Spine is the most common site of skeletal metastases, with thoracic spine > lumbar > cervical involvement. Early detection is crucial to prevent neurological compromise and guide oncologic management. MRI is the gold standard for evaluating spinal metastases due to its high sensitivity for bone marrow, soft tissue, and spinal cord involvement.
📌 Why MRI?
- Detects early marrow infiltration before cortical bone destruction.
- Superior to CT/X-ray for cord compression, epidural disease, and paraspinal extension.
- Multiplanar imaging + contrast helps in surgical and radiation planning.
🔍 MRI Sequences for Spine Metastases
- T1-weighted (T1W):
- Normal marrow is hyperintense due to fat.
- Metastases = hypointense, focal or diffuse.
- T2-weighted (T2W):
- Variable signal (often hyperintense).
- Surrounding soft tissue edema visible.
- STIR / Fat-Suppressed T2:
- Highly sensitive for marrow infiltration (hyperintense lesions).
- Post-contrast T1 + FS:
- Enhancing lesions, epidural/paraspinal extension.
- Diffusion-weighted imaging (DWI):
- Hyperintense metastatic foci, restricted diffusion.
📍 MRI Findings in Spine Metastases
- Bone Marrow Changes
- Focal or diffuse hypointense lesion on T1.
- Hyperintense on STIR/T2.
- Replacement of normal marrow fat.
- Vertebral Collapse
- Metastatic collapse:
- Convex posterior border of vertebral body.
- Involvement of posterior elements.
- Paraspinal/epidural soft tissue mass.
- Osteoporotic collapse (differential):
- Preserved posterior wall.
- No soft tissue mass.
- Metastatic collapse:
- Soft Tissue Involvement
- Epidural mass compressing spinal cord.
- Paravertebral soft tissue component.
- Cord and Nerve Root Involvement
- Direct cord compression → T2 hyperintensity, cord edema, myelopathy.
- Nerve root encasement.
⚡ Differentials to Consider
- Osteoporotic fracture.
- Infective spondylitis (TB, pyogenic).
- Primary bone tumors.
📌 Teaching Pearls
- T1 hypointensity + STIR hyperintensity = classic for metastasis.
- Always assess three compartments: vertebral body, epidural space, paraspinal tissues.
- MRI is first-line in suspected cord compression.
- Differentiate metastatic vs benign compression fractures carefully.
Osteoporotic vs Metastatic Vertebral Collapse on MRI
| Feature | Osteoporotic (Benign) Collapse | Metastatic (Malignant) Collapse |
|---|---|---|
| Posterior vertebral wall | Maintained / concave | Convex bulge into canal |
| Signal on T1 | Preserved marrow fat (normal hyperintensity or only mild edema) | Diffuse or focal hypointensity due to marrow replacement |
| Signal on STIR/T2 | Mild hyperintensity (edema), no mass | Intense hyperintensity, often with paraspinal/epidural mass |
| Enhancement | Minimal or patchy | Strong, heterogeneous enhancement |
| Involvement of posterior elements | Rare | Common |
| Paraspinal/epidural soft tissue mass | Absent | Present |
| Multiple vertebral levels | Usually single | May be multiple contiguous/noncontiguous lesions |
| Line of fracture | Band-like low signal fracture line, no marrow replacement | Marrow infiltration without clear fracture line |
| Diffusion (DWI) | No restricted diffusion | Restricted diffusion (hyperintense on DWI) |
✅ Key takeaway:
- Osteoporotic collapse = fracture line + preserved marrow fat + no mass.
- Metastatic collapse = marrow replacement + convex posterior wall + soft tissue mass.
