Hypoechoic areas on ultrasound images of atheroma are not always diagnostic of fatty plaque.

Atherosclerotic plaques in ultrasound (US) images may have bright areas suggestive of fibrous plaque and hypoechoic areas that are often interpreted as fatty plaque. The current study was designed to test the hypothesis that fibrous tissue in atherosclerotic plaques will be hyperechoic or hypoechoic, depending on collagen fiber morphology. Twelve segments of aortic arch containing atherosclerotic plaques obtained from cadavers were imaged with an 8-MHz US transducer, then sectioned, stained with picrosirius red and examined with polarized light microscopy. There were 12 bright areas that contained predominantly thick collagen fibers. Two areas were anechoic, with predominantly thin collagen fibers. There were 11 hypoechoic areas; six of these contained thin fibers and five contained no collagen on polarized light microscopy, suggesting fat or thrombus. We conclude that fibrous aortic plaques consisting of predominantly thin fibers appear hypoechoic or anechoic on US images and, therefore, may be indistinguishable from fatty plaques.