What is the recommended initial imaging protocol for an adult patient with a new diagnosis or suspected soft tissue sarcoma, specifically whether to request an MRI with chest CT scan or a PET CT scan?

Imaging Protocol for Soft Tissue Sarcoma

For soft tissue sarcoma, request MRI of the primary site plus chest CT scan—this is the standard imaging protocol, not PET-CT. 1

Primary Tumor Imaging

MRI is the preferred imaging modality for soft tissue tumors of the extremity, trunk, and pelvis because it provides the most accurate information for diagnosis and surgical/radiotherapy planning. 1

• For retroperitoneal or intra-thoracic sarcomas, CT is preferred instead of MRI as it provides complete staging information on the same scan. 1
• Plain radiographs may supplement MRI to identify bone involvement, fracture risk, or calcification. 1

Staging Imaging

Chest Imaging (Mandatory)

All patients with confirmed soft tissue sarcoma, particularly those with intermediate and high-grade tumors, require chest CT to exclude pulmonary metastases prior to definitive treatment. 1

• Soft tissue sarcomas metastasize predominantly to the lungs. 1
• Chest X-ray alone is insufficient for most patients, though it may be adequate for very low-risk subtypes (atypical lipomatous tumors, classic dermatofibrosarcoma protuberans) or frail elderly patients where small-volume disease detection wouldn't change management. 1

Abdomen and Pelvis CT

Include abdomen and pelvis in the staging CT for specific high-risk scenarios: 1

• Myxoid liposarcoma (mandatory—soft tissue metastases are more common; alternatively, whole body MRI can be considered) 1
• Leiomyosarcoma 1
• High-grade sarcomas of the lower extremities 1
• Epithelioid sarcoma, angiosarcoma, and small-cell sarcomas 1

Additional Site-Specific Imaging

Regional lymph node assessment (ultrasound or cross-sectional imaging) is indicated for subtypes with higher nodal involvement risk: synovial sarcoma, clear cell sarcoma, angiosarcoma, or epithelioid sarcoma. 1

Brain MRI should be considered for alveolar soft part sarcoma, clear cell sarcoma, and angiosarcoma due to higher incidence of brain metastases. 1

Role of PET-CT

PET-CT is NOT a routine investigation for soft tissue sarcoma staging. 1

PET-CT may be considered only in specific circumstances: 1

• Before radical surgery such as amputation for primary or recurrent disease 1
• In younger patients with Ewing sarcoma or rhabdomyosarcoma (where it is becoming standard) 1
• In neurofibromatosis type 1 to identify possible malignant peripheral nerve sheath tumors 1
• When conventional imaging is equivocal or clinical bone involvement is suspected 1

Common Pitfalls

Do not rely solely on ultrasound for diagnostic assessment—while useful for initial triage, ultrasound is highly user-dependent and requires MRI confirmation when diagnostic uncertainty exists. 1

Do not order PET-CT as routine staging—the 2025 UK guidelines and 2022 SELNET guidelines explicitly state it is not yet proven as a routine investigation, and the standard protocol of MRI plus chest CT (with selective abdomen/pelvis CT) remains the evidence-based approach. 1

Do not skip chest CT in favor of chest X-ray alone for intermediate or high-grade tumors—chest CT is mandatory to detect small-volume pulmonary metastases that would be missed on plain radiography. 1