Purpose: To compare the diagnostic accuracy of colour-Doppler sonography and CT-angiography in the selection of extracranial stenosis of the internal carotid artery to be treated with either endarterectomy or percutaneous transluminal angioplasty.
Materials and methods: A total of 35 atherosclerotic plaques in 20 patients were studied with colour-Doppler sonography and CT-angiography (technical parameters: 2 mm raw thickness; 3.5 helical pitch; 2 mm image thickness; 1 mm reconstruction interval; non ionic contrast medium; Iodine concentration: 400 mg/ml, injection rate 5 ml/sec; Sure Start). On colour-Doppler sonography, we evaluated: the level of geometric stenosis (NASCET classification), maximum systolic peak velocity at the point of maximal stenosis and post-stenotic flow features. On CT-angiography we evaluated the level of geometric stenosis (NASCET classification) and the presence of calcium. We compared the degrees of geometric stenosis obtained with both techniques and considered the role each technique had in selecting candidates for surgery. CT-angiography was considered the gold standard.
Results: Three out of 35 plaques on CT-angiography were determining total carotid occlusion; all three of them were also shown on colour-Doppler sonography; 12 of 35 plaques were responsible for a degree of stenosis over 60% on CT-angiography and 11 of them (91.6%) were correctly shown on colour-Doppler sonography. 19 out of 35 plaques were determining a degree of stenosis less than 60% on CT-angiography and 11 of them (89.5%) were correctly shown on colour-Doppler sonography. The positive and negative predictive values were 92.3% and 95%, respectively, in detecting the plaques responsible for a degree of stenosis greater than 60%.
Discussion and conclusions: Colour-Doppler sonography is considered the first step in the diagnostic work-up of carotid atherosclerosis and evaluation of plaque conspicuity to select which plaques need to be treated with endarterectomy or percutaneous transluminal angioplasty. It has not been clearly demonstrated whether colour-Doppler sonography should be regarded as the sole preoperative imaging test or whether more expensive and invasive procedures such as CT-angiography, MRI and angiography are required. This study suggests that the accuracy of colour-Doppler sonography is comparable to that of CT-angiography in evaluating the degree of geometric stenosis caused by the plaque; in addition, it provides functional information on the plaque's haemodynamics effects. CT-angiography, rightly regarded as the gold standard, should be used for evaluating plaque composition (in particular predicting calcium presence and conspicuity) and in those cases in which the sonographic evaluation is not conclusive.