July 22 (HealthDay News) -- One part of the carotid artery that supplies the brain with blood actually expands when deadly plaque builds up, but two other sections don't, and that can lead to a fatal stroke, researchers at Wake Forest University Baptist Medical Center have found.

MRIs revealed that the common segment shared by the right and left carotid arteries expands by 11 percent, on average, to keep blood flowing when complex plaque -- made up of cholesterol, calcium and fibrous tissue -- forms. Meanwhile, the internal carotid artery, which leads to the brain, decreases by as much as 16 percent when people have atherosclerotic plaque in their blood. The artery wall also grows an average of 14 percent thicker, the researchers found.

The findings came from MRIs of 191 men and women who had no symptoms of carotid artery disease.

"This may help explain why so many significant blockages occur in the internal carotid and the (nearby) bulb area and so few occur in the common segment, which seems to be protected," J. Greg Terry, a research associate in the endocrinology section of internal medicine at Wake Forest, said in a news release from the medical center. Terry presented the findings in June at the International Symposium on Atherosclerosis in Boston.

It is not known why segments respond in such different manners, though the researchers theorize that differences in arterial anatomy or local blood flow patterns, possibly caused by individual genetics or other risk factors, could be responsible.

SOURCE: Wake Forest University Baptist Medical Center, news release, July 14, 2009