Value of ¹⁸ F-FDG PET/CT to identify occult infection in presumed aseptic pseudarthrosis after spinal fusion: correlation with intraoperative cultures

Fluorine-18 fluorodeoxyglucose (¹⁸ F-FDG) positron emission tomography/ computed tomography (PET/CT) has gained attention as an emerging tool in case of suspicion of infection on spine, whether native or instrumented. The PET/CT images were analyzed in consensus by two nuclear medicine physicians blinded to the clinical, biological, and imaging information.Thirty-six presumed aseptic patients with surgically confirmed pseudarthrosis after spinal fusion underwent preoperative ¹⁸ F-FDG PET/CTscans. Cultures of samples from revisions found that 20 patients (56%) were infected. The most frequent isolated bacterium was Cutibacterium acnes (C. acnes) in 15 patients (75%), followed by coagulase-negative staphylococci (CNS) in 7 patients (33%). Two patients had co-infections involving both C. acnes and CNS. Of the 36 PET/CT studied in this study, 12 scans were true-negative, 10 true-positive, 10 false-negative, and 4 false-positive. This resulted in sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of 50%, 75%, 71%, 55%, and 61%, respectively. In presumed aseptic pseudarthrosis after spinal fusion, ¹⁸ F-FDG PET/CT offers good specificity (75%) but low sensitivity (50%) to identify occult SSI. The high prevalence (56%) of SSI, mostly caused by C. acnes (75%), found in our presumed aseptic cohort of patients supports the utility of systematic intraoperative cultures in revision cases for pseudarthrosis