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1 Department of Diagnostic Radiology, Kangnam St. Mary's Hospital, The Catholic
University of Korea, 505 Banpodong, Seocho-ku, Seoul 137-040, Korea.
2 Department of Orthopedic Surgery, Kangnam St. Mary's Hospital, The Catholic
University of Korea, Seoul, Korea.
3 Department of Neurosurgery, Kangnam St. Mary's Hospital, The Catholic
University of Korea. Seoul, Korea.
Received October 29, 2003;
accepted after revision November 20, 2003.
Address correspondence to W.-H. Jee
(whjee{at}catholic.ac.kr).
Abstract
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MATERIALS AND METHODS. MR images of 52 patients who had MRI of the spine and confirmed spondylitis were retrospectively reviewed. After review of medical records, we compared MRI findings in 20 patients with tuberculous spondylitis and 20 patients with pyogenic spondylitis. Statistical analysis was performed with the chi-square test.
RESULTS. The reviewer identified tuberculous spondylitis with sensitivity, specificity, and accuracy of 100% (20/20), 80% (16/20), and 90% (36/40), and pyogenic spondylitis with sensitivity, specificity, and accuracy of 80% (16/20), 100% (20/20), and 90% (36/40), respectively. The patients with tuberculous spondylitis had a significantly higher incidence of MRI findings as follows (p < 0.05): a well-defined paraspinal abnormal signal (95% [19/20] in tuberculous vs 25% [5/20] in pyogenic), a thin and smooth abscess wall (95% [19/20] vs 15% [3/20]), combination of both findings (90% [18/20] vs 0% [0/20]), presence of paraspinal or intraosseous abscess (95% [19/20] vs 50% [10/20]), subligamentous spread to three or more vertebral levels (85% [17/20] vs 40% [8/20]), involvement of multiple vertebral bodies (60% [12/20] vs 25% [5/20]), thoracic spine involvement (40% [8/20] vs 10% [2/20]), and hyperintense signal on T2-weighted images (95% [19/20] vs 65% [13/20]).
CONCLUSION. MRI was accurate for differentiation of tuberculous spondylitis from pyogenic spondylitis.
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The purpose of this study was to determine the accuracy of MRI in discriminating between tuberculous spondylitis and pyogenic spondylitis.
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MRI was performed on 1.5-T imagers (Signa, General Electric Medical Systems) in 19 patients and (Magnetom Vision, Siemens) in 21 patients, using a surface coil or spine coil. Axial and sagittal T1-weighted MR images (TR range/TE range, 350–650/11–30) and fast spin-echo or turbo spin-echo T2-weighted images (3,000–4,000/76–108) were obtained. In addition, axial and sagittal fat-suppressed T1-weighted images (350–800/11–30) were obtained after IV infusion of 0.1 mmol/kg of gadopentetate dimeglumine. Typical MR parameters were as follows: field of view, 15–20 cm for axial plane and 30–35 cm for sagittal plane; number of excitations, 2; matrix size, 256 x 192; slice thickness, 4 mm; intersection gap, 1 mm; and echo-train length, 8–16.
The reviewer evaluated the presence or absence of individual imaging criteria and made an overall assessment of the type of spondylitis. The margin of paraspinal abnormal signal, the appearance of the abscess walls, the extent of subligamentous spread, horizontal bandlike sparing of the body, involvement of multiple vertebral bodies, the involvement of the thoracic spine, entire body involvement, and the signal intensity of involved vertebral bodies were evaluated. The abscess wall was assessed by the reviewer on the basis of the contrast-enhanced images. The signal intensity in the marrow of abnormal vertebrae was considered hypointense, isointense, or hyperintense by comparison with the signal intensity of normal vertebrae in the same patient on T1- and T2-weighted images. Statistical analysis was performed with the chi-square test.
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The incidence of the following MRI findings was significantly higher in patients with tuberculous spondylitis than in those with pyogenic spondylitis (p < 0.05): a well-defined paraspinal abnormal signal (95% in tuberculous vs 25% in pyogenic) (Fig. 3A, 3B, 3C, 3D), a thin and smooth abscess wall (95% vs 15%), combination of both findings (90% vs 0%), presence of paraspinal or intraosseous abscess (95% vs 50%), subligamentous spread or more three vertebral levels (85% vs 40%), involvement of multiple vertebral bodies (60% vs 25%), and thoracic spine involvement (40% vs 10%).
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The incidence of the following MRI findings was significantly higher in patients with pyogenic spondylitis than in those with tuberculous spondylitis (p < 0.05): an ill-defined paraspinal abnormal signal (70% in pyogenic vs 5% in tuberculous) (Fig. 4A, 4B, 4C, 4D), absence of paraspinal or intraosseous abscess (50% vs 5%), subligamentous spread to fewer than three vertebral levels or without subligamentous spread (60% vs 15%), a thick and irregular abscess wall (35% vs 0%), a horizontal bandlike sparing of the body (25% vs 0%), and involvement of two or fewer vertebral bodies (75% vs 40%).
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All patients with spondylitis showed a hypointense to isointense signal on T1-weighted images. No significant difference in heterogeneous signal was seen on T1-weighted images (100% in tuberculous vs 85% in pyogenic, p = 0.115) or high signal foci on T1-weighted images (20% vs 10%, p = 0.331). Hyperintense signal on T2-weighted images was more commonly observed in tuberculous spondylitis (95% in tuberculous vs 65% in pyogenic, p < 0.05), whereas isointense signal on T2-weighted images was more commonly observed in pyogenic spondylitis (35% in pyogenic vs 0% in tuberculous, p = 0.004). No significant difference in hypointense signal was seen on T2-weighted images (5% in tuberculous vs 0% in pyogenic, p = 0. 500) or heterogenous signal on T2-weighted images (100% vs 95%, p = 0.500). Contrast enhancement pattern showed no significant difference in either the heterogeneous pattern (100 in tuberculous vs 80% in pyogenic, p = 0.053) or the homogeneous pattern (0% vs 20%, p = 0.053).
In tuberculous spondylitis, thoracic or thoracolumbar involvement was observed in 40% of cases and lumbar involvement in 50% of cases, whereas in pyogenic spondylitis, thoracic involvement was observed in 10% of cases and lumbar involvement was observed in 70% of cases. The involvement of the posterior element (90% in tuberculous vs 70% in pyogenic, p = 0.118) and epidural extension (100% vs 90%, p = 0.244) were not significantly different in tuberculous and pyogenic spondylitis. No difference was present in the involvement of intervertebral disk (80% in tuberculous vs 90% in pyogenic, p = 0.171) and disk space narrowing (55% in tuberculous vs 45% in pyogenic, p = 0.376).
The longest contiguous involvement of the spine in tuberculous spondylitis was associated with five vertebral bodies. One patient with tuberculous spondylitis had a skip lesion involving the thoracic and lumbar spine independently, and in one patient the tuberculous spondylitis involved only one vertebral body.
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Differentiation between tuberculous and pyogenic spondylitis is difficult clinically and radiographically. MRI has been reported to be useful in the early detection of spondylitis [2, 6–8]. To our knowledge, there have been a few reports [2, 9, 10] on differential MRI findings between tuberculous spondylitis and pyogenic spondylitis.
Rim enhancement of abscess on MRI is reportedly suggestive of tuberculous spondylitis [1, 2, 4, 7, 10]. However, rim enhancement was observed in both tuberculous and pyogenic spondylitis in this study. The two most reliable MRI findings suggesting tuberculous spondylitis in our study were thin and smooth enhancement of the abscess wall and well-defined paraspinal abnormal signal, whereas thick and irregular enhancement of abscess wall and ill-defined paraspinal abnormal signal were suggestive of pyogenic spondylitis. Thus, contrast-enhanced MRI was essential in the differentiation of these two types of spondylitis. Hong et al. [11] reported that in tuberculous arthritis the margins of extraarticular lesions were smoother and the abscess walls were thinner and smoother than in pyogenic arthritis. Regarding the margin of the soft-tissue abnormal signal and the appearance of the abscess wall, tuberculous and pyogenic spondylitis presented MRI findings similar to those of tuberculous and pyogenic arthritis, respectively. We assumed that the relative late phase and chronic course of tuberculous spondylitis contributed to the smoother margin of the paraspinal abnormal signal and a thinner and smoother abscess wall. The minimal inflammation of tuberculous abscess may also contribute to the thin and smooth appearance of abscess wall.
It was recently reported that signal intensity was of limited value in differentiating tuberculous arthritis from pyogenic arthritis [11]. In contrast, in this study hyperintense signal on T2-weighted images were more common in tuberculous spondylitis than in pyogenic spondylitis. This discrepancy between the studies could be due to the use of various MRI units in the previous study, whereas only 1.5-T scanners at one institution were used in this study.
A lack of proteolytic enzymes in the Mycobacterium as compared with pyogenic infection has been proposed as the cause of relative preservation of the intervertebral disks [2, 9, 12]. However, in this study, disk space narrowing was observed in 55% (11/20) of the patients with tuberculous spondylitis, which was similar to that for 45% (9/20) of the patients with pyogenic spondylitis. We assumed that a longer interval existed from presentation to MRI in tuberculous spondylitis than pyogenic spondylitis in our study. Disk space narrowing was prominent in 72% (21/29) of patients with tuberculous spondylitis in the study by Liu et al. [13].
Subligamentous spread to three or more vertebral levels was frequent in tuberculous spondylitis in our study, which is consistent with previous reports [8, 10]. The involvement of the thoracic spine and multiple vertebral bodies was significantly higher in our patients with tuberculous spondylitis than in patients with pyogenic spondylitis, which is also consistent with previous reports [5, 14]. Horizontal bandlike sparing of the body was exclusively observed in 25% of cases of pyogenic spondylitis, although it was observed in a minority of the patients with pyogenic spondylitis. In contrast to previous reports [5, 7], lumbar involvement was as common as thoracic and thoracolumbar involvement in our patients with tuberculous spondylitis. We assume that lumbar involvement of tuberculous spondylitis probably is not as uncommon as considered previously. Involvement of the posterior element has been reported in tuberculous spondylitis and very uncommonly in pyogenic spondylitis [2, 4, 9]. According to a recent report [15], posterior element tuberculosis is not as rare (at 24%) as previously reported. In our study, abnormal signal of the posterior element was observed in 90% of patients with tuberculous spondylitis and in 70% of patients with pyogenic spondylitis, but this difference was not significant. We consider that more common abnormal signals of the posterior element in this study could be related to the use of fat-suppressed contrast-enhanced T1-weighted images with 1.5-T MR scanners. Skip lesions have been reported as suggestive MRI findings of tuberculous spondylitis [1, 2, 7, 14, 15], and such a lesion was observed in one patient with tuberculous spondylitis in this study.
Several limitations are associated with the study reported here. MR images were interpreted by only one experienced musculoskeletal radiologist. Thus, interobserver variability and accuracy associated with less experienced radiologists was not assessed. The sample sizes were small. The reviewer knew that all cases of spondylitis were either tuberculous or pyogenic, which may have increased the sensitivity of the MRI diagnosis for both conditions. The time-of-presentation factor may influence the margin of paraspinal abnormal signal and the appearance of abscess wall; therefore, a better study would be to compare same time to clinical presentation cases.
In conclusion, MRI was accurate for differentiation of tuberculous spondylitis from pyogenic spondylitis. A well-defined paraspinal abnormal signal, a thin and smooth abscess wall, subligamentous spread to three or more vertebral levels, and multiple vertebral or entire body involvement were more suggestive of tuberculous spondylitis than pyogenic spondylitis.
Acknowledgments
We thank Thomas R. McCauley for his review of the manuscript.
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