Comparison of MRI, [(18)F]FDG PET/CT, and (99m)Tc-UBI 29-41 scintigraphy for postoperative spondylodiscitis—a prospective multicenter study

PURPOSE: Postoperative infection still constitutes an important complication of spine surgery, and the optimal imaging modality for diagnosing postoperative spine infection has not yet been established. The aim of this prospective multicenter study was to assess the diagnostic performance of three imaging modalities in patients with suspected postoperative spine infection: MRI, [(18)F]FDG PET/CT, and SPECT/CT with (99m)Tc-UBI 29-41. METHODS: Patients had to undergo at least 2 out of the 3 imaging modalities investigated. Sixty-three patients enrolled fulfilled such criteria and were included in the final analysis: 15 patients underwent all 3 imaging modalities, while 48 patients underwent at least 2 imaging modalities (MRI + PET/CT, MRI + SPECT/CT, or PET/CT + SPECT/CT). Final diagnosis of postoperative spinal infection was based either on biopsy or on follow-up for at least 6 months. The MRI, PET/CT, and SPECT/CT scans were read blindly by experts at designated core laboratories. Spine surgery included metallic implants in 46/63 patients (73%); postoperative spine infection was diagnosed in 30/63 patients (48%). RESULTS: Significant discriminants between infection and no infection included fever (P = 0.041), discharge at the wound site (P < 0.0001), and elevated CRP (P = 0.042). There was no difference in the frequency of infection between patients who underwent surgery involving spinal implants versus those who did not. The diagnostic performances of MRI and [(18)F]FDG PET/CT analyzed as independent groups were equivalent, with values of the area under the ROC curve equal to 0.78 (95% CI: 0.64–0.92) and 0.80 (95% CI: 0.64–0.98), respectively. SPECT/CT with (99m)Tc-UBI 29-41 yielded either unacceptably low sensitivity (44%) or unacceptably low specificity (41%) when adopting more or less stringent interpretation criteria. The best diagnostic performance was observed when combining the results of MRI with those of [(18)F]FDG PET/CT, with an area under the ROC curve equal to 0.938 (95% CI: 0.80–1.00). CONCLUSION: [(18)F]FDG PET/CT and MRI both possess equally satisfactory diagnostic performance in patients with suspected postoperative spine infection, the best diagnostic performance being obtained by combining MRI with [(18)F]FDG PET/CT. The diagnostic performance of SPECT/CT with (99m)Tc-UBI 29-41 was suboptimal in the postoperative clinical setting explored with the present study. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00259-020-05109-x.