Complicated atheroma. Light micrograph of a section through an artery that is affected by a complicated atheromatous lesion. Atheroma is the deposition of fatty material on the inner walls of an artery. This deposit is known as a plaque (light pink, left side). As the plaque enlarges, the blood supply to the vessel lining may be cut off leading to cell death (necrosis) and causing the surface to become ulcerated. This rough surface causes coagulation of the blood and the formation of a thrombus (dark pink, right side) at the site of the ulcerated atheroma.