Carotid artery stenosis

Duplex ultrasound velocity criteria for the diagnosis and grading of stenosis severity

The test allows stratification of the degree of carotid artery stenosis on the basis of greyscale and Doppler velocity results into the following strata: normal (no stenosis), <50% stenosis, 50% to 69% stenosis, 70% to 79% stenosis, 80% to 99% stenosis, near-occlusion (string sign), and total occlusion.​[24]AbuRahma AF, Srivastava M, Stone PA, et al. Critical appraisal of the Carotid Duplex Consensus criteria in the diagnosis of carotid artery stenosis. J Vasc Surg. 2011 Jan;53(1):53-9;discussion 59-60. http://www.jvascsurg.org/article/S0741-5214(10)01822-7/fulltext http://www.ncbi.nlm.nih.gov/pubmed/20951536?tool=bestpractice.com [30]Nederkoorn PJ, van der Graaf Y, Hunink MG. Duplex ultrasound and magnetic resonance angiography compared with digital subtraction angiography in carotid artery stenosis: a systematic review. Stroke. 2003 May;34(5):1324-32. http://stroke.ahajournals.org/content/34/5/1324.long http://www.ncbi.nlm.nih.gov/pubmed/12690221?tool=bestpractice.com

While velocity criteria have been published for additional categories of stenosis, the key purpose of defining patients with ≥50% stenosis is to identify symptomatic patients who may benefit from revascularisation.

North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria[27]North American Symptomatic Carotid Endarterectomy Trial Collaborators. Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade carotid stenosis. N Engl J Med. 1991 Aug 15;325(7):445-53. http://www.nejm.org/doi/full/10.1056/NEJM199108153250701 http://www.ncbi.nlm.nih.gov/pubmed/1852179?tool=bestpractice.com

The diameter of the arterial lumen at the tightest region of stenosis is compared with the region of the distal internal carotid artery that is free of disease and has non-tapering walls. These criteria have become accepted worldwide and other criteria are rarely used. The formula used to calculate the degree of stenosis is:

Percentage stenosis = [1 - (minimum diameter/distal diameter)] × 100.

European Carotid Surgery Trial (ECST) criteria[31]European Carotid Surgery Trialists' Collaborative Group. MRC European Carotid Surgery Trial: interim results for symptomatic patients with severe (70-99%) or with mild (0-29%) carotid stenosis. Lancet. 1991 May 25;337(8752):1235-43. http://www.ncbi.nlm.nih.gov/pubmed/1674060?tool=bestpractice.com

The diameter of the arterial lumen at the tightest region of stenosis is compared with the estimated normal lumen diameter at the site of the lesion, based on a visual impression of where the normal arterial wall was before development of the stenosis. The formula used to calculate the degree of stenosis is:

Percentage stenosis = [1 - (minimum diameter/estimated normal diameter)] × 100.

Relationship between NASCET and ECST criteria[32]Rothwell PM, Gibson RJ, Slattery J, et al. Equivalence of measurements of carotid stenosis. A comparison of three methods on 1001 angiograms. European Carotid Surgery Trialists' Collaborative Group. Stroke. 1994 Dec;25(12):2435-9. https://www.ahajournals.org/doi/10.1161/01.str.25.12.2435?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%20%200pubmed http://www.ncbi.nlm.nih.gov/pubmed/7974586?tool=bestpractice.com

It is critical that physicians treating carotid disease must specify which methodology was used to arrive at the estimation of stenosis. The degree of stenosis is now usually calculated according to the NASCET criteria, although the ECST criteria may also be used.

The NASCET and ECST estimates of stenosis have a high degree of correlation, but are not numerically similar.[32]Rothwell PM, Gibson RJ, Slattery J, et al. Equivalence of measurements of carotid stenosis. A comparison of three methods on 1001 angiograms. European Carotid Surgery Trialists' Collaborative Group. Stroke. 1994 Dec;25(12):2435-9. https://www.ahajournals.org/doi/10.1161/01.str.25.12.2435?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%20%200pubmed http://www.ncbi.nlm.nih.gov/pubmed/7974586?tool=bestpractice.com A 70% stenosis calculated according to the NASCET criteria corresponds to an 82% stenosis according to the ECST criteria. The NASCET method routinely provides a lower percent stenosis than the ECST method, a relationship that is best defined by the following equation:

ECST % stenosis = 0.6 (NASCET % stenosis) + 40%.