OBJECTIVES: It has been suggested that a juxtaluminal black (hypoechoic) area (JBA) in ultrasonic images of asymptomatic carotid artery plaques is associated with a lipid core close to the lumen or a thrombus on the plaque surface. The aim of our study was to test the hypothesis that the presence and size of JBA predicts future ipsilateral ischemic stroke.
METHODS: JBA was defined as an area of pixels with gray scale value <25 adjacent to the lumen without a visible echogenic cap, after image normalization. The size of a JBA was measured in the carotid plaque images of 1,121 patients with asymptomatic carotid stenosis 50-99% in relation to the bulb (ACSRS study), followed-up for up to 8 years.
RESULTS: JBA had a linear association with future stroke rate. The area under the ROC curve was 0.816. Using Kaplan Meier curves, the mean annual stroke rate was 0.4% in 706 patients with JBA <4 mm2; it was 1.4% in 171 patients with JBA 4-8 mm2, 3.2% in 46 patients with JBA 8-10 mm2 and 5% in 198 patients with JBA >10 mm2 (p<.001). In a Cox model with ipsilateral ischemic events (AF, TIA or stroke) as the dependent variable, JBA (<4, 4-8, >8) was still significant after adjusting for other plaque features known to be associated with increased risk (stenosis, GSM, presence of discrete white areas without acoustic shadowing (DWA) indicating neovascularization, plaque area and history of contralateral TIA or stroke. Plaque area and gray scale median (GSM) were not significant. Using the significant variables (stenosis, DWA, JBA and history of contralateral TIA or stroke), this model predicted the annual risk of stroke (range 0.5-10.0%). The average annual stroke risk was <1% in 734 patients, 1-1.9% in 94, 2-3.9% in 134, 4-5.9% in 125 and 6-10% in 34.
CONCLUSIONS: The size of JBA is linearly related to the risk of stroke and can be used in risk stratification models. These findings need to be confirmed in future prospective studies or in the medical arm of randomized controlled studies in the presence of optimal medical therapy.