Invited commentary

Abstract

Determining the degree of carotid artery stenosis (CAS) is critical in the decision to perform carotid artery intervention, and the applicability of the randomized controlled trial results is based on making these determinations via specific methods. Duplex ultrasonography (DU) is an accurate diagnostic tool, however, traditional DU provides only an inferred estimate of CAS based on velocities acquired with spectral analysis. Flow velocity criteria were initially developed based on a correlation of the Doppler-derived values with digital subtraction angiography (DSA). While DSA has customarily been touted as the “gold-standard”, it does have limitations: in particular, only the residual lumen of the vessel is visualized; measurements of the outer wall diameter of the vessel, especially in the area of the carotid bulb, may be subjective. The North American Symptomatic Carotid Endarterectomy Trial (NASCET) method of angiographic measurement was developed partially in order to overcome this subjectivity: the diameter of the distal normal-appearing internal carotid artery, opposed to the carotid bulb, is used as the denominator in the diameter reduction calculation. Computed tomographic angiography (CTA) has the potential to be a valuable tool.1Berg M.K. Zhang Z. Ikonen A. Sipola P. Kalviainen R. Manninen H. et al.Multi-detector row CT angiography in the assessment of carotid artery disease in symptomatic patients: comparison with rotational angiography and digital subtraction angiography.AJNR Am J Neuroradiol. 2005; 26: 1022-1034PubMed Google Scholar CTA offers a unique ability to visualize the plaque itself and the accurate location of the vessel's outer wall. A recent study has reported that while CTA possessed 91% accuracy, the degree of stenosis was underestimated compared with DSA; this was especially true in severely stenotic arteries with a diameter of ≤3 millimeters.2Maldonado T.S. What are current preprocedure imaging requirements for carotid artery stenting and carotid endarterectomy: have magnetic resonance angiography and computed tomographic angiography made a difference?.Sem Vasc Surg. 2007; 20 (2-5-15)Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar The current study is proposing that a more realistic representation of the actual degree of CAS may be supplied by CTA supplemented with high-resolution B mode ultrasound. The authors' suggestion is that CAS may be better defined by comparing the residual lumen of the vessel at the area of maximal stenosis to the true “outer wall” diameter of the vessel at that particular location. This concept is provocative, however, this method is markedly different from the currently accepted NASCET-type calculation, and even subtly different from the European Carotid Surgery Trial (ECST) type measurement, which used as the denominator the estimated diameter of the carotid bulb based on DSA (even if the point of maximal stenosis was not at that particular location). In this interesting report, B-mode imaging measurements with validation by CTA were used in receiver-operator curve (ROC) analysis to determine optimum thresholds for each hemodynamic parameter. However, although the detailed information and measurements derived from CTA or high-resolution B-mode ultrasound may ultimately prove to be more comprehensive than, and perhaps even superior to, current DSA imaging, for the time-being neither can currently be considered a “gold-standard.” Perhaps most importantly, this report illustrates that there are no universally accepted duplex criteria that absolutely signifies any specific degree of CAS. A clinician cannot simply accept a report of CAS from a noninvasive vascular laboratory without knowing which type of duplex criteria and/or angiographic correlation has been used to provide the output.3Rockman C.B. Riles T.S. Lamparello P.J. Giangola G. Adelman M.A. Stone D. et al.Natural history and management of the asymptomatic, moderately stenotic internal carotid artery.J Vasc Surg. 1997; 25: 423-431Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar As increasing numbers of vascular surgeons are performing carotid endarterectomy without arteriography, the accuracy and standardization of the duplex scan and other newer imaging studies used to measure degrees of CAS is a critical theme.