What are the radiographic findings of tuberculosis of the spine?

Radiographic Findings of Tuberculosis of the Spine

MRI is the gold standard imaging modality for diagnosing spinal tuberculosis, with characteristic findings including destruction of contiguous vertebrae and their endplates, spread along the anterior longitudinal ligament, disc involvement with paraspinal abscess formation, and less commonly, isolated spondylitis without disc involvement. 1

Key Imaging Modalities and Their Findings

MRI Findings

MRI is the most sensitive and specific imaging modality for spinal tuberculosis with a sensitivity of 96% and specificity of 94% 1. Key findings include:

• Vertebral Body Involvement:

  • Destruction of two or more contiguous vertebrae and their opposed endplates
  • Marrow edema appearing as hypointense on T1-weighted images and hyperintense on T2-weighted images
  • T1-weighted sequences are more sensitive than T2-weighted sequences for demonstrating inflammatory processes in tuberculous vertebral bodies 1

• Disc Space Involvement:

  • Disc infection with or without paraspinal mass
  • Disc space narrowing in later stages

• Paraspinal/Epidural Extension:

  • Subligamentous spread along the anterior longitudinal ligament
  • Paraspinal abscess formation ("cold abscess") with peripheral enhancement on contrast-enhanced images
  • Epidural extension causing spinal cord compression
  • Best visualized on gadolinium-enhanced MRI sequences 1

• Patterns of Involvement:

  • Four common patterns: paradiscal (most common), central, anterior subligamentous, and posterior (rare) 2
  • Posterior vertebral arch involvement is uncommon 3

Plain Radiography Findings

Plain radiographs have limited utility in early disease but may show:

• Disc space narrowing
• Vertebral endplate erosion
• Paraspinal soft tissue changes
• Anterior wedging leading to kyphosis and gibbus deformity
• These changes typically lag 3-6 weeks behind clinical symptoms 1

CT Findings

CT provides better bony detail than MRI:

• Bony destruction and fragmentation
• Calcification within abscess
• Vertebral collapse
• Sequestrum formation
• Better visualization of posterior elements when involved 3

Nuclear Medicine Studies

• 3-Phase Bone Scan: Moderate-to-high sensitivity (81.4%) but low specificity (40.7%) 1
• Gallium Scan: Less sensitive (73%) but more specific (61%) than bone scan 1
• FDG-PET/CT: Increased uptake at infection sites with elevated SUV max; useful for monitoring treatment response 2

Distinguishing Features from Other Spinal Infections

Tuberculous spondylitis differs from pyogenic spondylitis by:

1. More extensive bone destruction
2. Relative preservation of disc space until later stages
3. Larger paraspinal abscesses with thin, smooth walls
4. Subligamentous spread across multiple vertebral levels
5. Less prominent reactive sclerosis
6. Calcification within abscess (pathognomonic) 1, 4

Imaging Recommendations for Suspected Spinal TB

1. Initial Imaging:

   • MRI without and with IV contrast of the affected spinal region is the first-line imaging modality 1
   • Plain radiographs may be obtained but have limited sensitivity in early disease 1

2. When MRI is Contraindicated:

   • CT of the spine followed by CT myelography if needed
   • Combined Gallium-67 and Tc-99m-MDP bone scan (sensitivity 73%, specificity 81%) 1

3. For Treatment Monitoring:

   • MRI to assess healing signs: bony ankylosis, resolution of marrow edema, decreased contrast enhancement, and fatty changes within bone marrow 2
   • PET-CT shows promise for response assessment 2

Clinical Correlation with Imaging

Imaging findings should be correlated with:

• Constitutional symptoms (fever, weight loss)
• Back pain and spinal tenderness
• Neurological deficits
• Laboratory markers (elevated ESR, positive interferon-γ release assay)

Important Considerations

• The thoracic spine is most commonly affected, followed by lumbar and cervical regions 5
• Multi-level non-contiguous involvement occurs more frequently than previously recognized 5
• Significant kyphotic deformity can result from anterior column destruction 4, 5
• Image-guided biopsy is recommended for definitive microbiological diagnosis when blood cultures are negative 1

Pitfalls to Avoid

• Relying solely on plain radiographs for early diagnosis
• Failing to image the entire spine when TB is suspected (skip lesions may be present)
• Misinterpreting post-treatment changes as disease progression (structural changes may persist despite clinical improvement)
• Not correlating imaging findings with clinical and laboratory parameters

By understanding these characteristic radiographic findings, clinicians can make an earlier diagnosis of spinal tuberculosis, potentially preventing severe neurological complications and spinal deformities.