorly defined surface origin on long bones
(usually the femur), cortical destruction, and reactive bone formation. There
is no significant intramedullary involvement. Histologically, it looks like
conventional osteosarcoma, with marked cellular and nuclear pleomorphism and
anaplasia with brisk mitotic activity. Lacelike osteoid and neoplastic production
is identifiable, with varying degrees of chondroid and spindle cell formation.
Treatment is similar to conventional osteosarcoma, with wide surgical resection
or amputation and adjuvant chemotherapy.
