What does an ultrasound Doppler of the lower leg check for?

Ultrasound Doppler of Lower Leg: Primary Purpose and Clinical Applications

Ultrasound Doppler of the lower leg primarily checks for deep venous thrombosis (DVT), evaluating blood flow through the deep veins from the inguinal ligament to the ankle, including assessment of vein compressibility and flow patterns. 1

Primary Clinical Purpose

• Complete duplex ultrasound (CDUS) is the standard imaging test for diagnosing acute DVT, involving compression of deep veins from the inguinal ligament to the ankle (including posterior tibial and peroneal veins), with spectral Doppler waveforms of common femoral veins and color Doppler imaging 1
• The examination evaluates vein compressibility, with normal veins completely collapsing under probe pressure, while veins containing thrombus remain non-compressible 1
• Doppler ultrasound demonstrates high reliability in DVT diagnosis, with sensitivity of 94% above the knee and 91% below the knee 2

Comprehensive Assessment Components

• Complete duplex ultrasound (CDUS) includes:
  • Compression of deep veins from inguinal ligament to ankle
  • Right and left common femoral vein spectral Doppler waveforms (to evaluate symmetry)
  • Popliteal spectral Doppler assessment
  • Color Doppler imaging 1
• Compression is performed at 2-cm intervals throughout the examination 1
• Symptomatic areas should be evaluated for superficial venous thrombosis or other pathology, especially if deep veins appear normal 1

Clinical Decision Algorithm

1. Patient Risk Assessment:

   • Evaluate pretest probability of DVT using Wells score before ordering ultrasound 1
   • For patients with low (unlikely) pretest probability, high-sensitivity D-dimer testing is appropriate first 1
   • Ultrasound is indicated for patients with likely pretest probability, unlikely probability with positive D-dimer, or when pretest probability was not assessed 1

2. Examination Protocol:

   • Complete duplex ultrasound (CDUS) is preferred over limited protocols 1
   • If CDUS is unavailable, extended compression ultrasound (ECUS) from thigh to knee can be performed as point-of-care testing 1
   • Limited protocols require follow-up testing in 5-7 days to safely exclude DVT 1

3. Follow-up Recommendations:

   • After negative CDUS: repeat scan in 5-7 days if symptoms persist or worsen 1
   • After positive CDUS showing calf DVT without treatment: repeat scan in 1 week or sooner if symptoms progress 1
   • For patients with treated acute DVT: follow-up at the end of treatment to establish new baseline 1

Special Considerations

• Iliocaval DVT may be undetected because thrombus is above the standard examination area; whole-leg swelling with normal compression ultrasound or asymmetrical common femoral Doppler spectra suggests central obstruction 1
• Recurrent DVT can be difficult to diagnose in the absence of an unequivocally new site of acute DVT, as persistent scarring may complicate interpretation 1
• Equivocal findings may require serial imaging after 1-3 and 7-10 days to determine if there are acute changes indicating recurrent DVT 1

Common Pitfalls and Caveats

• Limited protocols examining only thigh to knee require a second study in 5-7 days to safely exclude DVT, as they miss potential calf vein thrombosis 1
• Isolated femoral vein thrombosis (present in 5-7% of DVT cases) may be missed by limited 2-region compression ultrasound 1
• Technical limitations, equivocal findings, or lower sensitivity of calf examination compared to femoropopliteal veins may occasionally result in DVT despite normal CDUS examination 1
• Distinguishing between chronic postthrombotic changes and acute recurrent thrombosis can be challenging and may require serial imaging 1