What are the characteristic MRI findings of vertebral osteomyelitis?

MRI Findings of Vertebral Osteomyelitis

The hallmark MRI finding of vertebral osteomyelitis is the inability to distinguish margins between the disc space and adjacent vertebral marrow on T1-weighted images, associated with increased signal intensity from the disc and adjacent involved marrow on T2-weighted images. 1

Key MRI Features of Vertebral Osteomyelitis

T1-Weighted Imaging Findings

• Decreased signal intensity in vertebral body marrow (95% of cases) 2
• Loss of endplate definition (95% of cases) 2
• Inability to distinguish margins between disc space and adjacent vertebral marrow 1

T2-Weighted/Fluid-Sensitive Imaging Findings

• Increased signal intensity in the disc (95% of cases) 2
• Increased signal intensity in adjacent involved marrow (56% of cases) 2
• Subperiosteal fluid collection may be present 1

Contrast Enhancement Patterns

• Enhancement of the disc and vertebral body (94% of cases with contrast) 2
• Ring enhancement of paraspinal/epidural processes correlates with abscess 2
• Homogeneous enhancement correlates with phlegmon 2
• Gadolinium enhancement may be the first sign of acute inflammatory process 1

Extension of Infection

• Extension to paravertebral space causing epidural or paravertebral abscess is best visualized on gadolinium-enhanced MRI 1
• MRI can detect extension of infection to soft tissues, spinal canal, and neural structures 1, 3

Diagnostic Accuracy

• MRI has a sensitivity of 97%, specificity of 93%, and accuracy of 94% in diagnosing vertebral osteomyelitis 1
• MRI has a 100% negative predictive value for excluding osteomyelitis; normal marrow signal reliably excludes infection 1

Special Considerations

Timing of MRI

• Initial MRI may be negative if performed too early (within 2 weeks of symptom onset) 4
• Consider repeat MRI 2-4 weeks after symptom onset if clinical suspicion remains high 4

Differential Diagnosis

• MRI can differentiate vertebral osteomyelitis from degenerative, traumatic, or neoplastic diseases 1
• Unusual patterns may mimic metastases, with the "rim sign" (peripheral low signal intensity) and "halo sign" (peripheral high T2 signal) being helpful distinguishing features 5

Specific Pathogen Considerations

• In tuberculous or brucellar vertebral osteomyelitis, T1-weighted sequences appear more sensitive than T2-weighted sequences 1
• Radiographic findings suggestive of tuberculosis include:
  • Destruction of 2+ contiguous vertebrae and their endplates
  • Spread along anterior longitudinal ligament
  • Disc infection with/without paraspinal mass 1

Alternative Imaging When MRI is Contraindicated

• Combination spine gallium/Tc99 bone scan
• CT scan
• Positron emission tomography (PET) scan 1

Clinical Correlation

• MRI findings should be interpreted in conjunction with clinical presentation, laboratory markers (ESR, CRP), and blood cultures 3
• Image-guided aspiration biopsy is recommended in patients with suspected vertebral osteomyelitis when a microbiologic diagnosis has not been established by blood cultures 1

Pitfalls and Caveats

• Early vertebral osteomyelitis may not show characteristic MRI findings
• Prior antibiotic treatment may alter imaging appearance
• Patients with implantable devices cannot undergo MRI
• Distinguishing between infection and reactive inflammation can be challenging
• Vertebral osteomyelitis can have MRI patterns mimicking osseous metastases 5

MRI remains the gold standard imaging modality for diagnosing vertebral osteomyelitis, with its excellent soft tissue contrast and ability to detect early marrow changes before they become apparent on other imaging modalities.