A cold, painful limb: the CT angiogram shows where the vessel stops, whether it is embolic (sharp meniscus, normal vessels elsewhere) or thrombotic (on a background of atheroma), and the run-off below — the vascular surgeon plans embolectomy or lysis from it.
Orient first
- Embolic occlusion: abrupt cut-off at a bifurcation (common femoral, popliteal trifurcation) with little atheroma and poor collaterals; look for the source in the heart or aorta.
- In-situ thrombosis: occlusion at a stenosis on diffuse atheroma, often with collaterals.
- Bypass graft or stent occlusion is its own category — report graft patency first.
Acquire the study
- CT angiography of the aorta and both legs to the feet (bolus-tracked arterial phase, 1 mm slices) with a delayed acquisition of the calves if distal vessels have not filled; MIP and curved reformats.
The manoeuvre
- Axial source images from the aorta down: first level of occlusion, its shape (meniscus of contrast = embolus) and length in cm.
- Run-off: which tibial vessels reconstitute below the occlusion; state if nothing fills to the ankle.
- Delayed phase through the calves when the arterial phase shows no distal filling — slow flow can mimic occlusion.
- Search for the source: left atrial appendage or ventricular thrombus if the heart is covered, aortic mural thrombus, popliteal aneurysm.
- Soft tissues: muscle oedema or compartment swelling suggests established ischaemia.
What confirms it
- An arterial occlusion with a compatible clinical picture — typed as embolic or thrombotic — with the reconstitution level stated.
What licenses you to exclude it
- Opacified arteries to the pedal vessels on arterial and delayed phases exclude a proximal arterial occlusion.
The classic misread
- Calling an occlusion because the bolus was timed too early for a slow limb — always check the delayed phase.
- Missing a popliteal aneurysm with thrombus as the source.