Thin Black Line Through Soft Tissue and Bone on Elbow MRI
A thin black line traversing both soft tissue and bone on an elbow MRI most likely represents an imaging artifact, specifically a susceptibility artifact from metallic foreign body, motion artifact, or chemical shift artifact—rather than true pathology—since genuine fracture lines do not extend continuously through both soft tissue and bone with uniform signal characteristics.
Understanding the Finding
The key to interpreting this finding lies in recognizing that true pathologic processes respect tissue boundaries and have characteristic signal patterns on MRI 1, 2:
- Fracture lines appear as dark (hypointense) lines on all sequences but are confined to bone, with associated bone marrow edema appearing as high signal on T2-weighted images 3
- Soft tissue tears (ligaments, tendons) show disruption of normal architecture with fluid signal intensity, not uniform black lines 4, 5
- A continuous black line through disparate tissue types suggests artifact rather than pathology 2
Differential Considerations
Most Likely: Imaging Artifact
Susceptibility artifacts from metallic objects create signal voids (black lines) that can extend across multiple tissue planes without respecting anatomic boundaries 1, 2:
- Previous surgical hardware, metallic foreign bodies, or even clothing fasteners can cause this appearance
- These artifacts characteristically appear as uniform signal voids on all sequences
- They may create geometric distortion patterns
Motion artifact can create linear signal voids if the patient moved during image acquisition 2
Less Likely but Consider: True Pathology
If this represents actual pathology, the differential narrows significantly 3:
- Stress fracture with periosteal reaction: MRI findings include bone marrow edema and/or periosteal fluid, but the fracture line itself remains confined to bone 3
- Loose body: May appear as low signal on all sequences, but would be discrete and intra-articular, not a continuous line 3
- Heterotopic ossification: MRI is less sensitive than radiographs for this finding, and it would not create a linear pattern through soft tissue 3
Recommended Approach
- Review the technical quality of the MRI study—check for patient motion, metallic artifacts, or field inhomogeneity
- Correlate with radiographs: Plain films remain the first-line imaging for elbow pathology and are superior for detecting fractures, loose bodies, and heterotopic ossification 3, 6
- Examine adjacent sequences: True pathology will have consistent findings across multiple pulse sequences with characteristic signal patterns 1, 5
If radiographs are normal and clinical suspicion remains high 3:
- For suspected occult fracture: MRI is as sensitive as 3-phase bone scan, with findings of bone marrow edema and/or periosteal fluid at the abnormality site 3
- For suspected ligament or tendon injury: MRI has high sensitivity (90-100%) for detecting UCL injuries and epicondylalgia 6, 4
- Consider repeat imaging with different parameters or at a different facility if artifact is suspected
Critical Pitfalls to Avoid
Do not assume a linear black signal represents pathology without 1, 2, 5:
- Confirming the finding on multiple sequences and planes
- Correlating with plain radiographs
- Assessing for associated findings (edema, effusion, soft tissue changes)
- Reviewing patient history for prior surgery or metallic exposure
Remember that MRI has specific limitations 3:
- MRI is less sensitive than radiographs for heterotopic ossification and calcification 3
- MRI has limited accuracy for cartilage defects (18-64% depending on location) 3
- Small intra-articular bodies may be better visualized on CT arthrography 3
When to Pursue Additional Imaging
Consider CT if 3:
- Detailed bony anatomy assessment is needed
- Heterotopic ossification or loose bodies are suspected
- MRI findings remain equivocal and clinical symptoms suggest bony pathology