Retroperitoneal fibrosis is a rare disorder in which fibrous tissue proliferates in the retroperitoneal space, gradually encasing the abdominal aorta, ureters, and adjacent structures. Onset is insidious and early complaints are non-specific, so diagnosis is often delayed. Dull, persistent painDeep, aching discomfort is the most frequent first symptom. Pain is usually felt in the flank, lower back, or iliac fossa, may radiate to the groin or anterior thigh, and is characteristically unrelieved by rest or change of posture; NSAIDs give only temporary relief. Constitutional symptomsLow-grade fever, fatigue, anorexia, weight loss, and general malaise accompany the inflammatory phase in more than... Learn more