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Imaging in Classic Osteosarcoma

Practice Essentials

Osteosarcoma is the most common primary malignant tumor of bone, excluding plasma cell myeloma. High-grade intramedullary osteosarcoma is the classic, or conventional, form accounting for approximately 80% of all lesions.
Osteosarcoma may affect any bone but most frequently occurs in the metaphyseal areas of the distal femur and proximal tibia. Osteosarcoma spreads hematogenously, with metastasis to the lung being most common.
It is treated by a combination of surgical excision and chemotherapy.

For patients with classic osteosarcoma, radiography is almost always the initial imaging modality. Once the diagnosis is suspected, magnetic resonance imaging (MRI) is essential to determine the distribution of the tumor within the bone and the extent of any associated soft tissue mass. Computed tomography (CT) scanning is less sensitive than MRI in local evaluation of the tumor, but it is used in the staging of pulmonary metastases.

Ultrasonography is not routinely used in the staging of classic osteosarcoma lesions. The modality may be useful in guiding percutaneous biopsy. In patients treated with prosthetic implants, sonography may be the only imaging modality that can depict early local recurrence, because of the artifact produced by the metal on CT scans or MRIs.

Histologic confirmation of the nature of the tumor is required initially and should be performed only after baseline MRI studies are made.

The radiologic characteristics of osteosarcoma are demonstrated in the images below.

Radiograph of the femur in a patient with osteosar

Radiograph of the femur in a patient with osteosarcoma shows a typical Codman triangle (arrow) and more diffuse, mineralized osteoid within the soft tissues adjacent to the bone.

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Coronal T1-weighted MRI. Note the abnormal signal

Coronal T1-weighted MRI. Note the abnormal signal intensity in the metaphyseal marrow and the soft tissue mass (black arrow). Early tumor extension is shown beyond the growth plate into the epiphysis (white arrows).

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Guidelines

The National Comprehensive Cancer Network (NCCN) guidelines recommend that the initial workup include imaging of the primary site by MRI with or without CT scanning and chest imaging, including chest CT and head-to-toe PET/CT scan and/or bone scan. More detailed imaging of abnormalities identified on primary imaging by CT or MRI is required when metastatic disease is suspected. Repeat imaging using pretreatment imaging modalities should be performed following chemotherapy to reassess the tumor for resectability.

The Europen Society of Medical Oncology (ESMO) guidelines recommend radiography for the initial evaluation of osteosarcoma. When the diagnosis of malignancy cannot be excluded with certainty on radiographs, then MRI of the whole compartment with adjacent joints should be performed, according to ESMO. CT should be used only in the case of diagnostic problems or doubt, to visualise more clearly calcification, periosteal bone formation, or cortical destruction. For disease staging, ESMO recommends bone scintigraphy, chest radiographs, and CT to assess the extent of distant disease.

Surveillance

Because of the potential for development of local recurrence and distant metastasis after resection of a primary bone malignancy, ongoing surveillance is considered an essential aspect of osteosarcoma management. However, minimal data exist regarding the incidence and timing of these events.

Once treatment is completed, the NCCN guidelines recommend surveillance every 3 months for 2 years, every 4 months for year 3, every 6 months for years 4 and 5, and annually thereafter.  Surveillance includes chest imaging and imaging of the primary site as performed during the initial evaluation. Head-to-toe PET/CT and/or bone scan may also be considered.
 

ESMO guidelines recommend surveillance with imaging of the local site and chest x-ray/CT but does not give strict timelines in the absence of  formal validation. Follow-up intervals after the completion of chemotherapy are suggested every 2–3 months for the first 2 years; every 2–4 months for years 3–4; every 6 months for years 5–10, and thereafter every 6–12 months
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