“…Some investigators consider it to be part of IgG4-Related Disease (IgG4-RD) because of its association with many auto-immune disorders (Zhang et al, 2017, Hedgire et al, 2013, Khosroshahi et al, 2013, Subramani et al, 2019. As retroperitoneal fibrosis can be secondary to chemoradiation for another malignancy, it is essential to differentiate between primary or secondary RPF (Murakami et al, 2018). The diagnosis is made on the basis of Computed Tomography (CT) or Magnetic Resonance Imaging (MRI), while Fluorodeoxyglucose Positron emission tomography ([18F] FDG PET) is a useful tool in disease staging and follow-up (Vaglio & Moriatati, 2016;Carmel et al, 2008, Caiafa et al, 2013.…”