<prompt> Most common organ involved in retroperitoneal fibrosis is -AortaUreterInferior vena cavaSympathetic nerve plexus  <response>: The most important clinical aspect of retroperitoneal fibrosis is that the fibrotic process frequently entraps and constricts the ureters thereby causing obstructive uropathy.Retroperitoneal fibrosis -It is a nonspecific, nonsuppurative inflammation of fibro-adipose tissue of unknown cause that produces symptoms by the gradual compression of tubular structures in retroperitoneal space.Aetiology of retroperitoneal fibrosis - About 23rd cases are primary idiopathic, are also known as Ormonds diseaseSecondary Retroperitoneal fibrosisa variety of inflammatory conditions - chronic pancreatitis, histoplasmosis, tuberculosis, or actinomycosis.drugsmethysergide most imp.β blockershydralazineα methyldopaEtacapone used in the tt of Parkinsons ds. -malignancies prostate, non-Hodgkins lymphoma, sarcoma, characinoid gastric cancer.antoimmune disorders ankylosing spondylitis, SLE PAN etc.Symptoms of retroperitoneal fibrosis -It is more common in men between 40-60 yrs of ageEarly symptoms are nonspecific and vague. These arePain Dull noncolicky and insidious in onset.Anorexia, nauseaGeneral malaise, diarrheaLater on, symptoms result from compression of tubular retroperitoneal structures. The major structure involved are-Ureter - Most commonly involvedAortaInferior venacavaSymptoms due to the involvement of ureter usually b1 involvementDysuriaFrequency of urinationChills and fever occur with secondary infection of a hydronephrotic kidney.Hematuria can occur.Diagnosis The diagnosis of retroperitoneal fibrosis usually can be made accurately by intravenous pyelography if uremia is not present.The characteristic finding on pyelogram areHydronephrosis with a dilated tortuous upper ureter.Medial deviation of the ureterExtrinsic ureteral compressionNote: In a retroperitoneal tumor, ureter is laterally deviated while in retroperitoneal fibrosis ureter medially deviates.Currently, the imaging procedure of choice is the CT scan.But if renal function is compromised contrast agents are not given and then MRI is the procedure of choice.TT of Retroperitoneal fibrosis Corticosteroids, with or without surgery, are the mainstay of medical therapy.Surgical treatment is required in patients who present with moderate or massive hydronephrosis. It consists primarily of ureterolysis freeing the ureter from adhesions and surrounding tissue or ureteral stenting..Also, knowPartial or complete ureteral obstruction occurs in 75 to 85 of patients.Most common site of urethral obstruction is lower third of the ureter. 