18F-FDG PET/CTand Radiolabeled Leukocyte Scintigraphy for the Diagnosis of Infected Aortic Aneurysms: a retrospective study

543 Introduction: Infectious aortitis is a rare but potentially life-threatening disorder. Prompt diagnosis is crucial, with mortality rates of up to 44% despite treatment. The incremental diagnostic value of 18F-FDG PET/CT and radiolabeled leukocyte scintigraphy (RLS) has already been reported in endocarditis. The aim of this study was to compare the respective performance of 18F-FDG PET/CT and RLS for the diagnosis of infected aortic aneurysm (IAA). Materials and Methods: Between september 2016 and march 2018, eighteen patients were enrolled retrospectively with suspected IAA diagnosed on the basis of a combination of symptoms or CTA findings and underwent 18F-FDG PET/CT and RLS. The results of 18F-FDG PET/CT and RLS were analyzed separately by experienced physicians masked to the results of the other imaging technique and to patient outcome. Final diagnosis of IAA was established based either on the bacteriological analyses of excised tissues or by experienced infectious disease specialists and vascular surgeons. Results: Of the 23 sites, 12 were classified as infected. Sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 92%, 91%, 92%, 83% and 91% for 18F-FDG PET/CT and 75%, 100%, 100%, 79% and 87% for RLS respectively. Discrepancies between the results of 18F-FDG PET/CT and RLS occurred in 5 patients (22%). In patients with IAA, 3 had true positive 18F-FDG PET/CT results (Coxiella Burnetti, Yersinia Enterolitica and Streptococcus Pneumoniae) and 1 had true positive RLS results (Coxiella Burnetti). The last patient with a discrepancy (non-IAA) had false positive 18F-FDG PET/CT. In PET/CT, for the semi-quantitative analysis, the median aortic wall TBRmax was significantly higher 3.96 (3.27-5.48) in patients with IAA versus 1.63 (1.40-2.20) in patients without IAA (p=0.02). Conclusions: 18F-FDG PET/CT offers higher sensitivity while RLS offers higher specificity for the detection of active infection in patients with suspected infectious aortic aneurysms.18F-FDG PET/CT is relevant as first-line molecular imaging when IAA is suspected. A sequential strategy consisting of 18F-FDG PET/CT imaging followed by RLS in the event of positive 18F-FDG PET/CT results without obvious bacteriological data or negative 18F-FDG PET/CT results with pejorative clinical course may be of relevance.