Radiological Imaging

The initial investigation for anyone presenting with a mass in the extremity is a plain radiograph done in two planes.1-3This helps to differentiate between STS and bone tumours. Additional oblique radiographs of the bone tumours may help evaluate cortical continuity and joint involvement.

Magnetic resonance imaging (MRI) is used for local staging.1-6An MRI allows for the evaluation of tumour size, the extent (including involvement of contiguous structures), and involvement of the neurovascular bundle. For bone tumours, an additional sequence of the entire long bone is done to look for skipped intramedullary lesions. If the tumour is close to a joint, the joint should be included in the images to check for contiguous involvement. The use of gadolinium contrast is optional for initial staging scans (but is required for follow-up scans post-therapy) and is generally administered unless there is a contraindication. An MRI provides details of the anatomical structures adjacent to the tumour and detects any distortion or involvement. A computed tomography (CT) scan of the local area is generally used for problem solving to visualise calcification, periosteal bone formation, and subtle cortical erosion.2,3If the MRI is contraindicated, a CT scan (with iodinated contrast) or CT angiogram can be performed.6

If sarcoma is confirmed, staging of the disease is accomplished with a helical CT scan of thechest.1-6CT scan of the abdomen and pelvis may be considered after biopsy has been performed and metastatic disease is diagnosed. For bone sarcomas, an isotope bone scan is performed to look for metastatic disease of the bone.1-3An MRI of the whole body is a sensitive imaging technique for the detection of skeletal metastases in patients with small cell neoplasms, Ewings sarcoma, and osteosarcoma.3

Additional staging investigations may be needed for selected STS, depending on the histology results. A staging CT scan of the abdomen/pelvis may be considered for myxoid liposarcoma, angiosarcoma or epithelioid sarcoma.4,5,6Of these, myxoid liposarcoma metastasises more frequently to the mediastinal and retroperitoneal spaces than the rest. In addition, myxoid liposarcomas have a higher risk of metastasis to the spine compared to other STS and an MRI of the whole spine should be considered.4In STS with a propensity for nodal spread (such as synovial sarcoma, epithelioid sarcoma, clear cell sarcoma5,6and alveolar soft part sarcoma6), an assessment of the regional lymph nodes should be done. For alveolar soft part sarcoma and angiosarcoma, an assessment of the central nervous system should be considered as part of staging.4,5

The utility of a whole body MRI and a positron emission tomography (PET)-CT is still being evaluated for staging and treatment response for bone sarcomas. However, it is not routinely recommended.1Reports have demonstrated the utility of PET scans in the evaluation of response to chemotherapy in patients with osteosarcoma, Ewings sarcoma, and advanced chordoma.3Research is ongoing.

Although a PET-CT is not recommended for routine staging6, it may be useful for prognostication, grading, and determining a patients response to chemotherapy for firm, deep lesions larger than 3 cm in high grade extremity STS.4Tumour SUVmax has been shown to correlate with tumour grade and prognostication and was an independent predictor of survival and disease progression.7Pre-treatment SUVmax and change in SUVmax after pre-operative chemotherapy independently identified patients at high risk of recurrence.8Patients with a change of SUVmax of 40% or more in response to chemotherapy were at a significantly lower risk of recurrence and death after complete resection and post-operative radiotherapy.8 PET was useful in the early assessment response to pre-operative chemotherapy and was also significantly more accurate than RECIST9in the assessment of histopathologic response to pre-operative chemotherapy.4