Module · DVT
FUSIC DVT resources
10 scans, 5 directly observed. At least 1 must demonstrate a DVT. Two main sites: inguinal crease (femoral) and popliteal fossa. Systematic 1 cm compression throughout.
Anatomy: the veins you must knowCFV, saphenous junction, deep femoral, popliteal, trifurcation — map them before you scan.
Use a linear probe (7–12 MHz). Femoral vessels are 2–4 cm deep; popliteal 2–3 cm.
Inguinal region (proximal to distal):
- Common femoral vein (CFV): Lies medial to the common femoral artery. Thin-walled, compressible, slight respiratory variation, no pulsation.
- Saphenofemoral junction (SFJ): 2–4 cm distal to inguinal ligament. Great saphenous vein joins CFV medially. Isolated saphenous thrombosis = not proximal DVT but document.
- CFV/DFV confluence: ~4–6 cm distal to SFJ. CFV splits into superficial femoral vein (SFV — confusingly a deep vein) and deep femoral vein (DFV). Both are examination points.
Popliteal fossa:
- Patient prone or lateral decubitus, knee slightly flexed.
- Popliteal artery: Deeper (further from probe), pulsatile.
- Popliteal vein (PV): Superficial to artery, compressible, no pulsation.
- Trifurcation: Divides into anterior tibial, posterior tibial, and peroneal veins just distal to the joint line. Identify the trifurcation but calf veins are beyond FUSIC DVT scope.
Compression techniqueThe 1 cm systematic compression method — reproducible and interpretable.
Apply firm, steady downward pressure with the probe in short axis (transverse). A normal vein completely collapses — walls touch. A thrombosed vein does not compress.
Two-point CUS (minimum): Compress at the CFV/SFJ level AND at the popliteal vein. Covers the two most common proximal DVT sites.
Full compression: Advance the probe in 1 cm increments from inguinal ligament to popliteal trifurcation. Compress at every step.
Technique tips:
- Start in transverse. Apply enough pressure to slightly deform the adjacent artery — this confirms adequate compression force.
- Partial collapse is NOT normal. Full collapse is required.
- If the vein doesn’t collapse, try repositioning the limb or using the other hand to support the limb from underneath.
Normal vs thrombosed appearancesB-mode findings — and why compression, not echogenicity, is the key.
Normal vein: Anechoic lumen, thin smooth walls, complete collapse, slight respiratory diameter variation.
Acute DVT: Non-compressible — the key finding. Lumen may appear hypoechoic (early) or isoechoic (nearly invisible). Vein often distended compared to the adjacent artery.
Chronic DVT: More echogenic/heterogeneous thrombus. Thickened, irregular walls. Vein may be small and scarred (recanalized) but still non-compressible.
Colour Doppler & augmentationConfirming flow, phasicity, and downstream patency.
Colour Doppler supplements compression — it does not replace it.
Normal venous Doppler:
- Spontaneous low-velocity non-pulsatile flow with respiratory variation (phasicity)
- Augmentation on calf compression: sudden surge in flow in popliteal/femoral veins, confirming no distal obstruction
Abnormal:
- Absent spontaneous flow — proximal obstruction or very low cardiac output
- Continuous (non-phasic) flow — suggests proximal obstruction (iliac vein DVT or external compression)
- Absent augmentation — obstruction between calf and interrogated point
Clinical integration & documentationWhat to do with a positive scan and the limits of FUSIC DVT.
FUSIC DVT is a rule-in, not rule-out examination. A positive scan (non-compressible vein) is highly specific and should be acted on. A negative scan in high clinical suspicion does not exclude calf vein DVT or iliac thrombosis — refer for formal duplex.
FUSIC DVT scope: Common femoral, superficial femoral (femoral), and popliteal veins (proximal DVT). Calf veins are NOT within scope.
After a positive scan:
- Inform the clinical team immediately for anticoagulation decision (NICE NG158)
- Document the examination point and store images per departmental policy
- Do not document in the medical record during training — wait for accredited practitioner review
Pitfalls & mimicsThings that look like DVT — and things that make DVT harder to find.
- Inguinal lymph nodes: Common, oval, hypoechoic with echogenic hilum. Compressible. Confirm you are in the correct vessel.
- Baker’s cyst (popliteal): Anechoic structure, not a vessel — no flow on Doppler, attached to joint, does not compress the adjacent vein.
- Muscle haematoma: Echogenic/heterogeneous mass within muscle, no flow, not pulsatile.
- Duplicated femoral vein: SFV is duplicated in ~25% of patients. Two parallel veins alongside the SFA — compress both. Missing the duplicate causes false negatives.
- Extrinsic compression: Haematoma, tumour, or lymph node can obstruct the vein without intraluminal thrombus. Vein non-compressible but no visible thrombus — refer for formal duplex.