Objective: The aim of this study was to investigate whether diffuse increased splenic fluorodeoxyglucose (FDG) uptake may be an indirect sign of an acute pyogenic cause of infectious spondylitis (IS).
Methods: A retrospective review identified consecutive records of patients with IS who underwent F-18 FDG positron emission tomography-computed tomography scans between January 2007 and July 2008 and recruited 23 patients (57.8 ± 15.6 years, range: 20-81 years, eight men, 15 women) and their hematological laboratory data. The regions of interest were used to measure the maximum standardized uptake value (SUVmax) for the bone marrow (BM), liver, and spleen in each patient. We calculated the spleen/liver ratio (S/L ratio) by dividing the spleen SUVmax by liver SUVmax and the spleen/BM ratio (S/B ratio) by dividing spleen SUVmax by BM SUVmax as a parameter to assess the splenic FDG uptake.
Results: The acute pyogenic cause of the IS group showed statistically significantly higher values of spleen SUVmax (median, 1.71 vs. 1.16, P=0.0108), S/L ratio (median, 1.08 vs. 0.88, P=0.0454), and S/B ratio (median, 1.30 vs. 0.94, P=0.0055) than the chronic tuberculous cause of the IS. The optimal cut-off values for the quantitative indices were spleen SUVmax>1.49, S/B ratio>0.957, and S/L ratio>0.889.
Conclusion: On the basis of the results presented, this study demonstrated that some quantitative indices from F-18 FDG positron emission tomography/computed tomography images could be indirect signs of an acute pyogenic cause of the IS. Among the various quantitative indices, spleen SUVmax, S/B ratio, and S/L ratio were potent indicators for an acute pyogenic cause of the IS.