Should a bone scan be ordered in a patient with a suspected underlying malignancy and conflicting imaging results, where a computed tomography (CT) scan suggests possible bone metastasis but a follow-up magnetic resonance imaging (MRI) scan shows no suspicious osseous lesions?

No, a bone scan should not be ordered in this scenario

When a follow-up MRI shows no suspicious osseous lesions after a CT suggested possible bone metastasis, a bone scan is not indicated and would provide no additional clinical benefit. MRI is superior to bone scintigraphy for detecting bone metastases, and the negative MRI effectively resolves the equivocal CT finding 1.

Why MRI Supersedes the Need for Bone Scan

MRI's Superior Diagnostic Performance

• MRI is more sensitive than bone scintigraphy for detecting skeletal metastases, particularly in the spine and bone marrow 1, 2
• In a study of 106 cancer patients, MRI detected focal bone abnormalities in 28% of cases that were completely missed by bone scintigraphy, while bone scan only detected one lesion that MRI missed 2
• MRI directly visualizes bone marrow components and can distinguish between benign and malignant processes, whereas bone scintigraphy only shows indirect metabolic activity 3

The Limited Role of Bone Scan

• According to ACR Appropriateness Criteria, bone scan plays only a limited role when evaluating bone lesions already assessed by MRI and CT 1
• Bone scintigraphy has low specificity (81%) and requires confirmation with other imaging modalities like MRI or CT when findings are equivocal 1, 4
• The guideline explicitly states that radiographic evaluation (not bone scan) is the recommended next step for bone lesions found on MRI and CT 1

The Appropriate Next Steps

If Clinical Suspicion Remains High

• Consider PET/CT if there is persistent clinical concern despite negative MRI, as it has superior sensitivity (90%) and specificity (97%) compared to bone scan 4
• PET/CT is now recommended as the single most comprehensive test for detecting bone metastases, effectively replacing the combination of bone scan plus CT 5, 4

If the MRI Was Limited in Scope

• Ensure the MRI adequately covered the region of concern identified on CT 1
• If the CT finding was in an area not fully evaluated by MRI, targeted MRI of that specific region would be more appropriate than bone scan 1

Clinical Correlation is Essential

• Review the specific CT finding that raised concern - was it truly suspicious for metastasis or merely an incidental finding? 1
• Assess for symptoms: localized bone pain, elevated bone-specific alkaline phosphatase (B-ALP), or neurologic symptoms would warrant additional evaluation 5, 4, 6
• Consider the primary malignancy type and stage - certain histologies like myxoid liposarcoma have higher rates of bone metastases 1

Common Pitfalls to Avoid

• Do not reflexively order bone scan when cross-sectional imaging is negative - this represents outdated practice patterns 1
• Avoid the false reassurance of a negative bone scan - it is less sensitive than MRI and could miss early marrow-based metastases that MRI would detect 2, 3
• Do not order multiple overlapping imaging studies without clear indication - this increases cost, radiation exposure, and potential for false-positive findings requiring further workup 1

The negative MRI effectively rules out the CT concern for bone metastasis in this scenario, and adding a bone scan would be redundant and potentially misleading 1, 2.