Are strokes more likely to result from severe carotid atherosclerotic stenoses? If not, why not?

The authors studied by carotid duplex ultrasonography 478 unselected elderly patients (age sixty to one hundred one years, mean 82 +/- 8), in their long-term health care facility. Of these, 108 had previously experienced strokes owing to atherothrombotic brain infarcts, documented by a neurologist, and 370 had not. The degree of extracranial internal or common carotid narrowing in these patients was classified by standard Vmax Doppler criteria as 0-40%, 40-80%, and 80-100% luminal diameter reduction. The authors found that 87% of the patients had little or no carotid stenosis (0-40% luminal diameter reduction). Nevertheless, 79% of the previous strokes had occurred in these patients, and the incidence of strokes in this group was 21%. Severe, but not mild or moderate, degrees of carotid obstruction (80-100% luminal diameter reduction) were associated with a 100% stroke incidence. The authors conclude that strokes most commonly result from causes other than ischemia due to in situ severe extracranial internal or common carotid stenosis or occlusion.