Normal Internal Carotid Artery Stenosis Grading on Ultrasound
The internal carotid artery (ICA) supplies the anterior cerebral circulation, and significant stenosis is a major modifiable risk factor for ischemic stroke. Duplex ultrasound—combining gray-scale imaging with Doppler velocity measurements—is the first-line noninvasive tool for detecting and grading ICA stenosis. Accurate stenosis classification directly guides decisions regarding medical management versus surgical or endovascular intervention.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Normal | PSV is <125 cm/sec, no plaque or intimal thickening |
| <50% | PSV is <125 cm/sec, ICA/CCA PSV ratio <2.0, EDV <40 cm/sec |
| 50-69% | PSV is 125-230 cm/sec, ICA/CCA PSV ratio of 2.0-4.0, EDV of 40-100 cm/sec |
| ≥70% | PSV is >230 cm/sec, ICA/CCA PSV ratio >4, EDV >100 cm/sec |
| Near Occlusion | Variable velocity parameters which may be high, low, or undetectable. |
| Total Occlusion | No detectable luminal patency. |
Clinical Significance
Stenosis grading is clinically critical because symptomatic patients with 50–69% stenosis and those with ≥70% stenosis have demonstrated benefit from carotid endarterectomy in landmark trials. The three primary Doppler parameters used together are peak systolic velocity (PSV), end-diastolic velocity (EDV), and the ICA-to-common carotid artery (CCA) PSV ratio. Relying on a single parameter alone increases misclassification risk.
Near-occlusion represents a particularly challenging diagnostic category: the residual lumen may be so severely narrowed that velocities paradoxically fall, potentially mimicking a less severe lesion or even total occlusion. Gray-scale and color Doppler assessment of luminal patency are essential in this context. Total occlusion shows no detectable flow and must be differentiated from near-occlusion, as surgical options differ significantly.
- ≥70% stenosis: High stroke risk; typically warrants revascularization in symptomatic patients
- 50–69% stenosis: Intermediate risk; intervention decisions individualized based on symptoms and comorbidities
- <50% stenosis: Generally managed medically with risk factor modification
- Near occlusion: Variable velocities; requires confirmatory CTA or MRA
- Total occlusion: No intervention benefit; anticoagulation or antiplatelet therapy considered
Reference: Grant E, Benson C, Moneta G et al. Carotid Artery Stenosis: Gray-Scale and Doppler US Diagnosis–Society of Radiologists in Ultrasound Consensus Conference. Radiology. 2003;229(2):340-6. doi:10.1148/radiol.2292030516
Imaging Notes
On duplex ultrasound, the Doppler sample volume should be placed in the proximal ICA at the site of maximum velocity, with the angle of insonation maintained at 60° or less to ensure velocity accuracy. PSV, EDV, and the ICA/CCA PSV ratio should all be recorded and interpreted together per the SRU consensus criteria. The CCA PSV for the ratio is measured in the distal common carotid artery, away from the bifurcation.
Gray-scale imaging should assess plaque morphology, echogenicity, and surface characteristics, while color Doppler helps identify the region of aliasing or flow disturbance to guide sample placement. Contralateral high-grade stenosis or occlusion can elevate ipsilateral velocities due to collateral flow, potentially overestimating stenosis severity—a key interpretive pitfall that should be noted in the report.