Placa de ateroma da bifurcacao carotidea: como identificar a lesao "activa"?

Summary, in English

The identification of carotid atheromatous plaques associated to a higher neurologic risk may be important in therapeutic decision making for asymptomatic patients and symptomatic patients with 50%-70% stenosis. The introduction of high-definition ultrasonography (HDU) and computer-assisted image analysis provides the possibility of a standard, objective and detailed characterization of the structure of the carotid plaque. The aim of this study is to analyse the relationship between the ultrasonographic characteristics of a group of plaques and the risk of associated cerebrovascular events and cerebral infarction. MATERIAL: One hundred carotid bifurcation plaques (in 68 patients) were studied for the presence of ipsilateral cerebrovascular events. In 61 patients (87 plaques), a correlation with CT scan for the presence of cerebral infarction was possible. METHOD: The lesions were studied by HDU (ATL-HDI 3000) and digitalized for computer-assisted standardization of the image. The analysis included the appreciation of the histogram of the image gray-scale pixel distribution by use of commercial software Adobe Photoshop 3.0. The parameters analysed for global echogenicity were the median of the histogram and the percentage of percentile 40 hypoechogenic pixels (40). Statistical analysis was made with STATA 4.0 software with categorical variables analysed by chi-square and Fisher's exact test and continuous variables analysed by variance analysis and Student's t test. RESULTS: Thirty eight (38%) plaques were symptomatic and 34 (39.1%) were associated to cerebral infarction. The degree of stenosis was > 70% in 51%; between 50 and 69% in 27% and < 50% in 22%. The mean of the median and P40 values was 33.9 and 60.3% in the symptomatic and 46.8 (p = 0.005) and 46.6% (p = 0.001) in the asymptomatic plaques respectively. In the plaques associated to cerebral infarction, it was 32.7 and 61.6% respectively, and in the ones with negative CT scan, it was 44.6 (p = 0.005) and 48.1% (p = 0.002). The mean of the median in the plaques vs. degree of stenosis was: > 70%--33.3; 50-69%--45.1; < 49%--57.7 (p < 0.001). In the series the cut-off point for the median value was 32 and for P40 it was 43 (for any degree of stenosis): G1--plaques < 32 (echolucent); G2--plaques > 32 (echogenic). In G1 symptoms occurred in 60% of the plaques and in 26% of the plaques in G2 (p = 0.0001). CT scan was positive in 66% of the echolucent plaques and in 25% of the echogenic plaques (p = 0.0238). CONCLUSION: 1. The more echolucent plaques are associated with a significantly higher neurological risk. 2. The plaques associated with higher degrees of stenosis are more echolucent. 3. The use of a standard and objective methodology in the analysis of the echographic structure of carotid plaques is important and limits the known intra and inter-observer variability of subjective appreciation.