What does a monophasic lower extremity Doppler (Doppler ultrasound of the legs) mean?

Monophasic Lower Extremity Doppler: Clinical Significance

A monophasic Doppler waveform in the lower extremity indicates abnormal blood flow and suggests proximal obstruction—either arterial disease when found in arteries or venous obstruction when found in veins—and requires further investigation to identify the underlying cause. 1

Understanding Doppler Waveform Patterns

Normal vs. Abnormal Waveforms

• Normal arterial waveforms are triphasic or biphasic, showing forward flow, brief reverse flow, and forward flow again, reflecting healthy vessel elasticity and low resistance 1
• Monophasic waveforms indicate dampened flow with loss of the normal pulsatile pattern, suggesting significant proximal disease 2, 3
• The transition from triphasic → biphasic → monophasic represents progressive arterial disease severity 3

Clinical Significance in Arterial Disease

Diagnostic Implications

• Monophasic arterial waveforms indicate hemodynamically significant stenosis (typically >50% diameter reduction) upstream from the measurement site 1, 3
• In patients with diabetic foot ulcers on dialysis, poor monophasic waveforms in the dorsalis pedis or posterior tibial arteries independently predict major lower extremity amputation (odds ratio 7.61, sensitivity 88%, specificity 59.6%) 2
• Monophasic waveforms correlate with more severe peripheral artery disease and reduced perfusion to the limb 2, 3

Anatomic Localization

• Segmental Doppler studies with waveform analysis help localize disease to aortoiliac, femoropopliteal, or infrapopliteal segments 1
• The location where waveforms transition from normal to monophasic indicates the approximate level of significant stenosis 3

Clinical Significance in Venous Disease

Venous Obstruction Indicators

• Monophasic waveforms in the common femoral vein are reliable indicators of proximal venous obstruction, with high specificity for iliac vein or IVC pathology 1, 4
• Loss of respiratory phasicity and cardiac pulsatility in venous waveforms indicates obstruction between the measurement site and the heart 1, 5
• In a retrospective study of 2,963 venous Doppler examinations, monophasic common femoral vein waveforms identified proximal obstruction in 124 cases, with 47 showing iliac vein thrombosis and 26 showing extrinsic compression 4

Causes of Venous Monophasic Waveforms

• Deep venous thrombosis extending into iliac veins (most common pathologic cause) 1, 4
• Extrinsic compression from masses, aneurysms, or other structures 5, 4
• Severe iliac vein occlusive disease from chronic venous disease or May-Thurner syndrome 1
• Hypoplastic or stenosed iliac veins 4

Recommended Diagnostic Algorithm

When Monophasic Arterial Waveforms Are Found:

1. Document the anatomic level where waveforms become monophasic to localize disease 1
2. Measure ankle-brachial index (ABI) if not already done—monophasic waveforms typically correlate with ABI ≤0.90 1
3. Consider anatomic imaging (CTA, MRA, or angiography) if revascularization is being considered for symptomatic patients 1
4. In diabetic patients on dialysis with foot ulcers, monophasic waveforms warrant aggressive wound care and early vascular surgery consultation given high amputation risk 2

When Monophasic Venous Waveforms Are Found:

1. Evaluate the external iliac veins sonographically for thrombosis, as iliac vein DVT is clinically important but may be missed on standard compression ultrasound 4
2. Obtain cross-sectional imaging (CT or MRI) to determine the cause of obstruction, particularly to identify extrinsic compression or central venous thrombosis 1, 4
3. Assess for bilateral findings—unilateral monophasic waveforms suggest ipsilateral iliac obstruction, while bilateral findings suggest IVC obstruction 1

Critical Pitfalls to Avoid

• Do not assume compressible veins exclude significant pathology—veins may be compressible at the examination site but have critical obstruction proximally 5, 4
• Standard DVT protocols examining only thigh to knee may miss iliac vein thrombosis that causes monophasic femoral vein waveforms 4
• In patients with non-compressible arteries (ABI >1.40), arterial waveform analysis becomes even more important for assessing perfusion, as pressure measurements are unreliable 1
• Monophasic waveforms have low sensitivity but high specificity for proximal obstruction—normal waveforms do not exclude disease, but abnormal waveforms strongly suggest it 1, 4

Quality of Life and Prognostic Implications

• Monophasic arterial waveforms in patients with critical limb-threatening ischemia indicate severe perfusion compromise requiring urgent revascularization consideration 1, 2
• Untreated venous obstruction causing monophasic waveforms can lead to post-thrombotic syndrome, chronic venous insufficiency, and venous ulceration 1
• Early identification and treatment of the underlying obstruction improves limb salvage rates and prevents long-term disability 1, 2