Comparison between the NASCET method and subjective visual impression in the evaluation of internal carotid artery stenosis

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Abstract
OBJECTIVE: To evaluate the accuracy of subjective visual impression (SVI) of an experienced neuro-radiologist in the measurement of the degree of internal carotid artery (IC) stenosis evaluated by digital angiography (DGA). METHOD: Ten symptomatic patients with internal carotid stenosis greater than 70% in a previous duplex scan were submitted to DGA. The degree of stenosis in both sides (symptomatic and asymptomatic) were evaluated by the same neuro-radiologist who gave his SVI and applied the NASCET method immediately after. Both methods were compared using the intraclass correlation coeficient (r) and its 95% confidence interval (95% ci). For each method, the sample (20 ICs) was also divided in surgical (stenosis between 70 and 99%) and non surgical ICs, using kappa concordance coeficient (k) to compare the results. RESULTS: The results comparing the 20 values obtained by each method are: r = 0.90 (95% ci: 0.77 -- 0.96). Dividing the sample in surgical and non surgical ICs, k = 0.857, p < 0.0001; sensitivity = 100% (39.6% - 100%); specificity = 93.8% (67.7% - 99.7%); positive predictive value = 80% (29.9% - 98.9%); negative predictive value = 100% (74,7% - 100%). CONCLUSION: The SVI may be used by at least some experienced neuroradiologists as a preliminary tool to evaluate the degree of IC stenosis with DGA, but a standardised and well established method should be routinely performed.

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