<prompt> Most common organ involved in retroperitoneal fibrosis is?AortaUreterInferior vena cavaSympathetic nerve plexus  <response>: Ans. b UreterRef.: Campbell 10th ed. 1108-1112 Ureters are involved most commonly. MC site is lower third. Obstructive uropathy is the earliest and most common specific symptom. 70 cases are primary or idiopathic Ormonds disease Investigation of choice is CT scan. In patients with renal compromise, MRI is the investigation of choice. 