ICA Stenosis Grading (SRU Consensus)
| NASCET % Stenosis | PSV (ICA) | ICA/CCA PSV Ratio | EDV (ICA) |
|---|---|---|---|
| <50% | <125 cm/s | <2.0 | <40 cm/s |
| 50–69% | 125–230 cm/s | 2.0–4.0 | 40–100 cm/s |
| ≥70% | >230 cm/s | >4.0 | >100 cm/s |
| Near occlusion | Variable (may be low) | Variable | Variable |
| Total occlusion | No flow | — | — |
Near occlusion pitfall: With near-total ICA occlusion, velocities may paradoxically be LOW due to markedly reduced flow volume — do not mistake for mild stenosis. Color Doppler showing a thread-like "string sign" and absent or severely dampened waveform confirms near-occlusion. Clinical and CT-angiographic correlation is essential.
ICA/CCA ratio is the most robust single parameter when PSV is affected by contralateral disease, cardiac arrhythmia, or elevated CO. Use all three parameters together — no single value alone determines stenosis grade.
Key Pearls
- >70% stenosis — symptomatic patients benefit from carotid endarterectomy (CEA); asymptomatic threshold is ≥80% at most centers
- Bilateral disease — elevated CCA velocity on one side artificially lowers the ICA/CCA ratio; use PSV + EDV together
- Post-stent surveillance — velocity thresholds differ from native vessel; PSV >300 cm/s or ratio >4.75 suggests in-stent restenosis ≥50%
Reference
Grant EG et al. Carotid artery stenosis: gray-scale and Doppler US diagnosis — Society of Radiologists in Ultrasound Consensus Conference. Radiology. 2003;229(2):340–6.