The aim of this article was to critically assess the usefulness of hybrid molecular imaging (FDG PET/CT and FDG PET/MR) procedures in the evaluation of inflammatory activity in retroperitoneal fibrosis (RPF). A systematic review of the literature was performed using PubMed without timeline restriction and using the following keywords: retroperitoneal fibrosis, disease activity, diagnostic techniques, PET/CT, PET/MR. We evaluated full text articles written in the English language. Case reports, review articles or editorials and articles not in the field of interest of this review were excluded. Nine articles comprising a total of 186 patients met the inclusion criteria and were included and described in this systematic review. The new hybrid molecular imaging methods give promising results in the evaluation of the activity of the disease, quantification and prediction of therapeutic response and in tailoring medical therapy in RPF. FDG PET/CT can be a valuable tool in detecting disease activity, particularly in asymptomatic patients with RPF with acute phase reactant increase. Hybrid imaging can predict therapy response outcome and the best time for stent removal. Although PET/MR has potential advantage in small lesions and has reduced radiation exposure in comparison to PET/CT, PET quantification parameters have potentially higher diagnostic value over MR parameters in the evaluation of RPF. Acute phase reactants alone may not be reliable for the management and follow-up assessment of the disease. Hybrid imaging in RFP could be more comfortable, more accurate, with less radiation burden than different separate imaging studies acquired at different points in time.
Keywords: FDG PET/CT; FDG PET/MR; Imaging techniques; Inflammatory activity assessment; Retroperitoneal fibrosis.