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Background and Purpose: Advances in carotid plaque imaging could allow quantification of fibrous cap thickness in vivo. While a cap thickness <65 microm is the accepted definition of rupture-prone plaque in the coronary circulation, the threshold value for carotid plaques is unknown., Methods: We made detailed histological assessments of 526 carotid plaques from consecutive patients undergoing endarterectomy for symptomatic carotid stenosis. The thickness of the fibrous cap at the thinnest and most representative part was measured., Results: Cap thickness could be measured reliably in 428 (81%) plaques. In the ruptured plaques (n=257), the median representative cap thickness was 300 microm (IQR 200 to 500 microm) and the median minimum cap thickness was 150 microm (80 to 210 microm; mean=181 microm), which is much greater than the mean cap thickness of 23 microm at the point of rupture that has been reported for coronary plaques. For nonruptured plaques, the median cap thickness values were 500 microm (300 to 700 microm) and 250 microm (180 to 400 microm), respectively. The optimum cut-offs for discriminating between ruptured and nonruptured plaques were a minimum cap thickness <200 microm (OR 5.00, 3.26 to 7.65, P<0.001), a representative cap thickness <500 microm (OR 3.38, 2.25 to 5.08, P<0.001), or a combination of both (OR 5.11, 3.19 to 8.19, P<0.001). Minimum and representative cap thickness were only modestly correlated (r(2)=0.30) and were both independently associated with cap rupture., Conclusions: Critical cap thickness is greater in carotid plaques than coronary plaques. Minimum and representative cap thicknesses were both independently associated with cap rupture. A combination of minimum cap thickness <200 microm and a representative cap thickness <500 microm identified ruptured plaques most reliably. Prospective imaging studies are required to establish whether these cut points predict clinical events in patients with asymptomatic carotid stenosis.

Purpose of Review: Patients with asymptomatic carotid stenosis are at increased vascular risk but optimal treatment is controversial. We reviewed the current evidence for medical and surgical intervention in these patients., Recent Findings: Optimal medical treatment is the most important aspect of management of patients with asymptomatic carotid stenosis. On the basis of previous trials, endarterectomy is only of overall benefit in men, and this benefit may now be obviated by improved medical treatment. There is insufficient evidence to advocate the routine use of carotid angioplasty or stenting in patients with asymptomatic stenosis. Inaccuracy in the measurement of carotid stenosis may contribute to conflicting estimates of stroke risk in relation to the degree of asymptomatic stenosis. Advances in noninvasive imaging of plaque morphology and inflammation and the detection of microembolic signals may help to risk stratify patients but data on clinical usefulness are lacking., Summary: Absolute benefit from endarterectomy for asymptomatic carotid stenosis is small, but can sometimes be justified in men. Further research is required to determine long-term benefit in women and to risk stratify patients, particularly in the light of advances in medical treatment.

Background and Purpose: Carotid plaque instability is an important determinant of stroke risk. There are now a number of different imaging techniques that provide information on carotid plaque morphology. However, it is unclear how they compare with one another or whether they can reliably assess plaque instability. Studies comparing imaging with pathology have shown highly variable results, even for similar imaging techniques. This may be because of variable pathology techniques rather than differences in imaging., Methods: We performed a systematic review of studies that compared carotid imaging with histology of the excised plaque published between January 1995 and September 2004. We assessed the quality and comparability of these studies. In particular, we determined which histology methods were used and whether observer reproducibility of the histology assessment was reported., Results: Among 73 eligible studies, histological methods were poorly reported and highly variable; 23% reported reproducibility data for imaging and only 12% reported reproducibility data for histology. Of 29 studies that reported quantitative results of blinded comparisons, there were methodological deficiencies and the results were highly variable. No study considered the extent to which the lack of reproducibility influenced the imaging-pathological correlations reported., Conclusions: Pathological correlation in studies of carotid plaque imaging cannot be reliably interpreted or compared because of incomparable and poorly reported histology methods. We make recommendations for the performance, reporting, and interpretation of imaging-pathological correlation studies and highlight the need for consensus guidelines.