Ultrasound Imaging of Renal Vein Thrombosis

Renal Vein Thrombosis

• Most commonly associated with membranous nephropathy, producing the nephrotic syndrome
• Also associated with systemic lupus erythematosus, diabetes, glomerulonephritis, hypovolaemic shock, and renal transplantation
• Abnormalities of coagulation, involving clotting factors, the fibrinolytic system, and platelets, can be demonstrated
• Dehydration more commonly associated with renal vein thrombosis in infants, but may occur in adults, particularly in hot climates
• Renal cell carcinoma may invade the renal vein and produce a tumour thrombus, which can extend into the inferior vena cava (IVC) and provide a source of emboli

Ultrasound Imaging of Renal Vein Thrombosis

• Sudden complete occlusion of the main renal vein produces an enlarged, echo-poor kidney
• Changes develop over the initial 24 hours, due to swelling of the parenchyma
• Echo-free areas of haemorrhagic infarcts can be distinguished within the generally echo-poor tissue
• Renal sinus echoes may be markedly compressed by the swollen parenchyma
• After 10–14 days, the kidney starts to shrink, resulting in a small kidney with abnormally high reflectivity
• Corticomedullary differentiation is initially preserved, but is lost after 3–4 weeks as the kidney contracts

Renal Artery Occlusion

• Sudden renal infarction can occur from various causes, including atheromatous plaque haemorrhage, aortic dissection, emboli, and traumatic avulsion
• Unilateral renal artery occlusion does not produce renal failure, and without Doppler, may be difficult to detect with ultrasound
• In the immediate acute stage, the affected kidney may be normal in size and have normal reflectivity, but a small increase in size compared with the perfused contralateral kidney may be demonstrated
• In some patients, a subcapsular ‘halo’ or rim of echo-poor tissue can be seen, which is thought to correspond to oedematous perfused tissue fed by capsular collateral vessels
• In the longer term, the affected kidney slowly shrinks with smooth margins and no dilatation of the collecting system

Medullary Changes and Corticomedullary Differentiation

• Medullary pyramids may be more prominent in many cases of parenchymal disease, due to increased cortical reflectivity
• In acute conditions involving primarily the medulla, such as acute tubular necrosis, the pyramids can be enlarged due to oedema
• Increased medullary reflectivity can be detected in nephrocalcinosis of any etiology and also in some other conditions such as gout

Vascular Disorders

• Renal vein thrombosis may be seen in up to 40% of septic or dehydrated infants
• Acute presentation with renal vein thrombosis is rare in adults, but when it does occur, it is generally unilateral or restricted to one segment and clinical renal failure does not occur