Fatty streakstext annotation indicator are the first signs of atherosclerosis that are visible without magnification. A fatty streak consists of lipid-containing foam cells in the arterial wall just beneath the endothelium. It appears as a yellow discoloration in the artery's inner surface and occurs in the aorta and coronary arteries of most people by age 20. Over time, these fatty streaks can evolve into atherosclerotic plaques or they can remain stable or even regress. The image below on the left is a photograph of the inside of an artery; one can see a fatty streak beneath the thin endothelial lining of the artery. The cartoon on the right summarizes the steps by which the fatty streak evolves.
The cartoon on the right also emphasizes the role of T-lymphocytes, which are also in the intima. They secrete cytokines that induce smooth muscle cells to migrate from the media to the intima. These smooth muscle cells also begin to proliferate under the influence of growth factors. Over time there is a progressive accumulation of lipid and smooth muscle cells, and eventually the growing lesion begins to raise the endothelium and encroach on the lumen of the artery. This is depicted in the image below, which shows a cross-section of an artery the site of an atherosclerotic plaque.