ICA Stenosis Grading (IAC 2023 Criteria)
| Degree of Stenosis | ICA PSV | Plaque Estimate | ICA/CCA PSV Ratio | ICA EDV |
|---|---|---|---|---|
| Normal | <180 cm/s | None | <2.0 | <40 cm/s |
| <50% | <180 cm/s | <50% diameter reduction | <2.0 | <40 cm/s |
| 50–69% | 180–230 cm/s | ≥50% diameter reduction | 2.0–4.0 | 40–100 cm/s |
| >70% but < near occlusion | >230 cm/s | ≥50% diameter reduction | >4.0 | >100 cm/s |
| Near occlusion | High, low, or undetectable | Visible (severe) | Variable | Variable |
| Total occlusion | Undetectable | Visible, no detectable lumen | N/A | N/A |
Footnote: ICA PSV 125–180 cm/s with ICA/CCA PSV ratio ≥2.0 is also consistent with 50–69% stenosis, particularly when plaque is present. Use all parameters in combination — no single value alone determines stenosis grade.
Near occlusion pitfall: With near-total ICA occlusion, velocities may paradoxically be LOW due to markedly reduced flow volume — do not mistake for mild disease. Color Doppler showing a thread-like "string sign" and severely dampened or absent waveform confirms near-occlusion. CT angiography correlation is essential.
Key Pearls
- Normal vs. <50% — IAC 2023 distinguishes a true Normal category (no plaque, PSV <180) from mild disease with plaque present but <50% diameter reduction
- >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%
- IAC 2023 vs. SRU 2003 — key change: the PSV threshold for 50% stenosis raised from 125 → 180 cm/s; plaque assessment now formally incorporated
Reference
Intersocietal Accreditation Commission (IAC). Updated Carotid Ultrasound Criteria. November 2023. intersocietal.org