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.
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