Retroperitoneal Fibrosis (RPF)
Retroperitoneal fibrosis is a sheet of inflammatory scar tissue that grows around the distal aorta and engulfs the ureters, squeezing them until the kidneys obstruct — often both at once.
The big picture
Retroperitoneal fibrosis is a sheet of inflammatory scar tissue that grows around the distal aorta and engulfs the ureters, squeezing them until the kidneys obstruct — often both at once. The signatures that make it recognisable are a periaortic mass at L4–L5, ureters pulled medially (the opposite of most masses, which push them out), and a dramatic response to steroids. The two jobs are to relieve the obstruction and to rule out an underlying malignancy masquerading as benign fibrosis.
The framework: a periaortic fibro-inflammatory mass (mostly idiopathic/IgG4-related) → medial entrapment of the ureters → bilateral obstruction → steroids ± ureterolysis, after excluding malignancy.
Mechanism pathway
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Diagnostic algorithm
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Board traps
RPF centres on the distal aorta (L4–L5) and wraps the ureters → usually BILATERAL obstruction.
Medial deviation of the ureters is the classic sign (most masses deviate ureters laterally).
~70% idiopathic (chronic periaortitis / IgG4-spectrum); secondary causes include drugs (ergots), malignancy, radiation, aneurysm.
Always exclude underlying malignancy — malignant RPF mimics idiopathic; biopsy when in doubt.
Steroids are the medical mainstay (~80% response); tamoxifen/immunosuppressants adjuncts.
Decompress (stent/nephrostomy) first; ureterolysis for refractory/persistent obstruction.