Atheroembolism

Pathogenesis

Atherosclerotic plaques contain porridge-like material, mainly cholesterol esters, within their center cores. When plaque surfaces become denuded, their contained material, acicular cholesterol crystals and fibrinoplatelet debris, can embolize. A single embolic episode can occur with acute plaque rupture, but the usual course of atheroembolism consists of multiple episodes of embolic showers. Although asymptomatic ulcerated plaques commonly exist in the atherosclerotic aorta and other large vessels, embolization from them begins spontaneously or is triggered by a specific event.

Openly ulcerated plaques are covered by a fibrin layer separating underlying atheromatous debris from the blood stream. With spontaneous atheroembolism or following catheterization and anticoagulation, the fibrin layer becomes unstable, thus promoting showers of microemboli. This microdebris traverses the large and medium-sized vessels, ultimately lodging in small arteries, arterioles, and precapillary arterioles. Atherosclerotic aneurysms also give rise to microemboli consisting of typical cholesterol crystals and atherosclerotic debris. Microemboli have been documented in renal and muscle biopsies, the skin, the urinary tract tissues, bone marrow, lymph nodes, larynx, and virtually the entire gastrointestinal tract. Acicular cholesterol crystals cause an intense inflammatory reaction within the arteriolar wall, resulting in patchy ischemia of affected organs and tissues, scarring, fibrosis, and infarction with tissue loss.

The clinical picture of aeroembolism relates to the arterial location of ulcerative or aneurysmal atheromatous disease. The aorta, sometimes in its entirety (shaggy aorta), is most commonly involved. Less commonly, the iliac and femoral popliteal segments are affected. Mobile polypoid atheromas within the ascending aorta are another distinct source of atheroemboli. In these cases, atheroembolism affecting the brain or upper extremity is a particular problem during cardiac surgery procedures. These lesions are best detected by transesophageal echocardiography (TEE) and other imaging techniques. In contrast to the diffuse form of shaggy descending aortic involvement, atherosclerotic polyps in the ascending aorta appear as discrete lesions.

It is useful to consider clinical manifestations of atheroembolism based upon intensity and distribution of lesions involving the ascending thoracic aorta, the suprarenal thoracoabdominal aorta, the infrarenal abdominal aortoiliac segments, and the femoral arteries. Each require distinct approaches to diagnosis and treatment.