Retroperitoneal fibrosis is a disorder in which the tubes that carry urine from the kidneys to the bladder are blocked by a fibrous mass in the back of the abdomen.

Retroperitoneal fibrosis is a rare disorder caused by an excess of fibrous tissue in the area just behind the stomach. Doctors don't know why these masses form. It is most common in people aged 40 - 60, and men are twice as likely to develop them as women.

The disorder may cause chronic unilateral obstructive uropathy or chronic bilateral obstructive uropathy, which result when the fibrous mass blocks the ureters.The symptoms are caused by the obstruction of the ureters, the tubes that carry urine from the kidneys to the bladder.

Early symptoms:

• Dull pain in the abdomen that increases with time
• Swelling of one leg
• Decreased circulation in the legs leading to pain and discoloration
• Severe abdominal pain with hemorrhage due to ischemic bowel

Later symptoms:

• Decreased urine output
• Total lack of urine (anuria)
• Nausea, vomiting, changes in thinking caused by kidney failure and the resulting build-up of toxic chemicals in the blood.

• Serum BUN and creatinine showing elevated levels
• Kidney ultrasound showing hydronephrosis (distention of the kidney pelvis because of fluid accumulation) and a mass
• Excretory urography showing compression and deviation of the ureters
• Abdominal CT scan (the best test to reveal the retroperitoneal mass)
• MRI (compares well to the CT scan)
• Biopsy showing either retroperitoneal fibrosis or a cancerous tumor