Acute renal vein thrombosis and nephrotic syndrome in the setting of retroperitoneal fibrosis.

Idiopathic retroperitoneal fibrosis (RPF) is a rare disease that involves non-specific inflammation and fibrosis surrounding the aorta. As a result, RPF is a challenging diagnosis to make; patients often seek medical attention after complications arise, such as nephrotic syndrome. The patient in our case report initially complained of flank pain. Laboratory evaluation revealed acute renal failure and nephrotic syndrome with substantial proteinuria. Multiple imaging modalities demonstrated a large, ill-defined, infiltrative retroperitoneal soft tissue mass that encased the great vessels. The patient was also noted to have acute left renal vein thrombosis. Although the patient was eventually diagnosed with RPF of unknown etiology, his clinical course is particularly unique given the rarity of the renal vein thrombosis. This case report adds a value to the medical community by helping to elucidate RPF and exposing its potentially life-threatening complications.