Applied Radiology

Findings

X-rays of the dorsal spine showed no obvious lytic vertebral lesions, and the intervertebral disc spaces were normal. General coarsening and fuzziness of the trabecular pattern was noted, however, with associated widening of the left paraspinal shadow (Figure 1). The chest radiograph showed no pulmonary parenchymal abnormality (Figure 2). The patient was further examined, and a CT scan of the dorsal spine showed multiple osteolyticsclerotic lesions involving multiple dorsal vertebrae with associated small paraspinal soft tissue masses (Figure 3, A and B). In view of the widespread nature of the lesions in the dorsal spine, scanning was extended to cover the cervical and lumbosacral regions. Similar lesions were noted involving the bodies and posterior elements of all the cervical, dorsal, and lumbar vertebrae and sacrum, with minimal associated enhancing soft tissue. The intervertebral discs were characteristically spared, and the epidural space and thecal sac were normal (Figure 3, C and D). Lytic lesions involving the ribs and the sternum were also seen, and a skeletal survey revealed an additional lytic focus in the left iliac bone (Figure 4). In view of the extensive involvement of the spine lytic lesions in the ribs, sternum, and left iliac bone and because of selective sparing of intervertebral discs, the possibility of an infiltrative bone disorder was suggested. The bone marrow aspiration study was normal, however, and an open biopsy taken from the dorsal spinal column yielded caseous material with isolation of acid-fast bacilli from the sample.

As the patient improved on antitubercular treatment, no surgical procedure was contemplated. A repeat CT scan showed significant healing and resolution of the lytic lesions and the paraspinous soft tissue masses.

Discussion

Spinal tuberculosis, the most common form of skeletal involvement in tuberculosis, is usually the result of hematogenous seeding of the vertebral body, and the diagnosis often remains elusive because of the indolent nature of the infection.¹ As a result, the radiographic findings and the signs and symptoms are typically far advanced when the diagnosis is finally established.

Spinal tuberculosis can be broadly classified into the following types: a) vertebral body-isolated (solitary); b) vertebral body with adjacent disc; c) posterior element tuberculosis; d) subligamentous tuberculosis; e) multifocal tuberculosis; f) atlantoaxial tuberculosis; g) epidural tuberculosis; h) tuberculous arachnoiditis/ meningeal tuberculosis; i) intramedullary tuberculosis; and j) sacral/sacroiliac joint tuberculosis.

Spinal tuberculosis classically begins in the anterior inferior portion of a vertebral body. The infection spreads beneath the anterior longitudinal ligament to involve adjacent vertebral bodies. Disc space narrowing is a secondary phenomenon, occurring when destruction of the cancellous bone permits herniation of the disc into the affected vertebral body.

Radiographic manifestations of tuberculous spondylitis include destroyed vertebrae with associated intraosseous and paraspinal abscess formation, subligamentous spread of infection, extension into the spinal epidural space, vertebral body collapse, and focal gibbus formation. Involvement of a single vertebra is a relatively common finding.² Large psoas abscesses can occur without any signs of bone involvement.

CT appearances of bone destruction are highly suggestive of tuberculous osteomyelitis in about half of the patients with this condition. Four patterns of bone destruction are noted: fragmentary, osteolytic, subperiosteal, and well-defined lytic with sclerotic margins. The fragmentary type is the most common (47%). Intervertebral disc destruction is always associated with contiguous vertebral body destruction.³ MR imaging is useful to determine the spread of disease to the soft tissues and the spinal canal.

The classic radiologic picture of "2 vertebral diseases that cause destruction of the intervertebral disc" is easily recognized and readily treated, but its atypical forms are often misdiagnosed and mistreated.⁴ The infective process can sometimes be indistinguishable from malignant processes, and with multiple lesions in the spine, it can mimic metastatic disease.

The involvement of multiple contiguous vertebrae in spinal tuberculosis is well documented. However, in all such cases, the invariable involvement of intervertebral disc spaces has been seen. In our case, selective sparing of intervertebral disc spaces was seen in spite of extensive involvement of multiple contiguous vertebrae. The largest number of radiologically involved vertebrae so far has been 10 contiguous dorsal vertebrae in 4 patients over a period of 30 years of observation.⁵ Less than 2% of all spinal lesions in tuberculosis show radiologically intact spaces-usually the anterior subperiosteal, appendiceal, and central lytic type of lesions.⁶ Additional atypical features seen in our patient were the presence of small paraspinal masses relative to the extent of vertebral destruction, no spinal deformity, and good general condition of the patient. This atypical variety of tuberculous spondyltis has been called the "pseudotumor" appearance with multilevel vertebral involvement and normal intervening discs.⁷ Biopsy is commonly required to differentiate between neoplasm and infection.

Pott's disease of the spine may mimic other disease processes, and thus a definite list of differential diagnosis should be kept in mind before proceeding with specific treatment. The following lesions should be considered and ruled out-atypical mycobacterial or nontuberculous infections-pyogenic, fungal, hydatid, etc., metastasis, primary bone tumors (aneurysmal bone cyst, giant cell tumors, chordomas, plasma cell tumors, myelomas, etc.).

CONCLUSION

The most conclusive means of reaching the diagnosis (biopsy and culture) necessitate invasive procedures that are not always definitive and may require repeated attempts. When diagnosing tuberculosis, physicians should include Pott's disease in the differential diagnosis when radiologic findings suggest spinal infections or a primary/secondary spinal neoplastic process.

1. Shanley DJ. Tuberculosis of the spine: Imaging features. AJR Am J Roentgenol.1995;164:659-664.
2. Lindahl S, Nyman RS, Brismar J, et al. Imaging of tuberculosis. IV. Spinal manifestations in 63 patients.Acta Radiol.1996;37:506-511.
3. Jain R, Sawhney S, Berry M. Computed tomography of vertebral tuberculosis: Patterns of bone destruction.Clin Radiol.1993;47:196-199.
4. Narlawar RS, Shah JR, Pimple MK, et al. Isolated tuberculosis of posterior elements of spine: Magnetic resonance imaging findings in 33 patients.Spine.2002;27:275-281.
5. Turgut M.Multifocal extensive spinal tuberculosis (Pott's disease) involving cervical, thoracic and lumbar vertebrae. Br J Neurosurg.2001;15:142-146.
6. Tuli SM.Tuberculosis of the Skeletal System:Bones, Joints, Spine and Bursal Sheaths .2nd ed. New Delhi, India: Jaypee Brothers Publishers; 1997:183.
7. Smith AS, Weinstein MA, Mizushima A, et al. MR imaging characteristics of tuberculous spondylitis vs vertebral osteomyelitis. AJR Am J Roentgenol.1989;153:399-405.