Osteosarcoma is the most common primary malignant tumor of bone, excluding plasma cell myeloma. Approximately 75% of all osteosarcomas are of the classic or conventional type, and the remaining 25% comprise the osteosarcoma variants, which are the subject of this article. The variants are a heterogeneous group of osteosarcomas with a range of different imaging and behavioral features.
Preferred modalities for evaluating primary disease are radiography, MRI, and sometimes computed tomography (CT) scanning. Staging is always performed by using chest CT scanning to detect pulmonary metastases. Isotopic bone scanning is generally used to detect skeletal metastases or synchronous tumors, but whole-body MRI may replace this study.
The overall prognosis for patients with osteosarcoma depends on the stage of the tumor at presentation. Without metastases, long-term survival is in the order of 60-85%.
Telangiectatic osteosarcoma (as shown in the images below) has been considered more aggressive than classic osteosarcoma, but studies of long-term survival after optimum treatment now indicate that the aggressiveness of telangiectatic osteosarcoma is similar to that of the classic type.
Frontal radiograph of the distal femur in a patient with telangiectatic osteosarcoma. The radiograph shows mixed medullary sclerosis and lucency, cortical destruction medially, aggressive periosteal changes, and a large soft-tissue mass with peripheral ossification.
Coronal short-tau inversion recovery (STIR) magnetic resonance imaging (MRI) scan of the same patient (patient with telangiectatic osteosarcoma). Note the abnormal signal intensity of the bone marrow in the metaphysis of the femur, the cortical destruction, and the prominent soft-tissue mass with the surrounding edema or reactive zone.
Axial T2-weighted magnetic resonance imaging (MRI) scan of the same patient (patient with telangiectatic osteosarcoma). A fluid-fluid level is present within the abnormal extraosseous tumor mass (arrow). The abnormal intramedullary tissue is less obvious in this sequence than in others.
Intraosseous low-grade osteosarcoma generally has a good prognosis. Gnathic osteosarcoma (as shown in the images below) is less frequently associated with metastatic spread than is conventional osteosarcoma, but local disease recurrence is often problematic.
Frontal radiograph of the mandible in an adult with gnathic osteosarcoma. The radiograph shows a large, expansile lesion in the right ramus (arrow), with a mixed lytic and sclerotic appearance.
Axial computed tomography (CT) scan obtained with bone window settings, in the same patient (adult with gnathic osteosarcoma). Osseous expansion and the mixed lytic and sclerotic process are again appreciated. A large soft-tissue component (arrow) also is now visible.
Axial computed tomography (CT) scan obtained with soft-tissue window settings, in the same patient (adult with gnathic osteosarcoma). Extension of ossified matrix into the soft-tissue component of the tumor is shown (arrow).
The prognosis for intracortical osteosarcoma is unclear because of its rarity. Both small-cell and secondary osteosarcoma are generally associated with a poor prognosis.
High-grade surface osteosarcoma has a prognosis similar to that for a conventional osteosarcoma, and the prognosis for periosteal osteosarcoma (shown in the images below) is better than that for conventional osteosarcoma.
Anteroposterior (AP) radiograph of the proximal tibia in a child with periosteal osteosarcoma. The metal pointer localizes the lesion for biopsy.
Coronal short-tau inversion recovery (STIR) magnetic resonance imaging (MRI) scan of the same patient (child with periosteal osteosarcoma). The ossified component of the tumor shows low signal intensity (white arrow), but superficially, hyperintense material (black arrow) is present. This may be chondroblastic soft-tissue extension of tumor, adjacent reactive edema, or a combination of both.
The prognosis for a parosteal osteosarcoma (as shown in the images below) is generally excellent.
Lateral radiograph of the proximal tibia in a patient with parosteal osteosarcoma. Note the opaque, lobulated, amorphous or cloudlike mass of abnormal, ossified tumor, which is inseparable from the posterior aspect of the tibia.
Axial computed tomography (CT) scan of the same patient (patient with parosteal osteosarcoma). The ossified tumor mass is readily shown, and the thickened cortex is visible at the junction of tumor and normal bone (arrow). The medullary cavity of the tibia appears normal.
Axial T1-weighted magnetic resonance imaging (MRI) scan of the same patient (patient with parosteal osteosarcoma). The medullary cavity of the tibia shows predominantly normal signal intensity, except posteriorly, where the slightly reduced signal intensity raises the possibility of early tumoral invasion (arrow). This area was normal on histologic examination.
The prognosis for multicentric osteosarcoma is dire.
Conventional osteosarcoma is most frequent in areas of high skeletal growth, especially the metaphyseal regions of the distal femur, proximal tibia, and proximal humerus. Most osteosarcoma variants follow a similar distribution, with the exception of gnathic (mandible and maxilla) lesions, intracortical lesions (rare but more typically diaphyseal), periosteal lesions (more typically diaphyseal), and secondary osteosarcomas.
The last osteosarcomas frequently occur in the pelvis and proximal femur, often in association with Paget disease (as demonstrated in the images below).
Anteroposterior (AP) radiograph of the proximal femur in a patient with Paget disease demonstrates the typical features of cortical thickening, osseous expansion, and trabecular coarsening. In addition, irregular bone lucency and cortical destruction are shown in the medial aspect of the shaft; this is consistent with secondary sarcoma formation.
Localized isotopic bone scan in the same patient (patient with Paget disease) shows a large area of reduced uptake in the medial side of the proximal femoral shaft at the site of the secondary sarcoma (arrow).
Coronal T1-weighted magnetic resonance imaging (MRI) scan of the same patient (patient with Paget disease). The tumor is shown in the proximal shaft of the right femur (white arrow), with cortical destruction and a large soft-tissue component (black arrow).