Renal Vein Thrombosis

Renal vein thrombosis (RVT) is the formation of a blood clot within the renal vein, which can be unilateral or bilateral. In adults, the most common cause is nephrotic syndrome — specifically membranous nephropathy (highest RVT risk among nephrotic syndromes). Nephrotic syndrome creates a hypercoagulable state through urinary loss of antithrombin III (a major natural anticoagulant), increased hepatic synthesis of clotting factors (fibrinogen, factor V, VIII), decreased fibrinolysis, and hyperviscosity from elevated lipids. Other causes include renal cell carcinoma (tumor thrombus extending into the renal vein and IVC), trauma, dehydration (especially in neonates), and hypercoagulable states (antiphospholipid syndrome, factor V Leiden). Acute RVT presents with sudden flank pain, hematuria, and acute kidney injury. Chronic RVT may be asymptomatic with gradual collateral vein development. Left-sided RVT is more common because the left renal vein is longer and passes between the aorta and superior mesenteric artery (nutcracker anatomy). Complications include pulmonary embolism (clot extends into IVC), renal infarction, and progressive renal impairment.