Abstract:
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Purpose: Carotid Doppler ultrasound (CDU) of a very severe stenosis may have velocities in the normal range (peak systolic velocity (PSV) less than 200 cm/sec) as blood flow precipitously decreases. By velocity criteria alone, these stenoses could be mistaken for a non-significant stenosis. Our study compared the diameter of the internal and external carotid arteries (ICA, ECA) measured on CDU to determine if calculating the average diameter ratio (ADR) of the ICA versus ECA could accurately diagnose very severe stenoses of the ICA with PSV values in the normal range.
Methods and Materials: A single centre retrospective audit of patients having undergone CDU and carotid angiography (CA) within 99 days was performed to obtain data sets consisting of PSV values and percent stenoses, termed carotid units (CU). Beginning in January 2003 to the present, prospective measurements of the diameter of the ICA and ECA have been obtained. Measurements were taken from a transverse image above the carotid bifurcation showing both the ICA and ECA just beyond any plaque or stenosis. ADR = diameter of ICA (T + AP) / diameter of ECA (T + AP); T=transverse, AP = anteroposterior
Results: 72/540 (13%) of CU had a very severe (90% or greater) ICA stenosis. Of these, 6/72 (8%) were found to have a PSV in the normal range (< 200 cm/sec). These cases were identified retrospectively, and measurements of the ICA or ECA were not obtained. Although the ICA appeared small in calibre in each case, 3/6 (50%) were misdiagnosed as a mild stenosis based on the PSV in the normal range (19 - 114 cm/sec). 19/186 (10%) of CU in which measurements of the ICA and ECA were obtained underwent CA. 6/19 (32%) had no stenosis on angiography; the average (range) ICA/ECA ADR was 1.2 (1.1-1.7). 3/19 (16%) had an ADR less than 1. Two of these CU had a very severe ICA stenosis - 95%. The other had a mild (30%) stenosis, however the diameter measurements of the ICA for this CU were incorrectly taken within rather than beyond the ICA stenosis.
Conclusion: An ICA/ECA ADR less than 1, measured correctly, correlates with a very severe ICA stenosis. This may prove useful to objectively differentiate mild from very severe stenoses in which the PSV is in the normal range. We are continuing to gather data on this measurement to more accurately define its statistical performance as a sign of a very severe carotid stenosis.
Nicoletti RDMS, M,
Diagnosing Very Severe Internal Carotid Artery Stenosis by Doppler Ultrasound Using A New Measurement--The Average Diameter Ratio of the Internal to External Carotid Artery: Work in Progress. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3101498.html
