Although CT scans are more accessible than MRIs, MRI is more effective in distinguishing between tuberculous and pyogenic spondylitis. Paraspinal abscess formation is observed in both tuberculous and pyogenic spondylitis, but it is more common in tuberculosis (figure 1). MRI with IV contrast is helpful in differentiating the appearance of abscesses. Thick-walled, irregular abscesses are more suggestive of pyogenic spondylitis, whereas tuberculous spondylitis typically causes a thin-walled paraspinal abscess (figure 2).

The abscess border also provides clues: ill-defined borders are seen in pyogenic abscesses, while well-defined borders are indicative of tuberculous abscesses (figure 3). Pyogenic abscesses typically involve the entire vertebral spine, whereas tuberculosis more commonly affects the thoracic spine. Multilevel vertebral involvement and subligamentous spread extending more than three levels are indicators of tuberculous spondylitis.

Epidural abscesses can be seen in both tuberculous and pyogenic spondylitis (figure 4), but recent observations indicate that the anterior meningovertebral ligament tends to remain intact in tuberculosis epidural abscesses (figure 5). This could serve as an additional clue to help differentiate between the pyogenic and tuberculous causes of spondylitis.

Severe destruction and gibbus deformity, as a focal kyphosis, are more suggestive of tuberculous spondylitis, but they are not characteristic, as other pathogens can also cause vertebral deformities.

Involvement of other organs in tuberculous spondylitis is also a useful diagnostic clue (figure 6).

Key MRI features include:

• Well-defined paraspinal abnormal signal in TB versus ill-defined abnormal signal in pyogenic spondylitis (Figure 7).
• Thin, smooth abscess wall in TB versus thick, irregular abscess wall in pyogenic spondylitis.
• Paraspinal or intraosseous abscess is more common in TB.
• Spread to >3 vertebral levels in TB versus spread to <3 vertebral levels or no spread in pyogenic spondylitis.
• Involvement of multiple vertebral bodies in TB.
• Thoracic spine involvement is more frequent in TB.
• Intact anterior meningovertebral ligament is more common in TB.