What are the classic radiological features of spinal tuberculosis (Pott disease)?

Classic Radiological Features of Spinal Tuberculosis (Pott Disease)

The hallmark radiological signs of spinal tuberculosis include destruction of two or more contiguous vertebrae with their opposed endplates, spread along the anterior longitudinal ligament, disc involvement with or without paraspinal abscess formation, and less commonly, spondylitis without disc involvement. 1

Key Diagnostic Imaging Features

Primary MRI Findings

MRI without and with IV contrast is the imaging modality of choice for diagnosing spinal tuberculosis, demonstrating 96% sensitivity, 94% specificity, and 92% accuracy. 2, 1 The critical diagnostic features include:

• Vertebral body destruction: Two or more contiguous vertebrae show destruction of their opposed endplates, which is the classic pattern distinguishing TB from typical bacterial infections 1, 2

• Anterior longitudinal ligament spread: The infection characteristically spreads along the anterior longitudinal ligament, creating subligamentous extension 1, 2

• Disc involvement: Intervertebral disc infection occurs in approximately 95% of cases, often with preservation of disc height initially (unlike pyogenic infections) 3

• Paraspinal abscess formation: Mixed soft tissue fluid collections or "cold abscesses" are hallmark features, seen in 96.25% of cases 3, 4

Important Technical Considerations

• T1-weighted sequences are more sensitive than T2-weighted sequences in demonstrating inflammatory processes in vertebral bodies specifically for tuberculous spondylitis 1, 2

• Gadolinium contrast enhancement is essential for delineating epidural abscesses, paravertebral collections, and assessing the full extent of disease 2, 5

• Epidural enhancement combined with abnormal laboratory values is highly predictive of positive biopsy results for tuberculous spondylodiscitis 2

Anatomical Distribution Patterns

• Thoracic spine involvement is most common (48.5% of cases), followed by lumbar (39.4%) and cervical spine (12.1%) 3, 6

• Contiguous two-vertebral involvement represents the most frequent pattern 3

• Skip lesions (non-contiguous multilevel disease) occur in approximately 5% of cases and are more common than previously recognized 3, 4

Atypical Presentations to Recognize

Posterior Element Involvement

• Isolated posterior element tuberculosis can occur without anterior column involvement, affecting laminae (72.7%), pedicles (60.6%), articular processes (57.5%), and spinous processes (57.5%) 6

• This atypical pattern is frequently misdiagnosed as neoplasm on non-contrast imaging 5, 6

Spondylitis Without Disc Involvement

• Less commonly (approximately 5% of cases), tuberculous spondylitis presents without disc space involvement, mimicking neoplastic disease 1

• This pattern requires high clinical suspicion and often necessitates biopsy for definitive diagnosis 5

Complications Visible on Imaging

• Epidural abscess formation occurs in 62.5% of cases and is best visualized on gadolinium-enhanced MRI 3

• Spinal cord compression or displacement is seen in significant proportions of patients, with cord edema present in 15% of cases 3

• Gibbus deformity (anterior wedging and kyphosis) results from vertebral collapse and is characteristic of advanced disease 4, 7

Critical Diagnostic Pitfalls to Avoid

• Never rely on non-contrast MRI alone when tuberculosis is suspected—contrast enhancement patterns are essential for distinguishing TB from neoplasm and assessing abscess formation 2, 5

• Plain radiographs lag 3-6 weeks behind clinical symptoms and show bone destruction only in advanced disease, making them inadequate for early diagnosis 1

• CT without contrast provides excellent osseous detail but misses critical marrow pathology and soft tissue involvement; it should complement, not replace, MRI 1

Diagnostic Algorithm for Suspected Spinal TB

• Step 1: Order MRI of the spine without and with IV contrast as the first-line imaging study in any patient with subacute back pain from endemic regions or with risk factors 2, 1

• Step 2: Perform PPD test or interferon-γ release assay (which has higher sensitivity, especially in immunocompromised patients) in patients with characteristic radiologic findings 1

• Step 3: If MRI cannot be performed due to contraindications, obtain combined gallium-67/Tc-99m bone scan (sensitivity 78%, specificity 81%) 1

• Step 4: When imaging is equivocal or atypical patterns are present, proceed with CT-guided biopsy for histopathological confirmation—this is the gold standard for definitive diagnosis 4, 5

Distinguishing TB from Pyogenic Infection

• Tuberculous spondylitis typically shows relative disc preservation early, subligamentous spread, larger paraspinal abscesses, and multilevel involvement more frequently than pyogenic infections 1, 7

• Pyogenic spondylitis demonstrates rapid disc destruction, smaller abscesses, and single-level involvement more commonly 7

• When differentiation is uncertain, obtain tissue diagnosis through image-guided or surgical biopsy, as clinical and imaging findings alone may be unreliable 5