Revisiting imaging features of spinal tuberculosis

INTRODUCTION Tuberculosis remains one of the top ten causes of death worldwide, with the largest number of cases occurring in Southeast Asia.[1] This is driven by continued community transmission, ageing populations, increased population mobility, and the rising threat of multidrug-resistant tuberculosis.[2] Even though tuberculosis most commonly affects the lungs, it can also manifest as extrapulmonary disease, often involving the spine,[3] which may result in significant morbidity, such as spinal deformities and irreversible neurological sequelae, if left untreated. The Mycobacterium tuberculosis complex comprises a group of organisms that cause tuberculosis, such as M. tuberculosis, M. bovis and M. africanum. Although these species show phenotypic differences, they are genetically very similar. Other pathogenic mycobacteria include the M. avium complex and non-tuberculous mycobacteria, which are common opportunistic pathogens. These organisms appear as gram-positive, non-spore-forming, non-motile, rod-shaped bacteria.[4] Most patients with tuberculosis acquire the infection through the inhalation of airborne droplet nuclei containing the M. tuberculosis complex. Spinal tuberculosis is thought to arise from the haematogenous spread of organisms into cancellous bone of the vertebral bodies from the lungs or genitourinary system.[5] This can occur via the arterial or the venous system. Spinal tuberculosis predominantly affects the thoracic and lumbar spine, and less commonly involves the cervical spine and sacrum.[6,7] It is frequently characterised by paradiscal vertebral body destruction with resultant kyphosis. Intervertebral discs are usually affected only in late stages of the disease. This differs from pyogenic spondylodiscitis, where there is early involvement of the intervertebral discs. The relative preservation of intervertebral discs in spinal tuberculosis has been attributed to the lack of proteolytic enzymes in mycobacteria compared to organisms causing pyogenic infections.[8] Spinal tuberculosis can also result in pathological fracture with kyphosis and epidural abscess formation, potentially leading to spinal cord compression and neurological sequelae.[9] The onset of spinal tuberculosis tends to be slow and insidious, with disease progression ranging from a few months to several years. Some patients may develop constitutional symptoms, such as fever, night sweats, weight loss, malaise and generalised body aches. However, most patients usually seek medical attention only when the disease has progressed, causing back pain, spinal deformity or neurological symptoms.[5] The importance of imaging in the diagnosis and management of spinal tuberculosis has increased over the years. Imaging is a valuable diagnostic tool for early detection of infection and for differentiating bacterial from tuberculous infection, which can be subsequently confirmed by histopathology. Early recognition allows prompt initiation of treatment to minimise the extent of spinal involvement and prevent the development of serious neurological injury. Imaging can also assess the extent of disease, identify complications, guide patient management, and enable follow-up of disease progression or resolution after treatment. Knowledge of the range of spinal tuberculosis imaging morphology across modalities is useful for early detection of the disease. This article reviews the broad spectrum of imaging findings on radiography, computed tomography (CT) and magnetic resonance imaging (MRI), and outlines the specific patterns of disease manifestation in spinal tuberculosis. FINDINGS ACROSS IMAGING MODALITIES Radiography Radiography remains the cornerstone of initial spinal imaging, serving as a quick screening tool for general or vague back symptoms. The radiological features of advanced spinal tuberculosis have been shown to be consistent in more than 90% of cases.[10] Classic findings include disc space narrowing and osseous destruction [Figures 1a & 2a]. Multiple vertebrae may be involved with collapse or fusion of the vertebrae.[5] Scalloping of the anterior vertebral body may be detected due to spread beneath the anterior longitudinal ligament. Tuberculosis abscesses can present as widening of the prevertebral soft tissue in the cervical spine. In the thoracic and lumbar spine, widening of the thoracic paravertebral stripe and outward asymmetrical bulge of the psoas muscle may be observed, respectively [Figures 1a & 2a].Figure 1: A 38-year-old man with COVID-19 infection and upper back pain. (a) Chest radiograph shows subtle T8 vertebral height loss with narrowing of T8–T9 disc space (arrowhead) and widening of the paravertebral stripes (arrows). (b) Sagittal CT image of thoracic spine shows paradiscal bone destruction of the inferior T8 and superior T9 vertebral endplates and sclerosis in the vertebral bodies (arrow). (c) Contrast-enhanced axial CT image of the chest shows a thin, rim-enhancing collection in the right T8 prevertebral region (arrowhead) with slight extension into the epidural space (arrow).Figure 2: A 36-year-old woman with a 3-month history of worsening back pain, weight loss and persistent fever. (a) Radiograph of the thoracic spine shows a T9 vertebral body fracture (arrowhead) and widening of the paravertebral stripe extending from T8 to T12 (arrows). (b) Post-contrast sagittal T1-W fat-saturated MR image of the thoracic spine shows a pathological T9 fracture with near-complete collapse (arrow). A prevertebral abscess with subligamentous spread from T8 to T10 and anterior scalloping of the vetebral bodies (arrowhead) are also seen.As radiographs often appear normal in the early stages of the disease, it is estimated that at least one-third of calcium must be lost in an area for osteolysis to be detected radiographically.[5] There is also difficulty in assessing the extent of disease, as the number of vertebral bodies involved may be underestimated. Assessment of disease complications, such as soft tissue involvement and spinal cord compression, is also limited on plain radiographs. Computed tomography Computed tomography complement radiographs in further investigation of suspected spinal tuberculosis. Owing to its multiplanar capabilities and high resolution, CT allows earlier detection of vertebral involvement and better visualisation and localisation of bony destruction. Bone destruction may present as a localised lytic or sclerotic pattern and can be subperiosteal [Figures 1b & 3a]. Paraspinal abscesses and soft tissue involvement are also better appreciated on CT with contrast administration [Figures 1c & 4]. The presence of calcification within the abscess is diagnostic of spinal tuberculosis.[5] It is also useful in delineating the extent of inflammatory tissue, collection, disc or bone involvement [Figure 5a & b].[7] In addition, CT is now widely used to guide biopsy of spinal lesions because of its high accuracy and low risk of complications [Figure 6b].Figure 3: A 29-year-old woman with bilateral lower limb numbness and weakness. (a) Sagittal CT image of the thoracic spine shows bony destruction of T9 and T10 vertebral bodies, resulting in kyphosis and gibbus deformity (arrow), along with bony destruction of T5, T6 and T11 vertebrae (arrowheads). (b) Sagittal TIRM sequence MR image of the thoracic spine shows skipped lesions with bone marrow oedema and bone destruction involving T5, T6 and T9 to T11 vertebral bodies (arrowheads). Retropulsion of a T10 pathological fracture results in thoracic cord compression and cord oedema (arrow). (c) Postcontrast sagittal T1-W fat-saturated MR image shows intraosseous abscesses in T5, T6, T9 and T10 vertebral bodies (arrowheads) and rim-enhancing prevertebral and epidural collections from T9 to T11 (arrow).Figure 4: A 35-year-old man with sacral pain, fever and weight loss. Contrast-enhanced axial CT image of lumbar spine shows a multilobulated rim-enhancing collection in the sacral region invaginating the sacral foramina (arrow) with bone erosion (arrowhead).Figure 5: A 48-year-old woman with right gluteal and left flank masses. (a) Contrast-enhanced axial CT image of the lumbar spine shows bilateral psoas muscle rim-enhancing collections (arrows), left posterior lumbar rim-enhancing subcutaneous collection (black arrowhead) and bony destruction of the L3 vertebral body (white arrowhead). (b) Sagittal CT image of the lumbar spine shows a sclerotic lesion in the L3 vertebral body with bone erosion (arrow). Gross destruction and pathological fractures of S2 and S3 vertebrae (arrowhead) are also seen. (c) Sagittal T2-W MR image of the thoracolumbar spine shows a pathological fracture of the L3 vertebral body with subligamentous spread of the prevertebral abscess to adjacent lumbar vertebrae and the sacrum (arrowheads). Bone destruction of the sacrum is also seen (arrow). (d) Postcontrast sagittal T1-W fat-saturated MR image shows a large rim-enhancing subcutaneous collection in the posterior lumbar spine extending to the lower thoracic region (arrow). Presacral rim-enhancing collection (arrowhead) is seen. (e) Coronal T2-W fat-saturated MR image shows collections in bilateral psoas muscles (arrows). (f) Postcontrast axial T1-W MR image of the pelvis shows rim-enhancing prevertebral collections in bilateral psoas muscles (arrows) and bilateral gluteal muscles (arrowheads).Figure 6: A 54-year-old woman with lower back pain. (a) Postcontrast sagittal T1-W fat-saturated MR image of the lumbar spine shows a diffusely enhancing lesion in L3 (arrow). (b) CT-guided biopsy of the L3 lesion confirmed the presence of Mycobacterium tuberculosis.Magnetic resonance imaging Magnetic resonance imaging is the imaging of choice for spinal tuberculosis owing to its high sensitivity and specificity.[5] In the early stages, the disease may present with bone marrow signal changes. Abscess formation and subligamentous spread of paraspinal collection with contiguous spinal involvement can also be seen on MRI [Figures 2b, 3b, 3c & 5c]. Although MRI may not allow for definitive identification of the causative microorganism, the pattern of spinal involvement can raise suspicion for tuberculosis. A review of MR images from 40 patients with biopsy-proven spinal tuberculosis or pyogenic spondylodiscitis reported 80% specificity and 90% accuracy of MRI in differentiating spinal tuberculosis from pyogenic infection.[8] Thin, smooth enhancement of the abscess wall and well-defined paraspinal abnormal signal are distinguishing MRI characteristics of spinal tuberculosis [Figure 5d–f].[8] Pyogenic spondylodiscitis, on the other hand, often demonstrates thick, irregular abscess wall enhancement and ill-defined paraspinal abnormal signal [Figure 7].[8] Other indicative features of spinal tuberculosis include subligamentous spread to three or more vertebral levels [Figure 5], involvement of the thoracic spine and multiple vertebral bodies, and the presence of intraosseous abscesses [Figure 3c].[9] Another advantage of MRI is that it allows the assessment of spinal cord and nerve root integrity.[5,7] Spinal cord complications, such as cord oedema, compression, atrophy and syrinx and interstitial gliosis secondary to stretching of the cord, can be detected [Figure 3b].Figure 7: A 53-year-old man with prolonged fever and back pain. Axial T2-W MR image of the lumbar spine shows a collection with thick, irregular walls in the left psoas muscles (arrow). Subsequent imaging-guided drainage of the abscess was positive for Klebsiella pneumoniae.Nuclear medicine imaging The potential role of nuclear medicine imaging in spinal tuberculosis has been explored. Positron emission tomography (PET) has been found to complement MRI in distinguishing spinal tuberculosis from pyogenic spondylodiscitis. A study by Lee et al. reported that maximum standardised uptake values in the early phase on PET differed significantly between the two conditions (P = 0.028), ranging from 2.0–7.1 in spinal tuberculosis and 2.3–8.8 in pyogenic spondylodiscitis.[11] Additionally, PET may be a valuable modality for identifying the most suitable biopsy site for histopathological evaluation and diagnosis.[12]Table 1 shows the key imaging differences between spinal tuberculosis and pyogenic spondylodiscitis.Table 1: Imaging features of spinal tuberculosis and pyogenic spondylodiscitis.SPECIFIC PATTERNS OF DISEASE MANIFESTATION Paradiscal lesion The subchondral region of each vertebra contains an arterial arcade, supplied by the anterior and posterior spinal arteries. This vascular plexus facilities the haematogenous spread of tuberculosis on either side of the disc or the paradiscal region.[5] This can lead to disc space narrowing by destruction of the subchondral bone with subsequent herniation of the disc into the vertebral body or by direct involvement of the disc [Figures 1b & 2b]. Age-related avascularity of the disc makes paradiscal lesions the most common type of presentation in older patients, whereas in younger patients, the disc is primarily involved due to increased vascularity.[5] Anterior element lesion The vertebral body corner adjacent to the endplate is richly vascularised in adults and is a common site for the spread of tuberculosis. The anterior elements are involved when an abscess spreads subperiosteally under the anterior longitudinal ligament. Multiple vertebral segments may be affected, resulting in periosteal and anterior longitudinal ligament stripping. This can present as subligamentous abscesses in the involved vertebra with preservation of the discs [Figure 5c]. The lack of proteolytic enzymes in mycobacterial infections has been suggested as the cause of subligamentous spread of infection.[5] Anterior scalloping may be evident due to a combination of vertebral ischaemia and pressure from the subligamentous flow of abscess.[6] The bifurcation of segmental arteries supplying adjacent vertebrae can further facilitate disease spread to two contiguous vertebral levels. Subsequent progression can result in anterior vertebral collapse and kyphosis [Figure 3]. Central lesion Batson’s paravertebral venous plexus is a valveless system, where the direction of blood flow is dependent on the pressure generated in the intra-abdominal and intrathoracic cavities. The spread of Mycobacterium tuberculosis via the Batson’s venous complex is postulated to be responsible for central vertebral body lesions, where the lesion is centred on the vertebral body without disc involvement [Figure 6a].[5] This can make distinguishing it from metastasis or lymphoma challenging. Posterior element lesions Spinal tuberculosis of the posterior element is rare. The valveless venous plexus is also thought to contribute to posterior element lesions, specifically the pedicles. The thoracic spine is the most common region involved. These posterior element lesions have been associated with severe vertebral body destruction, disc collapse, abscess and kyphosis [Figure 5].[13] Skipped lesions Similar to central and posterior element lesions, the valveless venous plexus likely facilitates the spread of noncontiguous lesions [Figure 3]. Retrograde flow in the valveless venous plexus may allow bacteria to travel from an established spinal focus to new vertebrae without filtration by the lungs or lymphatic system.[14] TREATMENT The diagnosis of spinal tuberculosis is usually made based on a combination of clinical and imaging features to enable early empirical treatment and reduce the risk of complications. A definitive diagnosis of the causative microorganism can be difficult to establish based on clinical and imaging features, and percutaneous spinal biopsy is increasingly being used. Computed tomography-guided biopsy has a detection rate of up to 60%.[15] Antituberculosis treatment is the first line of management for spinal tuberculosis. The World Health Organization recommends a two-phase treatment regimen: a 2-month intensive phase consisting of rifampicin, isoniazid, ethambutol and pyrazinamide and a 4-month continuous phase comprising rifampicin and isoniazid.[3] Surgical intervention is warranted only for selected cases, such as those with neurological deficits, kyphotic deformities or large paravertebral abscesses.[9] CONCLUSION Tuberculosis remains prevalent globally and continues to be encountered clinically and radiologically. Given the potential for high morbidity from spinal tuberculosis, knowledge of its imaging morphology is crucial for early diagnosis, enabling prompt treatment and prevention of irreversible neurological sequelae. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest. SMC CATEGORY 3B CME PROGRAMME Online Quiz: https://www.sma.org.sg/cme-programme Deadline for submission: 6 pm, 22 November 2025