Table 1 Ultrasonographic classifications of carotid plaques Gray-Weale (1988) and Geroulakos (1993) Johnson (1985) Type 1: predominantly echolucent with a thin echorich cap Type 2: dominantly echolucent lesions with small areas of echogenicity Type 3: dominantly echogenic lesions with small (< 25%) areas of echolucency Type 4: echorich homogeneous Type 5: plaques with acoustic shadowing caused by calcification Soft (low level echoes) Soft (low level echoes) Dense (high level echoes) Dense (high level echoes) Calcified The risk of ischemic events related to carotid plaques is also much associated with their histological morphology. Plaque echogenicity as assessed by B-mode ultrasound has been shown to correlate with histological findings. Echolucent plaques consist of a thin fibrous echogenic cap overlying a lipid core with high macrophage content and, sometimes, zones of hemorrhage. When the cap is thinner than 5–10 µ it may not be detected by ultrasound. Echogenic plaques consist of dense fibrous tissue and their echogenicity increases with increasing amounts of collagen. The presence of calcifications results in high echoes in corresponding areas with acoustic shadowings (Goes et al 1990; ECPS Group 1995). Several classifications have been proposed to group carotid plaques according to their appearance on ultrasound (Table 1). Echolucent and heterogeneous plaques are described as the most vulnerable, rupture-prone lesions and have been associated with neurovascular symptoms and an increased risk of ischemic stroke (Polak et al 1998; Grønholdt, Norderstgaard, et al 2001; Mathiesen, Bønaa, et al 2001; Tegos et al 2001). Echogenic plaques are most frequently associated with asymptomatic status (AbuRahma et al 2002). In a general population, the ratio of subjects with echolucent plaques to subjects with echogenic plaques is approximately 1:2 (Joakimsen et al 1999; Zureik et al 2003). Ecolucent plaques dominate in patients with symptomatic carotid disease, while asymptomatic patients usually have echogenic plaques (Steffen et al 1989). It should be noted, however, that carotid plaques are dynamic structures that change in composition over a period of time. Patients with recent symptoms are more likely to have echolucent plaques compared with patients with earlier symptoms (ECPS 1995). In patients evaluated for chest pain and in those with acute coronary syndromes, there is a stepwise increase in Carotid and coronary artery disease Reilly (1983) Heterogeneous (high, medium, and low level echoes) Heterogeneous (high, medium, and low level echoes) Heterogeneous (high, medium, and low level echoes) Homogeneous (medium or high level echoes) Homogeneous (medium or high level echoes) ECPS (1995) Ecolucent heterogeneous Ecolucent heterogeneous Intermediate Echorich homogeneous Echorich homogeneous the number with carotid disease with the increasing severity of CAD (Kallikazaros et al 1999; Komorovsky et al 2005). A gradual increase in the proportion of echogenic carotid plaques was observed with the increase of the extent of CAD, while the proportion of echolucent carotid plaques remained unchanged (Figure 1) (Komorovsky et al 2005). This could reflect the natural development of more organized and calcified plaques in more advanced stages of atherosclerosis. Recently, Lombardo et al (2004) classified carotid plaques as complex (those with irregular surface and/or heterogeneous echogenicity involving > 50% of the plaque area, including echolucent, mobile, and ulcerated plaques) and simple (plaques with smooth surface and a homo- geneous hyperechoic structure involving > 50% of the plaque area). They demonstrated that complex carotid plaques are more prevalent in patients with unstable angina pectoris 60 )50 % ( e s ie40 a s d d i t ro30 a c h t iw20 s t n e i ta10 P 0 19 % 17 % 10 % 26 % 12 % 31 % 16 % 36 % 0-VD 1-VD 2-VD 3-VD Extent of coronary artery disease Figure 1 Distribution of echolucent and echogenic carotid plaques according to the extent of coronary artery disease in the entire study population. Data adapted from Komorovsky et al (2005). Abbreviations: VD, vessel disease. NOTE: black bars = echogenic carotid plaque group; white bars = echolucent carotid plaque group. Vascular Health and Risk Management 2005:1(2) 133