How would you check for a venous clot in the iliac vein?

Diagnostic Approach to Iliac Vein Thrombosis

For suspected iliac vein thrombosis, the recommended initial diagnostic approach is compression ultrasound with Doppler imaging of the iliac veins, followed by CT venography or MR venography if ultrasound is negative but clinical suspicion remains high. 1, 2

Initial Evaluation

• Compression ultrasound with Doppler imaging of the iliac veins is the first-line diagnostic test for suspected iliac vein thrombosis 1

  • Look for non-compressible venous segments
  • Assess for abnormal Doppler waveforms in the common femoral vein (continuous or asymmetrical flow patterns suggest more central obstruction)
  • Whole-leg swelling with normal compression ultrasound should raise suspicion for iliocaval disease 1

• Clinical presentation suggestive of iliac vein thrombosis:

  • Entire leg swelling (not just calf or thigh)
  • Flank, buttock, or back pain
  • Normal proximal compression ultrasound despite significant symptoms 1

When Initial Ultrasound is Negative or Indeterminate

If the initial compression ultrasound is negative but clinical suspicion for iliac vein thrombosis remains high:

1. CT venography (CTV) - preferred for most patients due to:

   • Wider availability
   • Faster acquisition time
   • Equivalent diagnostic accuracy to MRV
   • Can visualize the entire iliocaval system 2, 3

2. MR venography (MRV) - particularly valuable when:

   • Patient is pregnant
   • Renal dysfunction is present
   • Contrast allergy exists
   • Radiation exposure is a concern 1, 2

3. Doppler ultrasound of the iliac vein - may be attempted but has technical limitations 1

Special Considerations

Pregnant Patients

• For pregnant women with suspected DVT including iliac vein involvement:
  • Begin with compression ultrasound with iliac vein imaging
  • If initial ultrasound is negative, perform serial compression ultrasound on days 3 and 7
  • Consider MR venography for suspected isolated iliac vein thrombosis to avoid radiation exposure 1

Iliac Vein Compression Syndrome

• Consider iliac vein compression syndrome (May-Thurner syndrome) as a potential cause, especially with left-sided iliofemoral DVT 4, 5
• CT venography or MR venography can identify compression of the left common iliac vein by the right common iliac artery 3

Common Pitfalls to Avoid

• Failing to consider iliac vein thrombosis when standard proximal compression ultrasound is negative despite significant symptoms 2
• Relying solely on ultrasound without additional imaging when iliac vein thrombosis is suspected, as ultrasound has anatomical limitations above the inguinal canal 2
• Missing the diagnosis due to inadequate imaging of the pelvic veins, which can lead to clot propagation and post-thrombotic syndrome 1, 5

Follow-up Testing

• If initial tests are indeterminate, consider:
  • Serial ultrasound examinations (days 3 and 7)
  • D-dimer testing (helpful if negative)
  • Proceeding directly to advanced imaging if clinical suspicion remains high 1

By following this diagnostic algorithm, clinicians can effectively diagnose iliac vein thrombosis and initiate appropriate treatment to prevent complications such as pulmonary embolism and post-thrombotic syndrome.