How to combine CTA, 99mTc-WBC SPECT/CT, and [18F]FDG PET/CT in patients with suspected abdominal vascular endograft infections?
Chiara Lauri, Giuseppe Campagna, Francesco Aloisi, Alessandro Posa, Roberto Iezzi, Pasqualino Sirignano, Maurizio Taurino, Alberto Signore
Abstract
Abstract Purpose We aimed at comparing 99m Tc-HMPAO white blood cells ( 99m Tc-WBC) scintigraphy, 18fluorine-fluorodeoxyglucose ([ 18 F]FDG) positron emission tomography/computed tomography (PET/CT) and CT angiography (CTA) in patients with suspected abdominal vascular graft or endograft infection (VGEI). Moreover, we attempted to define a new visual score for interpreting [ 18 F]FDG PET/CT scans aiming at increasing its specificity. Methods We prospectively compared 99m Tc-WBC SPECT/CT, [ 18 F]FDG PET/CT, and CTA in 26 patients with suspected abdominal VGEI. WBC scans were performed and interpreted according to EANM recommendations. [ 18 F]FDG PET/CT studies were assessed with both qualitative (Sah’s scale and new visual score) and semi-quantitative analyses. CTA images were interpreted according to MAGIC criteria. Microbiology, histopathology or a clinical follow-up of at least 24 months were used to achieve final diagnosis. Results Eleven out of 26 patients were infected. [ 18 F]FDG PET/CT showed 100% sensitivity and NPV, with both scoring systems, thus representing an efficient tool to rule out the infection. The use of a more detailed scoring system provided statistically higher specificity compared to the previous Sah’s scale ( p = 0.049). 99m Tc-WBC SPECT/CT provided statistically higher specificity and PPV than [ 18 F]FDG PET/CT, regardless the interpretation criteria used and it can be, therefore, used in early post-surgical phases or to confirm or rule out a PET/CT finding. Conclusions After CTA, patients with suspected late VGEI should perform a [ 18 F]FDG PET/CT given its high sensitivity and NPV. However, given its lower specificity, positive results should be confirmed with 99m Tc-WBC scintigraphy. The use of a more detailed scoring system reduces the number of 99m Tc-WBC scans needed after [ 18 F]FDG PET/CT. Nevertheless, in suspected infections within 4 months from surgery, 99m Tc-WBC SPECT/CT should be performed as second exam, due to its high accuracy in differentiating sterile inflammation from infection.