A perivascular sac with swirling bidirectional (yin-yang) colour flow connected by a neck with to-and-fro spectral flow to the femoral artery — measure sac and neck to choose compression, thrombin or surgery.
Orient first
- Complication of femoral puncture, especially low punctures into the superficial or profunda femoral artery.
- A haematoma has no flow; an arteriovenous fistula has high-velocity continuous flow into a vein.
- Thrombin injection needs a neck long and narrow enough to avoid embolisation.
Acquire the study
- Linear (or curvilinear in large patients) probe over the groin; grey-scale, colour Doppler and spectral Doppler in the neck and the adjacent artery and vein.
The manoeuvre
- Grey-scale: sac size in cm, partial thrombus.
- Colour Doppler: swirling bidirectional flow within the sac (yin-yang sign).
- Neck: length and width in mm; spectral to-and-fro waveform in the neck.
- Which artery it arises from (common femoral, superficial femoral, profunda).
- Common femoral vein: arterialised flow (AV fistula) and compression (DVT).
What confirms it
- A sac with internal swirling colour flow communicating with the artery through a neck with to-and-fro spectral flow.
What licenses you to exclude it
- A collection without internal colour flow and no neck is a haematoma.
The classic misread
- Too high a colour scale hiding slow sac flow.
- Missing an associated AV fistula by not sampling the vein.