Should an MRI with or without contrast be ordered for a patient with a 1.8cm sacrum lytic lesion?

MRI Without Contrast for Sacral Lytic Lesion

For a patient with a 1.8cm sacral lytic lesion, order MRI without contrast as the primary imaging modality. 1

Primary Recommendation

MRI without IV contrast is rated as "usually appropriate" (rating 8-9) by the American College of Radiology for evaluating sacral lesions, including suspected stress fractures and bone lesions in this anatomic location. 1 This approach provides excellent soft tissue characterization, depicts bone marrow involvement, and avoids unnecessary contrast administration in most cases.

When Contrast May Be Considered

Add IV contrast to the MRI protocol only if:

• There is specific concern for malignancy or soft-tissue mass that requires enhanced characterization (rating 5-7 as "may be appropriate"). 1
• Initial non-contrast MRI findings are indeterminate and contrast could help differentiate between benign and malignant processes. 1
• You suspect infection or abscess where contrast enhancement patterns aid diagnosis. 2

The ACR specifically notes that contrast is not routinely necessary for initial characterization of bone lesions and should be reserved for cases where it will change management. 1

Rationale for This Approach

MRI without contrast excels at detecting bone marrow abnormalities and characterizing lytic lesions through T1-weighted sequences (showing anatomic detail) and fluid-sensitive sequences like T2-weighted fat-saturated or STIR images (showing marrow edema and pathology). 1

For sacral lesions specifically:

• Non-contrast MRI accurately depicts the extent of bone destruction, marrow involvement, and any soft tissue extension. 1
• Fluid-sensitive sequences reveal edema patterns that help distinguish between benign processes (like insufficiency fractures) and malignant lesions. 1
• T1-weighted images show the anatomic extent of the lytic lesion and any associated mass. 1

Common Pitfalls to Avoid

Do not order CT as the primary modality for this lesion. While CT without contrast is excellent for cortical bone detail and fracture lines, it is inferior to MRI for characterizing bone marrow pathology and soft tissue involvement in lytic lesions. 1

Avoid ordering "MRI with and without contrast" reflexively. The ACR rates this as "usually not appropriate" (rating 1) for initial evaluation of suspected stress fractures and rates it lower (rating 5-6) for other bone lesions unless there is specific concern for malignancy. 1

Ensure the MRI protocol includes fluid-sensitive sequences (T2 fat-saturated or STIR), not just standard T1 and T2 sequences, as these are critical for detecting marrow edema and inflammatory changes. 1

Differential Diagnosis Considerations

A 1.8cm sacral lytic lesion requires consideration of:

• Metastatic disease (most common cause of lytic bone lesions in adults)
• Multiple myeloma (where MRI depicts bone marrow involvement before lytic destruction occurs) 1, 3
• Primary bone tumors (chordoma is the most common primary sacral malignancy) 4, 5
• Insufficiency fracture (particularly in elderly or osteoporotic patients) 1
• Infection (osteomyelitis or abscess) 2

MRI without contrast effectively distinguishes between these entities in most cases through characteristic signal patterns, enhancement patterns on T2-weighted images, and anatomic distribution. 1

When to Escalate Imaging

If MRI without contrast is non-diagnostic or shows concerning features:

• Consider adding contrast-enhanced sequences to better characterize vascularity and soft tissue involvement. 1
• CT without contrast may be complementary for assessing cortical destruction and planning surgical or interventional approaches. 1
• PET/CT is not routinely indicated for initial characterization but may be useful if metastatic disease or myeloma is confirmed and staging is needed. 1