Utility of magnetic resonance imaging in the differential diagnosis of tubercular and pyogenic spondylodiscitis

Abstract

Aim: We evaluated the potential of magnetic resonance imaging (MRI) in the diagnosis of spinal infections and specifically its accuracy in differentiating tubercular and pyogenic spondylodiscitis.

Materials and methods: Totally, 50 patients referred for MRI scans with the clinical diagnosis of spinal infections were included in our study. The patients were classified as tubercular (TS), pyogenic (PS), and indeterminate spondylodiscitis on the basis of imaging findings and were correlated with the final diagnosis made by histopathology/cytology/culture/biochemistry or with successful therapeutic outcome. Imaging findings were subsequently analyzed for differentiating tubercular and pyogenic spondylodiscitis using the Chi-square test.

Results: The most common pattern of spinal infection was spondylodiscitis (78% incidence rate) with epidural extension (86%) and cord compression (64%) being most common complications observed. Imaging (postcontrast study) and final diagnosis correlated in 93.7% tubercular (sensitivity of 75% and specificity of 90%) and 75% pyogenic (sensitivity of 90% and specificity of 83.3%) spondylodiscitis. The patients with tubercular spondylitis had a significantly (P < 0.05) higher incidence of following MRI findings: A well-defined paraspinal abnormal signal (80% in TS vs. 40% in PS), a thin and smooth abscess wall (84.2% in TS vs. 10% in PS), presence of intraosseous abscess (35% in TS vs. 0% in PS), focal and heterogenous enhancement of the vertebral body (75% in TS vs. 20% in PS), vertebral destruction more than or equal to grade 3 (71.8% in TS vs. 0% in PS), loss of cortical definition (75% in TS vs. 20% in PS), and spinal deformity (50% in TS vs. 5% in PS).

Conclusion: Contrast-enhanced images improve the sensitivity and specificity of detection and differentiation of tubercular and PS.

Keywords: Cortical destruction; magnetic resonance imaging; spondylitis.

Figure 1

Tubercular Spondylodiscitis — Sagittal T1, T2 and STIR images show anterior wedging of C6 and C7 vertebral bodies. Disc at C6-7 level is inappreciable on T1 and T2W images. Subligamentous spread (from C5-D2) and anterior epidural soft tissue(C5-7) is seen

Figure 2

Pyogenic spondylodiscitis — Sagittal T1, T2 and STIR images: Areas of altered signal intensity appearing iso intense on T1, mildly hyperintense on T2/STIR images are seen involving L1-2 and L4-5 vertebrae. Intervening discs show hyperintense signal on T2W images with bright disc sign s/o discitis. Patient had a pus discharging wound in lumbar region, culture revealed E. coli.

Figure 3

Intraosseous abscesses in tubercular spondylitis — Spondylitis without discitis: T1 post contrast saggital images show heterogenous enhancement of the D11-L1 vertebare with intraosseous abscesses. Intervertebral discs are normal

Figure 4

Isolated epidural abscesses: Pyogenic infection — T2 sagittal images before and after L1-3 laminectomy. A: Posterior epidural soft tissue is seen at D12-L3 level causing compression of the lower dorsal cord with cord edema. B: After laminectomy and drainage of pus no collection is seen. Pus culture revealed growth of gram positive cocci

Figure 5

Isolated infective facetal arthropathy: Pyogenic — T2 axial images show left facet joint space at L4-5 and L5-S1 are widened with fluid signal intensity in them. Small loculated collections are seen in posterior paraspianl muscles

Figure 6

Disseminated tuberculosis — Multifocal involvement is seen in the form of intraparenchymal granulomas, multilevel spondylodiscitis, tiny vertebral granuloms and nodular lung lesions

Figure 7

Tubercular spondylodiscitis with intramedullary granulomas and myelopathy — T2W images show hyperintense signal involving the dorsal cord s/o myelitis. Intramedullary rim enhancing granulomas are seen with spondylodiscitis at C5-6 level

Figure 8

Pyogenic spondylodiscitis — Images show complete disc destruction with discal abscesses at C2-3, C3-4 and C4-5 levels and grade 1 destruction of vertebral bodies. Bones of the skull base show heterogenous enhancement. The paraspinal signal is ill defined. The abscess wall is thick and irregular