A comparison between magnetic resonance imaging and scintigraphic bone imaging in the diagnosis of disc space infection in an animal model.

In a controlled prospective study, 33 rabbits were used to compare the efficacy of magnetic resonance imaging (MRI) to scintigraphy in diagnosing pyogenic infection of the intervertebral disc. A suitable inoculum of Staphylococcus aureus (10(8) organisms) was injected into a test level while a similar volume of sterile culture medium was injected into a control disc in each animal. Plain radiographs, MRI, and scintigraphic bone images then were performed at regular intervals after operation. The imaging studies were interpreted blind, as was the final histologic assessment. Five animals died of respiratory complications following sedation. In the remaining 28 animals, 23 developed infection at the test level, and four developed infection at the control disc. Magnetic resonance imaging was found to be more sensitive than scintigraphy in diagnosing discitis, particularly in the early stages of the disease. The overall results showed MRI had a sensitivity of 93%, specificity of 97%, and accuracy of 95%. There were two false-negative results and one false-positive. In contrast, scintigraphy had a sensitivity of 41%, specificity of 93%, and accuracy of 68%. There were two false-positive and 16 false-negative results. Plain radiographs had a sensitivity of 82%, specificity of 93%, and accuracy of 88%. There were two false-positive and five false-negative results. The MRI appearance of discitis was characteristic from an early stage in the disease, and preceded the changes on scintigraphy and plain radiographs by several days in the majority of cases.