What is the sensitivity of a Skeletal Magnetic Resonance Imaging (MRI) for detecting lytic lesions?

Sensitivity of Skeletal MRI for Lytic Lesions

MRI has lower sensitivity than CT for detecting lytic bone lesions, but excels at identifying bone marrow infiltration before cortical bone destruction occurs. 1

Direct Comparison of Sensitivity

MRI vs. CT for Lytic Lesions

• CT is superior to MRI for detecting actual lytic bone destruction, as MRI primarily depicts bone marrow involvement rather than cortical bone loss 1
• MRI detects bone marrow infiltration (focal lesions representing plasma cell infiltration) while CT reveals the actual lytic lesions (bone destruction) 2
• In a study of 28 newly diagnosed multiple myeloma patients, PET/CT and MRI had equivalent sensitivity (50% concordance) for detecting lesions in the spine and pelvis, but PET/CT detected 25% more lytic bone lesions located outside the MRI field of view 3

Why MRI Misses Lytic Lesions

• Lytic lesions only become visible on conventional imaging after more than 30-50% of trabecular bone has been lost 2, 4
• MRI can show focal bone marrow lesions without corresponding bone destruction visible on CT—in one study, only 59.3% of focal lesions seen on MRI had corresponding osteolytic areas on CT 5
• Neither morphological characteristics (size, location) nor texture features of MRI focal lesions could predict whether corresponding bone destruction would be present on CT 5

Clinical Context: When MRI is Superior

Early Disease Detection

• MRI detects bone marrow involvement before lytic destruction occurs, making it essential for risk-stratifying smoldering myeloma patients 1
• In asymptomatic patients without radiologic evidence of lytic lesions, MRI can identify initial bone marrow infiltration that conventional imaging misses 6
• The presence of ≥2 focal lesions measuring ≥5 mm on MRI is a myeloma-defining event, even without visible lytic bone destruction 1

Specific Anatomic Advantages

• MRI is the gold standard for detecting spinal cord compression 1
• MRI is superior to PET/CT in diagnosing infiltrative patterns in the spine (25% of cases show infiltration on MRI that is negative on PET/CT) 3

Guideline-Based Imaging Algorithm

Initial Diagnostic Workup

• Whole-body low-dose CT (WBLD-CT) is the standard procedure for diagnosing lytic disease (Grade 1A recommendation) 1
• WBLD-CT detects up to 60% more relevant findings than conventional radiography and identifies small (<5 mm) lytic lesions 1, 2
• FDG-PET/CT is an acceptable alternative if the CT component has imaging quality equivalent to WBLD-CT 1

When to Add MRI

• In asymptomatic patients with no lytic disease on WBLD-CT, whole-body MRI (or spine and pelvic MRI) must be performed 1
• MRI is first-line for suspected solitary plasmacytoma of bone 1
• MRI is mandatory when spinal cord compression is suspected 1

Critical Pitfalls to Avoid

Don't Rely on MRI Alone for Lytic Lesions

• MRI depicts bone marrow involvement, not actual bone destruction—you need CT to assess lytic lesions, fracture risk, and cortical integrity 1, 2
• A patient can have myelomatous bone marrow involvement on MRI without lytic bone destruction on CT 2

Don't Skip CT When MRI Shows Focal Lesions

• 40.7% of focal lesions visible on MRI in the axial skeleton have no corresponding osteolytic destruction on CT 5
• CT is essential for surgical planning, radiation therapy planning, and assessing areas at risk of pathologic fracture 1

Field of View Limitations

• Standard spine and pelvis MRI misses 25% of lytic bone lesions located in the skull, ribs, and appendicular skeleton that are visible on whole-body imaging 3
• Skull and rib lesions are not well detected by MRI compared to CT or skeletal surveys 1

Quantitative Sensitivity Data

• Plain radiographs require 30-50% trabecular bone loss before lytic lesions become visible 1, 2, 4
• WBLD-CT detects lesions with <5% trabecular bone destruction 7
• MRI sensitivity for lytic lesions is lower than CT, but MRI detects bone marrow infiltration before any cortical destruction occurs 1
• In comparative studies, MRI and PET/CT had equivalent sensitivity for spine/pelvis lesions, but both missed lesions outside their respective fields of view 3