Lower Limb Venous Duplex
Lower limb venous duplex ultrasound examines the deep veins (common femoral, femoral, deep femoral, popliteal, calf veins: posterior tibial, peroneal, and muscular veins) and superficial veins (great saphenous, small saphenous, and perforators) with B-mode compression and colour and spectral Doppler.
A 5 to 10 MHz linear probe is used (a lower frequency curvilinear probe for the proximal veins in obese patients). For deep vein thrombosis (DVT), the key sign is non-compressibility of the vein under gentle probe pressure; colour Doppler shows absent or partial flow, and the augmentation manoeuvre (distal calf squeeze) increases flow in patent veins.
For venous insufficiency, the patient stands and reflux is shown after distal compression or with the Valsalva manoeuvre (reflux lasting over 0.5 seconds in superficial veins and over 1 second in femoral and popliteal veins). The examination takes 15 to 30 minutes, with no radiation.
Venous thromboembolism affects 1 to 2 in each 1000 people each year, with DVT in the legs responsible for most pulmonary emboli. Untreated proximal DVT leads to pulmonary embolism in up to 50% of cases, and post-thrombotic syndrome develops in 20 to 50% of patients.
Compression ultrasound has a sensitivity of 95% and specificity of 96% for symptomatic proximal DVT, and lower sensitivity (about 60 to 75%) for isolated calf DVT and asymptomatic DVT. Chronic venous disease affects 20 to 30% of adults, with varicose veins being the most frequent, and duplex is the basis of mapping before surgery or endovenous ablation.
Indications. Suspected DVT (leg swelling, pain, tenderness, erythema, after assessment of pre-test probability and D-dimer). Suspected pulmonary embolism with no chest imaging possible. Source of embolus. Follow up of known DVT (extension, recanalisation).
Varicose veins and chronic venous insufficiency (mapping of reflux, perforators, saphenofemoral and saphenopopliteal junctions). Planning of endovenous ablation, foam sclerotherapy or surgery. Superficial vein thrombosis (extension towards the deep system within 3 cm of the junction). Leg swelling of unknown cause, Baker cyst complications, haematoma, lymph nodes.
Assessment before and after vein harvest for bypass, or of veins for arteriovenous fistula. Vena cava filter assessment. Not for routine screening of asymptomatic patients.
Contraindications and precautions. None. For DVT, gentle pressure is applied to avoid dislodging thrombus (the risk is theoretical and very low). The patient lies supine with the leg externally rotated and knee slightly flexed; reverse Trendelenburg tilt helps vein filling. For reflux, the patient stands with weight on the opposite leg. Dressings, casts, pain and obesity limit examination.
Preparation and technique. No fasting is needed. Compression ultrasound examines the common femoral vein at the groin and each vein down to the popliteal trifurcation at about 1 to 2 cm intervals.
A two point technique at the common femoral and popliteal veins misses isolated femoral vein thrombi, so a complete proximal technique is preferred.
Whole leg technique includes the calf veins. The vein is compressible if the walls come together completely. The contralateral leg is compared.
Reflux testing is done in standing position at the saphenofemoral junction, the great saphenous vein at thigh and calf levels, the saphenopopliteal junction, the small saphenous vein, and incompetent perforators (diameter over 3.5 mm, outward flow over 0.5 seconds).
