The diagnosis of retroperitoneal fibrosis cannot be made on the basis of the results of laboratory studies. CT is the best diagnostic modality: a confluent mass surrounding the aorta and common iliac arteries can be seen. On MRI, it has low T1 signal intensity and variable T2 signal. Malignant retroperitoneal fibrosis usually give uneven MRI signals, bulky, extend above the origins of renal arteries, or displace aorta anteriorly. Besides, malignant retroperitoneal fibrosis less frequently displaces ureter medially when compared to other retroperitoneal fibrosis.