What investigations should be done in patients with suspected renal vein thrombosis for an accurate diagnosis?

Diagnostic Investigations for Renal Vein Thrombosis

For suspected renal vein thrombosis, CT angiography (contrast-enhanced CT) is the investigation of choice, with MR angiography or Doppler ultrasound as acceptable alternatives when CT is contraindicated. 1

Initial Imaging Modality

CT angiography with contrast enhancement should be the first-line imaging study for patients with suspected renal vein thrombosis, as it provides the most comprehensive evaluation of both the renal veins and inferior vena cava while also assessing for complications such as pulmonary embolism. 2, 1

Alternative Imaging Options

When CT angiography is not available or contraindicated (e.g., renal insufficiency, contrast allergy):

• Duplex Doppler ultrasound can demonstrate absent intrarenal and renal venous flow in early stages and directly visualize thrombus in the renal vein and IVC 3, 2
• MR angiography offers excellent noninvasive assessment of renal vein patency and thrombus depiction, particularly useful in patients requiring contrast avoidance 1, 4
• Renal venography should be reserved only for highly selected patients when noninvasive studies are inconclusive 1

Ultrasound Findings to Recognize

In the acute phase, Doppler ultrasound demonstrates: 3

• Absent intrarenal venous flow on color Doppler
• Highly echogenic streaks representing interlobular and interlobar thrombus (persist only a few days)
• Kidney swelling with increased echogenicity and prominent echopoor medullary pyramids in the first week
• Direct visualization of thrombus within the renal vein and IVC on gray-scale imaging

CT Angiography Advantages

CT with contrast injection provides superior diagnostic information by: 2

• Directly visualizing thrombus within the renal vein
• Assessing for extension into the inferior vena cava
• Identifying underlying causes (obstructive stones, collections)
• Detecting complications such as pulmonary embolism
• Evaluating for alternative diagnoses

MRI Considerations

MR flow imaging offers good correlation with other modalities (agreement in 16 of 19 cases compared to ultrasound in one series) and provides: 4

• Noninvasive vascular patency assessment
• Direct thrombus depiction
• Avoidance of ionizing radiation and iodinated contrast

Common Diagnostic Pitfalls

Do not rely on intravenous pyelography (IVP) as it may be normal in chronic renal vein thrombosis despite the presence of thrombus, and abnormalities are only characteristic in acute presentations. 5

Recognize that ultrasound findings evolve rapidly - the highly echogenic streaks of early thrombosis persist only for a few days, so timing of imaging is critical. 3

Consider pulmonary embolism screening with CT pulmonary angiography or ventilation-perfusion scanning, as thromboembolic complications are common, particularly in patients with chronic renal vein thrombosis and nephrotic syndrome. 2, 5

Clinical Context for Imaging Selection

The choice between imaging modalities should account for:

• Neonates: Ultrasound with color Doppler is preferred as the initial accessible and reliable tool 3
• Adults with nephrotic syndrome: CT angiography to evaluate both acute and chronic thrombosis 1, 5
• Suspected acute pyelonephritis complication: CT with contrast to identify both infection source and venous thrombosis 2
• Pregnancy or renal insufficiency: MR angiography as the preferred alternative 1, 4