Radiography
Findings
Conventional radiography is insensitive to the early changes of spondylodiskitis (spondylodiscitis, infectious spondylitis). In the acute setting, radiographs are normal. In the subacute period (1-3 wk), reduced disk-space height and/or endplate erosion may be evident. In the chronic period (>10 wk), vertebral body sclerosis or collapse may be observed on either side of a narrowed disk space. Paraspinal soft tissue opacity may develop. Gradual disk obliteration may occur with fusion (ie, osseous, fibrous). Partial restoration of disk height may be observed with successful treatment.
Degree of Confidence
Plain radiographic findings suggestive of subacute or chronic spondylodiskitis (spondylodiscitis, infectious spondylitis), such as disk-space loss, endplate erosion, and vertebral sclerosis, should be correlated with the patient's clinical history.
False Positives/Negatives
In cases of spondylodiskitis (spondylodiscitis, infectious spondylitis), radiographic findings lag behind clinical response to treatment by approximately 1 month.
Computed Tomography
Findings
In spondylodiskitis (spondylodiscitis, infectious spondylitis), CT scans may appear normal early in the course of disease. Disk-space narrowing or decreased attenuation in the disk is often the earliest manifestation of disease. After the administration of iodinated contrast material, the abnormal disk space, vertebral marrow, or paravertebral soft tissues may enhance.
As the disease progresses, destruction of the vertebral body and fragmentation of vertebral endplates are observed. Destruction may be either diffuse or permeative. The presence of paraspinal soft tissue lesions and/or collections aids in the diagnosis of spondylodiskitis. In children, extrusion of the vertebral body may be observed.14
Degree of Confidence
Overall, CT is more sensitive (68%), more specific (97%), and more accurate (80%) than plain radiography in identifying areas of vertebral osteomyelitis in animal models.
Because of its ease and speed of use, lower cost, and availability, CT is an excellent method for evaluating the bony changes of spondylodiskitis (spondylodiscitis, infectious spondylitis) and for directing radiologic intervention (ie, aspiration or biopsy) in spinal infections. In the diagnosis of active bacterial disk-space infections, the sensitivity and specificity of CT-guided percutaneous aspiration may be as high as 91% and 100%, respectively; however, percutaneous aspiration is less reliable in the diagnosis of nonbacterial infections.
False Positives/Negatives
Gas in the disk space (ie, vacuum phenomenon) may occasionally be observed on CT scans. Although this finding is most often associated with degenerative disk disease, it may also occur with infection.
CT is less sensitive than MRI in depicting soft tissue structures, but its sensitivity may be improved with the use of intravenous contrast material.
Magnetic Resonance Imaging
Findings
MRI is the modality of choice for evaluating spinal infections. In particular, MRI is useful in detecting abnormalities during the acute stage of spinal infection. During the acute stage, MRI may demonstrate increased signal intensity on T2-weighted images in the vertebral body or disk space caused by infarction, abscess, or edema (see Image 2). On T1-weighted images, decreased signal intensity may be observed in the disk and adjacent endplates as a result of edema, and the margin between the disk and the endplate may be diminished.
Paraspinal and epidural abscesses generally appear isointense to muscle on T1-weighted images and hyperintense on fat-saturated T2-weighted or short-tau inversion recovery (STIR) images.
Abscesses of the vertebral body may appear more conspicuous on diffusion-weighted images (DWIs) than on conventional T1- or T2-weighted images.
On contrast-enhanced MRIs, an epidural abscess may appear as an area of peripheral enhancement surrounding an area of fluid signal intensity (see Image 3); it may also appear as an area of abnormal enhancement of disk, vertebral marrow, or paraspinal soft tissue.
The multiplanar capability of MRI allows excellent anatomic localization of the extent of infection, as well as full evaluation of the spinal cord and nerve roots. MRI is also useful for the evaluation of postoperative spinal infections and for the follow-up evaluation of treatment of spondylodiskitis (spondylodiscitis, infectious spondylitis).
Fat-suppression sequences with contrast-enhanced T1-weighted imaging should be routinely performed.15,16,17,18,19,20
Degree of Confidence
MRI is 96% sensitive, 92% specific, and 94% accurate in the evaluation of spondylodiskitis (spondylodiscitis, infectious spondylitis).
False Positives/Negatives
Signal and enhancement changes may persist after clinical resolution of the infection; such findings gradually decrease over weeks to months. This illustrates the fact that contrast enhancement is not always indicative of active infection. These changes do not occur as rapidly as with gallium scanning.
False-negative findings may occur in patients with spondylodiskitis (spondylodiscitis, infectious spondylitis) caused by organisms of low virulence (eg, diphtheroids, coagulase-negative staphylococci).
Ultrasonography
Findings
The usefulness of ultrasound is limited in spondylodiskitis (spondylodiscitis, infectious spondylitis). Occasionally, ultrasonography may be useful for localizing large paraspinal fluid collections for purposes of aspiration and/or drainage. Color Doppler sonography may show areas of hyperemia surrounding abscesses.
Nuclear Imaging
Findings
Radionuclide studies are useful for early detection (3-15 d) of spinal infection. However, establishing this diagnosis may be more difficult in the spine than in other areas of the skeleton because of the presence of active bone marrow.
On 3-phase technetium-99m (99m Tc) scintigraphy, osteomyelitis is characterized by nonspecific arterial hyperemia and the progressive focal skeletal uptake of tracer.
Bone scan specificity may be increased by combining99m Tc with an indium-111–labeled WBC or gallium-67 (67 Ga) scans.67 Ga functions as an acute-phase reactant, accumulating in areas of inflammation.111 In-labeled WBCs also accumulate in areas of infection and inflammation. Areas of infection should appear hotter on the67 Ga scan than on the accompanying99m Tc scan. Infective lesions may appear hot or cold on111 In WBC scans.67 Ga scans may normalize after satisfactory treatment, and they may be used to monitor treatment response.
The use of single-photon emission CT enhances the 3-dimensional localization of infection.21,22
Degree of Confidence
The degrees of confidence of the aforementioned scans is as follows:
Open table in new window
Table
| Scan | Sensitivity (%) | Specificity (%) | Accuracy (%) |
|---|---|---|---|
| 67 Ga | 89 | 85 | 86 |
| 111 In WBC | 17 | 100 | 31 |
| 99m Tc | 90 | 78 | 86 |
| Combined111 In WBC and99m Tc | 90 | 91 | Not available |
| Combined67 Ga and99m Tc | 90 | 100 | 94 |
| Scan | Sensitivity (%) | Specificity (%) | Accuracy (%) |
|---|---|---|---|
| 67 Ga | 89 | 85 | 86 |
| 111 In WBC | 17 | 100 | 31 |
| 99m Tc | 90 | 78 | 86 |
| Combined111 In WBC and99m Tc | 90 | 91 | Not available |
| Combined67 Ga and99m Tc | 90 | 100 | 94 |
False Positives/Negatives
Nuclear scintigraphy is sensitive for vertebral osteomyelitis; however, increased bone turnover from surgery, fracture, or degenerative changes decreases specificity.
False-negative results may occur when atherosclerosis or primary bone destruction compromises blood flow to a lesion.
Use of111 In WBCs may increase the specificity of bone scanning; however, the images may be falsely negative in patients with chronic osteomyelitis or falsely positive in patients with inflammatory or reactive conditions such as rheumatoid arthritis and fractures.
Angiography
Findings
Angiography has no practical role in the diagnosis of spine infection.
More on Spondylodiskitis |
| Overview: Spondylodiskitis |
 Imaging: Spondylodiskitis |
| Follow-up: Spondylodiskitis |
| Multimedia: Spondylodiskitis |
| References |
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Further Reading
Keywords
spondylodiskitis, spondylodiscitis, infectious spondylitis, infective spondylitis, osteomyelitis, vertebral osteomyelitis with discitis, IS, intravenous drug abuse, IVDA
