gms | German Medical Science

Purpose: Idiopathic retroperitoneal fibrosis (IRF) is a rare inflammatory condition potentially leading to severe complications such as renal failure. Besides, there is evidence of associated large vessel vasculitis (LVV), potentially causing life-threatening consequences such as vessel stenosis and aneurysms. Therefore, early and precise assessment of both disease extent and activity is essential to guide therapy decision. Due to the lack of reliable parameters to objectively assess the degree of inflammation, imaging by whole body 18F-FDG PET/MR might help as a new approach.

Methods: 14 whole body 18F-FDG-PET/MR examinations were performed in 12 patients with IRF in a clinical setting. MR imaging by T1w and T2w sequences was used for anatomical localization of FDG uptake and identification of morphological changes associated with IRF. In addition, CE (contrast enhanced)-MRA was performed to judge the lumen of the aorta and the major branches. FDG-uptake was assessed visually (using a 4-point scale) and quantitatively (maximal standardized uptake value [SUV max], target to background ratio [TBR]). Correlations between PET/MR findings (SUV max, TBR and IRF volume calculated on MRI), clinical and laboratory parameters were analyzed. Intended therapeutic management was documented before and after availability of PET/MR findings.

Results: On clinical grounds, 7 cases were classified as having active disease and 7 as inactive. In contrast, PET/MR revealed active IRF in 10/14 scans (71%) and changed disease status in 5 cases (36%), more specifically in 4 cases from inactive to active disease and active to inactive disease in 1 case. PET/MR showed vessel changes suggestive for active LVV in 3 cases.

Conclusion: Whole body 18F-FDG-PET/MR may be considered as a useful approach in the management of patients with IRF.