Percival Pott was the first person to present the classic description of spinal tuberculosis in 1779; hence, spinal TB was called 'Pott's Disease [1]. Predisposing factors for tuberculosis include poverty, overcrowding, illiteracy, malnutrition, alcoholism, drug abuse, diabetes mellitus, immunosuppressive treatment and HIV infection. These are predisposing factors for spinal tuberculosis as well [2].

Spinal involvement is usually the result of hemato-genous spread of M. tuberculosis into the dense vasculature of cancellous bone of the vertebral bodies. The primary infection site is either a pulmonary lesion or an infection of the genitourinary system [3-4]. Spread occurs either via the arterial or the venous route.

This vascular plexus facilitates hematogenous spread of the infection in the paradiscal regions. Batson's paravertebral venous plexus in the vertebra is a valve-less system that allows free flow of blood in both directions depending upon the pressure generated by the intra-abdominal and intrathoracic cavities following strenuous activities like coughing. In patients with noncontiguous vertebral tuberculosis, again it is the vertebral venous system that spreads the infection to multiple vertebrae [5].

Spinal tuberculosis is initially apparent in the anterior inferior portion of the vertebral body. Later on it spreads into the central part of the body or disk. Paradiskal, anterior and central lesions are the common types of vertebral involvement. A lack of proteolytic enzymes in mycobacterial infections (in comparison with pyogenic infections) has been suggested as the cause of the of the subligamentous spread of infection [2, 6].

In spinal tuberculosis, characteristically, there is destruction of the intervertebral disk space and the adjacent vertebral bodies, collapse of the spinal elements and anterior wedging leading to the characteristic angulation and gibbus (palpable deformity because of involvement of multiple vertebrae) formation.

The upper lumbar and lower thoracic spine are most frequently involved sites. More than one vertebra is typically affected, and the vertebral body is more frequently affected than the posterior arch [7]. Distortion of spinal column leads to spinal deformities [5]. Paraplegia is the most devastating complication of spinal tuberculosis.

• Patients with pacemaker/cochlear implant in-situ.
• Patients with claustrophobia/ any other psychiatric abnormality.

Technique: Plain radiograph of spine of involved area was first done in all cases followed by evaluation on SIEMENS 1.5 TESLA MRI superconducting magnet.

Initially non contrast T1 weighted (T1W), T2 weighted (T2W) and short tau inversion recovery (STIR) sequences in axial, sagittal and coronal planes of the involved spine were taken. Then post-contrast T1 sequence was obtained by using intravenous administration of gadodiamide (GdDTPA-BMA) of 0.1 mmol/kg doses, in axial, coronal and sagittal planes. The characteristic radiological features on plain radiograph and MRI along with response to treatment was considered diagnostic of Pott’s spine; however wherever possible cytopathological or histopathological findings (specimen of decompression surgery or percutaneous aspiration/biopsy) were considered diagnostic of the condition.

In our study age distribution ranged from 06- 70 years. Maximum patients belonged to the age group 31- 40 years (35%) followed by 41-50 years (17.5 %) then by 51-60 years (12.5%). The number of patients in other age groups was significantly less. The mean age of our study was 40.

Level of lesion on MRI: In our study, lower thoracic (32.50%) and lumbar (40%) spine were most common sites of involvement accounting for 72.5% patients followed by upper thoracic spine (25%). Cervical and sacral spine involvement was seen in only 15% patients.

Table-1: Level of lesion on MRI

T1WI and T2WI/STIR sequence signal intensities on MRI: In our study, most of the lesions were hypointense on T1 (87.5%) and all of these lesions were hyperintense on T2/STIR (100%). These results were statistically highly significant.

The X-ray when compared to MRI was found to have a sensitivity of 28.57% and a specificity of 92.31%in detection of paravertebral widening/psoas abscess.

Figure -1: Plain x- ray film –AP and Lateral view dorsal and lumbar spine –adjacent end plate irregularity at L1 and D12 vertebrae and reduced height of L1 vertebra seen. Disc space narrowing between L1 and D12 vertebra is seen.

Figure-2: T1W SAG- Compression collapse of L1vertebra is seen with End plate irregularity and destruction of intervening disc between D11, D12,

Figure-4: T2W axial- pre/paravertebral mass and epidural soft tissue component are seen. (same patient as in Figure 3).

Figure-5: Plain x ray- AP and Lateral view-no disc space narrowing and end plate irregularity seen.

Figure-6: T1 SAG- D5 vertebra is hypointense in signal intensity. A large posterior epidural mass (yellow arrow), isointense in signal intensity is seen from D1 toD8 vertebral level causing anterior displacement and compression of spinal cord. (same patient as in Figure 5).

A total of 40 patients with strong suspicion of spine tuberculosis were evaluated using MR imaging and x-ray. In our study age distribution ranged from 06-70 years. Maximum patients belonged to the age group 31- 40 years (35%) followed by 41-50 years (17.5%) then by 51-60 years (12.5%). The number of patients in other age groups was significantly less.

The mean age of our study was 40. Similar observation was made by Lifeso et al [11] where the mean age was 41.8 years.

Comparison on X-RAY and MRI: In our study, the comparison of X-ray and MRI for evaluating spinal TB on the basis of end plate irregularity, thecal sac compression, cord compression and cord changes was statistically highly significant.

It was statistically significant on the basis of Disk Space Narrowing/Disk Involvement, paravertebral Widening/ Psoas abscess and Posterior Element Involvement. However, the comparison on the basis of vertebral height and kyphotic deformity was statistically not significant.

Hence it was concluded that overall the comparison of X-ray and MRI for evaluating spinal TB was highly significant. Similar result was seen in study conducted by Kukreja et al [23] that imaging evaluation of patients with spinal TB showed that disk involvement, abscess and end plate irregularity were statistically better visualized on MRI as compared to X-ray.

Spinal canal narrowing, cord compression and compressive myelopathy could only be commented upon on MRI. Thecal sac indentation, spinal cord compromise/ canal stenosis and cord edema which are important findings for deciding patient management and future prognosis were picked up only on MRI. In the study conducted by Yasaratne et al [22] that the earliest feature of tubercular spondylitis was end plate involvement and oedema, which was detected on MRI whereas plain x-ray images were helpful in identifying fusiform paraspinal soft tissue swelling and vertebral collapse in advanced cases.

In the study conducted by Ansari et al [8] (2013) it was concluded that MRI was better than X-Rays to visualize intervertebral disk involvement.

Limitation: There was no information about the HIV status of the patients.

Both Plain X-Rays and MRI are important imaging modalities for diagnosis of spinal tuberculosis and are also useful to monitor the response of the patients to the treatment. Plain X-ray remains the primary and the first imaging modality to evaluate the disease. Plain radiography has few shortcomings in that radiographs generally remain normal in the early stages of the disease, hence by the time the disease is evident on plain X-Ray, the patient has already reached an advanced stage.