• Inflammatory and fibrous retroperitoneal tissue around infrarenal aorta and iliacs
• Etiologies
• Idiopathic (immune related)
• Malignancy - carcinoid, lymphoma, sarcoma, colorectal, breast, bladder, prostate
• Radiation
• Drugs, infection

• Dull poorly localized flank/back pain
• Hydronephrosis

CT

• Medial ureteral deviation

• First line include steroids (eg 60 mg prednisone daily x 6 weeks) or tamoxifen (a nonsteroidal anti-estrogen).
• Mycophenolate mofetil, azathioprine, or cyclophosphamide can also be used as primary or salvage therapy, but those agents are used in combination with steroids